Dominant male of Apistogramma sp. “Mitu” approaching a subdominant conspecific.
(Photo: Frank Hättich)

      Apistogramma sp. “Mitu” was discovered in the year 1992 by the German Uwe Werner (Ense-Bremen) and his fellow travellers in the Río Vaupés drainage north of Mitú, the capital of the Colombian province Vaupés, and introduced for the first time in GLASER & GLASER (1996) under the name Apistogramma sp. “Río Vaupes”.
In order to avoid confusion with Apistogramma uaupesi KULLANDER, 1980, RÖMER (1998) proposed Apistogramma sp. “Mitu” as the new common name still commonly used for this species until today.

Apistogramma sp. "Mitu", female collected in 1992, in beginning territorial coloration. (Photo: Uwe Werner)

Apistogramma sp. "Mitu", adult male collected in 1992.
(Photo: Uwe Werner)

     Unfortunately, Werner didn’t succeed in breeding the few animals brought back from Colombia, so that the species had quickly disappeared from the aquarium hobby shortly after its discovery and first import. During the last years, fish probably representing Apistogramma sp. “Mitu” appeared sporadically as by-catches in Asia, however, to our knowledge no live specimens arrived in Europe since 1992.

     Then, in 2015, one of the authors (DM) discovered a small and slender Apistogramma species unknown to him at that time among Apistogramma cf. personata offered by a local fisherman. This species has subsequently been included in the nominal reference system introduced by DM and TC under the name Apistogramma sp. “D6” (cf. HÄTTICH & KIPPER 2017).

     Via the Canadian company Below Water, these animals have then been exported to Asia under the trade name Apistogramma sp. “Slender Gold” ¹ Endnote 1 ¹ The choice of the trade name “Slender Gold”, instead of the less impressive designation “D6”, was probably made primarily due to the hoped-sales-promoting effect. However, it is not a pure fantasy name as it refers to two characteristics of the species. In both sexes of this slender species often a golden shimmering shine appears on the body, produced by the interplay of shining scales and the (also in males) frequently yellowish basic coloration of the body.

       Photos: Daniel Mejia – apparently, however, without finding greater distribution there.

Seven months old, colourful male of Apistogramma sp. “Mitu”. (Photo: Tom Christoffersen)

     It took another two years until animals of this species were caught again by chance.
During his search for Corydoras sp. “CW104” one of us (DM) accidentially got numerous Apistogramma sp. “D6” into his net. As it turned out later, they were collected at the same location they already had been caught as by-catches of Apistogramma cf. personata in 2015.

     In spring and December 2018 further specimens were collected there, some of which also reached Europe.
A comparison with the photograpic material of the fish collected in 1992 provided by Werner and preserved specimens of the “Mitu”-Apistogramma from the personal collection of UR did not reveal any relevant differences to Apistogramma sp. “Mitu”. Moreover, since Apistogramma sp. “D6” originates from the same Río Vaupés tributary as Apistogramma sp. “Mitu", there is no reasonable doubt for us to accept that they actually are the long known “Mitu”-Apistogramma.

Habitat

     In April 1992 Werner and fellow travellers caught some specimens of Apistogramma sp. “Mitu” in the vicinity of rapids in the Río Cuduyari, a left side tributary that flows into the Río Vaupés north of Mitú. The Río Cuduyari is a blackwater river that originates in the Colombian Guiana highlands. However, its water has a less intensely brown colour compared to other blackwater rivers in the region. This could be due to the fact that some of its tributaries – typical for the Río Vaupés ² Endnote 2 ² Colombian spelling. drainage – carry clear water.

     At the place of discovery the water had a temperature of 29.5 °C, pH of 4.8, carbonate hardness of 4.5°KH, and no detectable total hardness (WERNER pers. comm. to FH).
In addition to Apistogramma sp. “Mitu”, with Apistogramma cf. personata (A172) another Apistogramma form (back then also new to the hobby ³ Endnote 3 ³ In the meantime identified to represent Apistogramma personata KULLANDER, 1980 (cf. RÖMER et al. 2017a)! ) was captured here. In the meantime it has however also been found at numerous other sites in the vicinity of Mitú.

Sandy beach in the Río Cuduyari: In spite of a recognizably low structuring, sometimes large numbers of Apistogramma sp. “Mitu” were collected in habitats like this one.
(Photo: Tom Christoffersen)

Collecting Apistogramma sp. “Mitu” on a sandy beach in the Río Cuduyari
(December 2018). (Photo: Tom Christoffersen)

Apistogramma sp. “Mitu” just collected in the Río Cuduyari (December 2018).
(Photo: Tom Christoffersen)

     The “Mitu”-Apistogramma collected by DM in 2017 and 2018, as well as the specimens exported to Asia as Apistogramma sp. “Slender Gold” in 2015, were also collected near to rapids of the Río Cuduyari. Reflecting all facts, it seems to be probable, that these are the same ones where Werner collected his specimens a quarter of a century earlier.

     Apistogramma sp. “Mitu” were collected there during the dry season in an area of about one kilometre of length on three sandy beaches. Here the depth of the water of the Río Cuduyari was more than two metres and the teabrown water had a pH value of 5.2. The Apistogramma were mainly caught at a depth of less than one metre, in areas where there was less current than in the deeper areas. In some cases, more than a hundred individuals of this species were caught at once in a ten-metre-wide seine net. However, in the shallower areas with about 30 cm and less depth and very slow current, only a few specimens were caught.

     These sandy beaches themselves offer no hiding places for the Apistogramma. This could be the reason why neither territorial, nor courtshipping or breeding animals were observed. Possibly, reproduction is primarily limited to the rainy season when the flooded shore-forests with its numerous hiding places are available to the fish.

     Observations by RÖMER (1994), which were later confirmed by other observers (quoted in RÖMER 1998), indicate the possibility that larger groups, sometimes even very large aggregations of thousands of Apistogramma, some of them actually migrant, might, off their reproduction period, regularly reside in and arround areas of such sandbanks.
According to his research, these groups often consist of several different species of the genus. In fact, DM also collected two other Apistogramma species together with Apistogramma sp. “Mitu”, Apistogramma cf. personata and Apistogramma sp. “Rautenband/Diamond-band”. While the first of the two latter species seems to be quite widespread in the vicinity of Mitú, the “Rautenband/Diamond-band”-Apistogramma had previously only been found south of the city in a right sided tributary of the Río Vaupés (cf. HÄTTICH & RÖMER 2018).

     In addition to the three Apistogramma species, Corydoras sp. “CW104” as well as species of the genera Cichla BLOCH & SCHNEIDER, 1801, Geophagus HECKEL, 1840, Characidium REINHARDT, 1867 and some large Characidae LATREILLE, 1825 were netted.
It should also be mentioned that, according to local fishermen, Apistogramma sp. “Mitu” supposedly had also been found in the Río Vaupés itself at the peak of the dry season.

Phenotype

     Apistogramma sp. “Mitu” possess a slender and stretched, laterally highly oval only little compressed body shape and hardly reach a total-length of 7 cm in male and 5 cm in female sex. The (also in males) frequently yellowish basic-colour of the body in interaction with shiny scales often leads to a metallic golden shimmering shine on the body of both sexes.

Adult male of Apistogramma sp. “Mitu” in neutral mood.
(Photo: Frank Hättich)

Apistogramma sp. “Mitu”, dominant male, “yawning”, note the slightly upturned mouth typical of Apistogramma, an adaptation to the pecking of particles from the substrate. (Photo: Uwe Römer)

     In particular the males usually show intense red spots or worm-like lines on the lower half of the head in addition to bluish-greenish shimmering glossy markings. In some males, some of these spots even reach far onto the abdomen. The about pupillar-wide suborbital stripe runs without interruption, and usually in a straight line, from the lower edge of the eye, diagonally downward to the lower posterior edge of the gill cover.
The narrow zigzag or zipper-like⁴ Endnote 4 ⁴ This consists of two parallel rows of vertical dashes offset to one another horizontally. lateral band adjoins the postorbital stripe without interception. Depending on mood, it may be continuous or dissolved into segments or side spots.

     It is particularly remarkable that besides Apistogramma borellii (REGAN, 1906), Apistogramma sp. “Mitu”, is the only

Apistogramma sp. “Mitu”, male, with eight vertical bars. The provisional numbering of the vertical bars is inserted. (Photo: Uwe Römer)

species of the genus so far introduced in the literature, that regularly shows eight (!) instead of seven (the normal condition) or six (so far only in one Peruvian form) vertical bars on the body. However, these are seldomly so clearly pronounced that corresponding observations are possible, e.g. on photos taken from them. We too, have therefore only consciously registered this conspicuity after several weeks of maintance!
The different number of bars represents a unique diagnostic feature (an autapomorphy) of this species and at least one other closely related form (see next but one section).
In contrast to species like Apistogramma steindachneri (REGAN, 1908), Apistogramma staecki (KOSLOWSKI, 1985) or some forms related to Apistogramma eunotus, (KULLANDER, 1981), which regularly show more or less clearly split vertical bars 5 to 7 on the caudal peduncle and the posterior half of the body, according to our actual investigations, these are indeed continuous bands which cannot be interpreted as any kinds of derivatives of split bars. Instead, to us, one of the bars 5 or 6 seems to be inserted additionally into the pattern.

Apistogramma sp. “Mitu”, female after being chased away by a conspecific. The eight vertical bars, which are unusual for the genus, are clearly visible. (Photo: Frank Hättich)

Apistogramma sp. “Mitu”, male, typical dominance colouration after egg deposition. Note the characteristic of the side spots and vertical bars. (Photo: Uwe Römer)

     Usually the vertical bars on the body of Apistogramma are numbered starting from the cephalic end. This gives rise to a somewhat curious problem in the present case. The supraorbital stripe and the first four vertical bars are about the same width, the following four too, but only about half as wide as the anterior ones.

Female of the “Mitu” Apistogramma at the beginning of spawning maturity.
(Photo: Frank Hättich)

     The last, i. e. eighth, band is in the same position as the seventh band of other species. This could lead to misunderstandings when comparing the individual bars with those of other species, which is why we present here a visualized proposal for their numbering in the “Mitu”- Apistogramma (see figure attached). In the description of the genus Mazarunia KULLANDER (1990) had proposed a comprehensibly justified count from tail to head. How numbering of vertical bars of Apistogramma should be handled in the future will have to be reserved for detailed scientific investigations. However, due to the large number of species within the genus, a change in the counting method might cause far more problems than the retention of the previous counting system.

     Both sexes of the “Mitu”-Apistogramma may show a distinct lateral spot at the intersection of the lateral band with the third vertical bar. In dominant aggressive individuals, a second lateral spot often appears additionally at the intersection of the lateral band with the fourth bar.

Apistogramma sp. “Mitu”, Portrait of a male, notice body cross-section and blue line patterns of dominant individuals. (Photo: Uwe Römer)

     Between the position of the last and penultimate bar, the lateral band often narrows or possesses a distinct gap. Some females also show such a gap between the edges of the vertical bars 2 and 3. Moreover, the lateral band sometimes widens in the area of the last vertical bar due to the addition of dark scale edges, which can sometimes result in a pattern of diamonds or hexagons on the caudal peduncle quite similar to that of the “Rautenband/Diamond-band”-Apistogramma (HÄTTICH & RÖMER 2018). Moreover, a dark pigmentation sometimes occurs in this area in and around the lateral band (cf. KOSLOWSKI 2002), which is mainly formed by melanophores (black pigment cells) positioned on the crossing points of the scales. If the resulting spot is particularly intense, the impression of a “second caudal spot” may occur (as in Apistogramma sp. “Rautenband/Diamond-band”).

     Both sexes of the “Mitu”-Apistogramma usually show an upper but never a lower pectoral spot as well as – except for a not always visible short (dark)grey to blackish horizontal stripe directly below the lower lip – any black markings on chin, throat and chest.
A mid-ventral stripe was observed so far only in a single female. However, up till now it could not be conclusively clarified whether this animal is not representing an individual of the closely related form Apistogramma sp. “D53”.⁵  Endnote 5 ⁵ We hope that the examination of the genetic material of the offspring of the female in question will clarify this. Some preserved juvenile fish were kindly given to us for this purpose by Erik Bakker.
.

     The low dorsal fin of the “Mitu”-Apistogramma (reaching only approximately half the high of the body) is truncated on its whole length, in males the rear soft-part-is pointed or slightly extended, in females however rounded or (less frequently) slightly pointed, but not extended. Especially when threatening or displaying it carries a blackened seam at its upper edge, which occupies about a quarter of the height of the fin. In addition it is usually delimited by a thin white or bluish/greenish-iridescent band from the downwardly adjacent middle part of the dorsal, which is predominantly pale violet in males and mostly orange in females.

Apistogramma sp. “Mitu”, female in threat display.
(Photo: Frank Hättich)

Male of Apistogramma sp. “Mitu” in lateral threat display.
(Photo: Frank Hättich)

Apistogramma sp. “Mitu”, highly aggressive female defending her brooding territory. (Photo: Frank Hättich)

Apistogramma sp. "Mitu", threatening male in lateral position. (Photo: Frank Hättich)

     The anal fin is also pointed in males and usually sligtly extended, whereas in females it is rounded and (only exceptionally) slightly pointed.
The transparent caudal fin is rounded and shows some vertically arranged whitish-bluish translucent dots or, exceptionally, also vertical stripes, in its central part.
The ventral fins can be extended in both sexes. However, in females they practically don't reach the hardray part of the anal fin, whereas they may regularly reach up to the basis of the second hardray of the anal fin or even clearly beyond in adult males.

Systematic Position

     An assignment of the “Mitu”-Apistogramma to a particular group of related species within the genus can currently only be done on the basis of its phenotypic features and thus, has to stay only provisionally since no genetic data are yet available which would make possible a more secure clustering to a certain species-group.

     Recent work on the genetics of the genus (BRITZKE 2015; TOUGARD et al. 2017; ESTIVALS et al. in print) shows that the molecular biological clarification of kinship relationships within the genus is possible, useful and necessary.

     The zigzag or zipper-like lateral band, the pronounced dorsal spots, the throughout low and truncated dorsal with a clearly set-off seam at its upper margin, and the rounded caudal fin designate Apistogramma sp. “Mitu” as possible representative of the Apistogramma-alacrina-group within the Apistogramma-regani-lineage
(see WISE in prep.)⁶ Endnote 6
⁶ The fact that Apistogramma sp. “Mitu” can show a distinct lateral spot is remarkable, since the absence of it is considered to be a central differentiation criterion of the Apistogramma-regani-lineage from the three other lineages of the genus (KOSLOWSKI 2002, WISE in prep.). However, a concise lateral spot can also be observed regularly in breeding females of Apistogramma cf. alacrina (Guayas) (A108/D18), which also belongs to the Apistogramma-alacrina-group. As with numerous other criteria formulated for the systematization of the genus Apistogramma, it therefore appears that in this case too, it apparently is not an exceptional regularity.

.

     In the Apistogramma-alacrina-group, the species, together with three other forms (see next section), constitutes the Apistogramma-sp.-“Mitu”-complex named after it (WISE in prep.).
Its representatives differ from other species of the Apistogramma-alacrina-group – forming the Apistogramma-alacrina -complex – by smaller body size, more slender, elongated body shape, a slightly larger tail fin in relation to body height, less elongated soft-part of the dorsal and anal fin, a constriction or gap in the lateral band frequently occurring between the last two vertical bars, lack of a lower pectoral spot ⁷ Endnote 7⁷ An exception within the Apistogramma-alacrina-complex in this regard is Apistogramma sp. "Kiemenfleck/Gill-spot" (D37), which does not possess a lower pectoral spot (cf. HÄTTICH & OHNOTA 2018).
, and less pronounced sexual dimorphism.

Apistogramma sp. “Mitu”, female, colouration during defence of about 4 days old larvae against subdominant conspecifics. (Photo: Uwe Römer)

     The deviating body proportions compared to the species of the Apistogramma-alacrina-complex might be the result of a complex eco-morphological adaptation to habitats with comparatively stronger water currents (cf. ARBOUR 2015; ARBOUR & López-Fernández 2014; Astudillo-Clavijo 2015; LÓPEZ-FERNÁNDEZ et al. 2014).

     Besides the “Mitu”-Apistogramma, the Apistogramma-sp.-“Mitu”-complex also includes Apistogramma cf. sp. “Mitu” (Redbelly), which was imported to Japan in 2015 in only a few specimens, Apistogramma sp. “D53” discovered by DM and TC in a tributary of the Río Vaupés south of Mitú in December 2018, and Apistogramma sp. “D55”, which was collected by them in the same month in the Río Inirida drainage. Unfortunately, only a very small number of these three forms are or have been present in aquaristics so far, so that all statements made in the following about their appearance and differences to Apistogramma sp. “Mitu” have to be regarded as merely provisional.

Differentiation of the forms within the Apistogramma-sp.-“Mitu”-complex

     Like Apistogramma sp. “Mitu”, the form called Apistogramma cf. sp. “Mitu” (Redbelly) probably also originates from the Mitú-area, but its exact location has not yet been clarified. Unfortunately, breeding of the three animals imported to Japan (two males and one female) did not succeed, so that this morph already disappeared from aquaristics. Unfortunately, whether Apistogramma. cf. sp. “Mitu” (Redbelly), like Apistogramma sp. “Mitu”, can show eight vertical bars, is not revealed by the sparse picture material available until now.

Apistogramma cf. sp. “Mitu” (Redbelly), male.
(Photo: Akihiro Shimizu)

Apistogramma cf. sp. “Mitu” (Redbelly), female.
(Photo: Akihiro Shimizu)

But, however, based on this material, they seem to be overall phenotypically identical with the “Mitu”-Apistogramma – except for an extended intensly red blotch on the belly of the males and the absence of red markings on the head. Therefore it might possibly represent a local morph of Apistogramma sp. “Mitu”. On the other hand, works by READY et al. (2006), BRITZKE (2015) and ESTIVALS et al. (submitted) impressively show that geographically isolated forms of a morphospecies may already be separate species, even if differences in their colouration are hardly visible. Since unfortunately none of the three specimens of Apistogramma cf. sp. “Mitu” (Redbelly) has been preserved and no DNA samples were taken (SHIMIZU pers. comm. to FH), we can only hope that this beautiful Apistogramma form will soon be rediscovered in order to obtain more detailed information about its phenotype and its kinship relations.

     Apistogramma sp. “D53” do not differ in their colouration from Apistogramma sp. “Mitu” and like the latter they can also show eight vertical bars, but there are differences in the expression of some other black markings. Their suborbital stripe is often wider and in males it more frequently and more distinctly shows a "V"-shape at its lower end compared to males of the “Mitu”-Apistogramma. In addition, all three brooding females of Apistogramma sp. “D53” observed so far showed a mostly continuous lateral band, a clearly pronounced mid-ventral stripe in the area around the anus, as well as large spots around the ventral fin insertions, which may even form an expanded chest blotch.

Apistogramma sp. “D53”, male. (Photo: Yukitoshi Ohnota)

Apistogramma sp. “D53”, brooding female.
(Photo: Satoshi Tanaka)

In contrast, the lateral band of breeding females of the “Mitu”-Apistogramma is usually dissolved into several side spots or segments, a mid-ventral stripe, if present at all, occurs in exceptional cases only⁸  Endnote 8⁸ As already mentioned, it has not been clarified yet whether the only Apistogramma sp. “Mitu” female so far showing a mid-ventral stripe does not actually represent Apistogramma sp. “D53”.
, if spots at the ventral fin insertions are present, these remain clearly smaller, and a chest blotch has not yet been observed at all. If these differences prove to be relevant, Apistogramma sp. “D53” should be a distinct species. Since in this case, in contrast to Apistogramma cf. sp. “Mitu” (Redbelly), conserved specimens do exist in addition, comparative genetic studies based on that material can be carried out to clarify their species status.

     Apistogramma sp. “D55” differ from the other forms of the Apistogramma-sp.-“Mitu”-complex by the following characteristics: A suborbital stripe that often ends halfway to the lower edge of the gill cover and, if it extends further, may have a distinct gap at this position. In addition, Apistogramma sp. “D55” possess a concise gill cover spot, as it is known in a similar form from the “Kiemenfleck/Gill-spot”-Apistogramma (D37) (cf. HÄTTICH & OHNOTA 2018). Together with the suborbital stripe it may form a very large “V”, that starts at the lower edge of the eye, reaches down to the lower edge of the gill cover and then up until close to the postorbital stripe.

Apistogramma sp. “D55”, male. (Photo: Tom Christoffersen)

Apistogramma sp. “D55”, female. (Photo: Tom Christoffersen)

In contrast to Apistogramma sp. “Mitu” and Apistogramma sp. “D53”, so far no eighth vertical bar has been observed in Apistogramma sp. “D55”. However, they can show a short stripe starting in the area of the upper pectoral fin base, running diagonally back- and downwards, thereby remotly reminding of the third namegiving stripe known from Apistogramma trifasciata (EIGENMANN & KENNEDY, 1903). In addition, the caudal fin of males may show a pattern of vertical stripes which is more regular and consisting of a larger number of stripes compared to males of the other forms. Due to all mentioned differences it is to be assumed that Apistogramma sp. “D55”, native to the Río Inirida drainage, is a distinct species.

Sexual Dimorphism

     As mentioned above, Apistogramma sp. “Mitu” does not show any particularly pronounced sexual dimorphism. Females, which, by means of their colouration do not show up as ripe to spawn or as brooding, are often hard to distinguish from males. They remain smaller and often only appear somewhat less slender and elongated.

Adult female of Apistogramma sp. “Mitu” in neutral mood.
(Photo: Frank Hättich)

Apistogramma sp. “Mitu”, female, colouration in the phase of occupying a cave. (Photo: Uwe Römer)

Apistogramma sp. “Mitu”, male, typical colouration during oviposition. Note the characteristic of the vertical bars.
(Photo: Uwe Römer)

Apistogramma sp. “Mitu”, dominant male, typical neutral colouration in the first days after spawning. Note the absence of vertical bars. (Photo: Uwe Römer)

In females the membranes of the dorsal fin are usually more strongly chamfered or rounded at the top of their backsides than in equally sized males (especially in the anteríor part of the fin). In large males, these can be pointed backwards in the entire hardray part by means of which the upper edge of the fully spread dorsal shows a straight upper edge.

Half portrait of a dominant male of Apistogramma sp. "Mitu". (Photo: Uwe Römer)

     The softpart areas of dorsal and anal fin are rounded in females, exceptionally (in very big specimens) are also slightly pointed, while they are usually pointed or slightly extended in males. In the posterior part at the base of the dorsal, they usually have fewer and less pronounced whitish-bluish translucent spots or stripes than those of males. Moreover, in the central part of the caudal corresponding dots or vertical stripes can be seen more often in males. In addition, females usually have fewer and less pronounced shiny spots and red markings in the head area than their male congeners. However, on their bodies and lips as well as in the area of the caudal spot, they can show the same metallic shimmering splendor as the males. In addition, when viewed from below in a cuvette, the colouration of the throat region between the rear end of the gill cover and the base of the pectoral fins can be used to identify mature females: Here they show a (porcelain)white basic-colouration, whereas that of males and sexually non-mature individuals of both sexes is beige to light-gray, sometimes also pale pink.

Maintenance and Reproduction in Captivity

     Since Apistogramma sp. “Mitu” has so far only been found in blackwater habitats, the water should be soft and acidic and enriched with humic substances to ensure appropriate maintenance conditions. This may be done, for example, by peat filtering, the addition of alder cones or other suitable leaves such as indian almond leaves or leaves of native tree species such as beech and oak. As with all Apistogramma species, very fine, non sharp-edged sand is recommended as substrate enabeling the fish to sift it through for food.

     Like most other members of the Apistogramma-alacrina-group, Apistogramma sp. “Mitu” is not particularly aggressive towards conspecifics. This is a striking difference to the particularly pronounced intraspecific aggressiveness of Apistogramma cf. personata and Apistogramma sp. “Rautenband/Diamond-band” occurring syntopic with Apistogramma sp. “Mitu” in the Río Cuduyari, as well as of Apistogramma sp. "Alto Vaupes II" (D50) also originating from the Río Vaupés drainage (HÄTTICH & RÖMER 2018; RÖMER et al. 2017; RÖMER 2018). Whether the high aggressiveness of these species is based on a common cause is currently still unkonwn (cf. RÖMER 2018).

Apistogramma sp. “Mitu”, dominant male, colouration during inspection of the brooding cave and expulsion of a sneaker. (Photo: Uwe Römer)

Apistogramma sp. “Mitu”, pair shortly before oviposition.
(Photo: Frank Hättich)

Apistogramma sp. “Mitu”, subdominant sneaker in feminine “camouflage” in front of the brooding cave. See text for details. (Photo: Uwe Römer)

Apistogramma sp. “Mitu”, female, colouration in advanced spawning stage.
(Photo: Uwe Römer)

Apistogramma sp. “Mitu”, dominant male, colouration during spawning when approaching spawning site again after leaving it for its defence. (Photo: Uwe Römer)

Apistogramma sp. “Mitu”, female defending the just deposited eggs against subdominant conspecifics. (Photo: Uwe Römer)

Apistogramma sp. “Mitu”, dominant male, aggressive colouration in the phase shortly before the free-swimming of the fry. (Photo: Uwe Römer)

Female of the “Mitu” Apistogramma which showed an exceptionally intense red colouration in her dorsal and caudal fin in the time between spawning and about ten days after the first free-swimming of the fry.
(Photo: Tom Christoffersen)

Dominant female of Apistogramma sp. "Mitu" guarding
few days old fry. (Photo: Uwe Römer)

Apistogramma sp. “Mitu”, male with altered colouration after free-swimming of the fry. See text for details. (Photo: Frank Hättich)

     Breeding of Apistogramma sp. "Mitu" in soft water rich in humic substances (electrical conductivity up to about 100 µS/cm) does not cause any problems. Under these conditions, the pH value appears to be of comparatively minor importance, since breeding was likewise successful at values in the range from 4.5 to 6.5.
The incipient spawning maturity of females is indicated by an increasing corpulence, more intensive yellow colouring, especially of the lower half of the body, black seams at the frontal edges of anal and ventral fins, a black suborbital stripe, black anterior membranes of the dorsal, as well as by the fact that the lateral band is replaced by one or more side spots. If only one side spot is shown, this is the lateral spot.

     The courtship up to the time of spwaning could meanwhile be observed several times. Allready some days ahead of the oviposition a potential place for spawning is selected by the female and from now on its surroundings are defended against other aquarium-inhabitants with continuously rising intensity. Only males of the own species are tolerated in its vicinity. After one of the males has asserted itself during the mating phase which is lasting one to two days, all the other males are forcefully chased from the spawning territory too. In the proper phase of courtshipping preceding the spawning, both partners stay in the territory chosen by the female and inspect potential spawning sites together.
After some time, they preferably stay in immediate proximity of a certain cave (in some cases a different one than originally chosen by the female) and leave this area only in order to feed or to drive away conspecifics. The latter being primarily the task of the male as in most species of the genus. This phase can last from two days to only a few hours in the case of already well-practised partners.

     The forthcoming act of spawning announces itself by the female’s inspection and cleaning of the spawning site taking place in ever more and shorter intervals. At the beginning of this phase, the female's genital papilla is not yet visible, but clearly emerges two to four hours later – about three to five hours before egg deposition starts. During the whole period of observation, the males also stood inside the cave for a short time, either alone or together with the females. However, these stays never lasted longer than half a minute, often only a few seconds. Only few ritualized behavioural elements, as belonging to the courtship-repertory of many Apistogramma species, were observed some times. These consisted of lateral presentation by the male with spread fins and occasional slapping of the caudal fin into the direction of the female and, on the part of the female, presentation of her belly with curved body. With the exception of one male kept by TC, that showed the head-jerking common in courtshipping Apistogramma, no other behaviours typical for the mating of Apistogramma species, e.g. lead- or circular-swimming, have been observed so far, not even immediately before oviposition.

     The nine spawnings observed so far lasted between about 40 minutes and almost two hours. They are initiated by both partners entering the cave. But this time, however, some sand from the inside is piled up in the entrance – usually by the female. During the depositing of the eggs the spawning cave is left again and again for short inspections of its surroundings. It seems interesting that the male usually stays in the cave during the whole time of spawning too. This is actually uncommon in the genus, because the males of almost all species aggressively defend the surroundings of the brooding cave against other fish, while the female attaches the eggs at the spawning site. In this phase, however, they regularly appear at the cave to release their sexual products in or in front of it.
The males of the “Mitu”-Apistogramma are different. They leave the brooding cave only from time to time to drive away other Apistogramma from the surroundings of the cave entrance with short biting attacks, but return to the cave after a few seconds. Though the spawning females occasionally appeared at the entrance of the cave – obviously observing the surroundings – they left it only occasionally for few seconds to drive other fish away.

     Some of UR's observations may provide an indication of possible causes for these seemingly unusual behaviours. During several ovipositions in an aquarium in which a group of “Mitu”-Apistogramma were kept together with Apistogramma personata, it has been observed that small groups of other Apistogramma again and again gathered around the spawning site. Photos and video recordings revealed that these were mainly groups of smaller (subdominant) males of Apistogramma sp. “Mitu” and smaller females of Apistogramma personata. The evaluation also showed that the attacks of the Apistogramma sp. “Mitu” males belonging to the spawning couple were directed primarily towards the smaller males, while the female Apistogramma personata remained virtually unaffected by them. They were, however, the preferred target of the spawning females' attacks. In one case, one of the Apistogramma personata females had been observed swimming into the brooding cave at lightning speed attempting to steal eggs (in vain). It was immediately pushed away from the eggs by severe tail-slapping and biting and seized the escape. This observation suggests that the fish may have gathered in front of the breeding cave to steal the clutch at this early stage. In this phase, in which the couple has several tasks to perform simultaneously – laying of eggs and the defence of the spawning site – there may be more gaps in their defence that could be used for attacks on the clutch by intruders.
The fact that Apistogramma regularly plunder the clutches of other species as well as hunting their small offspring is not only known from aquaristics (RÖMER, 1998, 2006), but also well documented by analyses of the stomach contents from the field (e.g. GOULDING et al. 1988, KNÖPPEL 1970). Besides invertebrates and detritus, larvae and small juveniles of dwarf cichlids were regularly found in the stomachs examined.

     It is noteworthy that the defence strategies of males and females of spawning pairs differ significantly in that they seem to focus on different potential invaders. The obvious question is, why this is the case. In fact, different behavioural strategies in reproduction already observed in Apistogramma may also become discernible here. Female Apistogramma (and other female dwarf cichlids) may be able to optimise their reproductive success by spawning with different males. They thus extend the variety of possible combinations that can be achieved during the fertilization of the eggs by the genetic information units (alleles) originating from different males. The variety of the combinations and the associated chances on optimally adapted descendants is thereby considerably increased. Females of Apistogramma (and almost all sexually reproducing organisms) must therefore have a considerable interest in mating with as many males as possible.
At the same time, however, they should also ensure that the strongest male possible contributes to the rearing of the offspring. In the case of Apistogramma, this contribution is the defence of the larger territory encompassing the female’s breeding territory. For males with an own territory, however, the possible “cheating” behaviour of females implicates considerable disadvantages for them: They have to expect to defend the offspring of other males and thus competitors of their own gene-carriers. They should therefore develop strategies to minimize or even prevent the emergence of such “milkman’s children” in the broods. In the case of Apistogramma sp. “Mitu” this could be clearly seen by the vehement expulsion of all subdominant males of the species from the vicinity of the breeding site.

      However, in many species subdominant males have developed their own strategies to circumvent the aggression of dominant males. One of the best known ones is probably taking on female markings and colour pattern during the approach of the spawning site. This approach usually takes place while the dominant male is busy with territorial defence-tasks. In many cases, the behavior of females ready for spawning is pointedly imitated in addition as soon as the owner of the territory approaches. If the male disguised as a female appears near the entrance to the cave, it is immediately attacked by the spawning female. In fractions of a second, the male “camouflaged” as a female changes colours into the typical colouring of mating or spawning males. The animal, now clearly recognizable as a male, is tolerated by the female to swim into the spawning cave and release its sexual products near the eggs that have just been laid. This deliberate obtainig or steeling of reproductive success surreptitiously by way of camouflaged approaches to reproducing conspecifics is scientifically referred to as sneaking (BARLOW 2000; KEENLEYSIDE 1991; TABORSKI 1994; RÖMER 1998).

     Experimental work on various cichlid species from the East African Rift Lakes has shown, among other things, that under certain circumstances the vast majority of the offspring in some broods can stem from males known as sneakers (BARLOW 2000; HAESLER et al. 2009; KEENLEYSIDE 1991; TABORSKI 1994, 1998, 1999, 2008; RÖMER 1998). Corresponding observations on South American dwarf cichlids including Apistogramma have also been available for decades (RÖMER 1998). Reports about this from aquaristics, however, are rare, because, for obvious reasons, most enthusiasts keep their fish in pairs. The observations made on Apistogramma sp. “Mitu” can also consistently be interpreted in this way, although systematic studies are not yet available. Only comparative genetic examinations of the parents and their offspring will be able to provide exact information about this.

     After deposition of the approximately 50 to 80 red eggs, the male is tolerated only for a short time in the immediate surroundings of the cave. After that, the female completely takes over the vigorous defence of this area. For this purpose, immediately after the end of spawning, she continues to secure the entrance of the cave against potential intruders by piling up sand from the inside. Afterwards, in short trips all other fish are vigorously driven away from the area around the cave entrance.

Apistogramma sp. “Mitu”, female with fry. (Photo: Frank Hättich)

     The apparently polygamous males often spawn within a few days with the other females in the tank. At a water temperature of 25 °C, it takes about 60 hours from the laying of the eggs to the hatching of the larvae and a total of about 10 days until the fry is swimming free. Before swimming free, the larvae are sometimes transported by the female into one or even successively into several other caves – a behaviour known from numerous Apistogramma species (cf. RÖMER 1998, 2006). However, the deposit of larvae in sand pits outside caves or other hiding places, occasionally observed in other Apistogramma, has not yet been reported. Even weeks after free-swimming, the males are not tolerated in the immediate proximity of the fry by the brooding female let alone being involved in actually caring for them.

     Between egg-laying and the first free-swimming of the fry, the colouring of the females usually changes. The colouring pattern described above, indicating the maturity for spawning, intensifies towards an even more clearly contrasting pattern on a bright (lemon) yellow ground. At first the yellow colouring of body and fins is intensified, but the upper half of the body is still less strongly coloured than the lower half. In addition to the formerly already deep black frontal seams of anal and ventral fins, the first two to three dorsal membranes and the suborbital stripe, now some (or all) of the following black markings stand out more or less intensively from the yellow of the body and the fins in a mood-dependent combination or intensity: a) the lateral band, usually divided into several side spots or segments, b) the caudal spot, c) the dorsal spots, d) the supraorbital stripes, e) one spot each around the insertions of the ventral fins and f) exceptionally a short mid-ventral stripe in the area around the anus. ⁹  Endnote 9⁹ See the remark in endnote 8.
. Even if not involved in the brood-care themselves, some males also change their colouring after free-swimming of the fry. The frontal seams of the ventral fins as well as the frontal membranes of the dorsal fin then appear deep black, the seam of the anal is blackened, head and body as well as to a smaller extent also the fins take on a yellow-orange colouring while the red markings on the head fade almost completely.

     Among several brooding females, whose territories directly adjoined each other, naturally frequent conflicts at the territorial borders turned up. If the male became aware of this, it calmly swam with spread fins into the middle between both opponents. Often the fighting was stopped then. If the females turned out to be too aggressive, the male gave up his neutral attitude and drove one of them away from the territorial boundary, which immediately ended the quarrel. Which criteria it used to select which female was attacked remained unclear. Starting from the third week after free-swimming, the fry frequently changed between the territories of the brood-caring females by simply swimming into the adjacent territory and joining the corresponding swarm of fry. Although the females still vigorously defended their territories against each other, this behavior of the fry did not lead to increased conflicts between them. Attacks by females on young fish invading the territory could not be observed even if these belonged to other species (Apistogramma personata). There is some work available on the formation of swarms and the incorporation of other juveniles of the same as well as of different species into swarms by fish and in particular by Apistogramma females and the complex population biological causes responsible for this (BARLOW 2000; BROWN & DREIER 2002; KEENLEYSIDE 1991; LORENZEN 1989, 1990; MAGURRAN 1990, 2006; RÖMER 1998, 2001, 2006).

     After approximately five to six weeks, the juveniles are usually independent enough to completely and actively elude the female's care. If the female has lost the control over its fry, the male takes over the sovereignty over the brood-territory of the female again soon. In this phase, occasionally some juveniles fall victim to the male (observations UR). If the female is not ready to spawn again, it is expelled from the territory of the male for now. When kept in smaller aquariums, the juveniles should be transferred to a separate tank for further rearing in order to avoid losses.

Acknowledgements

We would like to thank Erik Bakker, Ernst van Genne, Roland Kipper, Yukitoshi Ohnota, Akihiro Shimizu, Satoshi Tanaka and Uwe Werner for valuable information and pictures they provided to us, and Roland Kipper for critically reviewing an earlier version of the manuscript.

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___________________________
¹ The choice of the trade name “Slender Gold”, instead of the less impressive designation “D6”, was probably made primarily due to the hoped-sales-promoting effect. However, it is not a pure fantasy name as it refers to two characteristics of the species. In both sexes of this slender species often a golden shimmering shine appears on the body, produced by the interplay of shining scales and the (also in males) frequently yellowish basic coloration of the body.
² Colombian spelling.
³ In the meantime identified to represent Apistogramma personata KULLANDER, 1980 (cf. RÖMER et al. 2017a)!
⁴ This consists of two parallel rows of vertical dashes offset to one another horizontally.
⁵ We hope that the examination of the genetic material of the offspring of the female in question will clarify this. Some preserved juvenile fish were kindly given to us for this purpose by Erik Bakker.
⁶ The fact that Apistogramma sp. “Mitu” can show a distinct lateral spot is remarkable, since the absence of it is considered to be a central differentiation criterion of the Apistogramma-regani-lineage from the three other lineages of the genus (KOSLOWSKI 2002, WISE in prep.). However, a concise lateral spot can also be observed regularly in breeding females of Apistogramma cf. alacrina (Guayas) (A108/D18), which also belongs to the Apistogramma-alacrina-group. As with numerous other criteria formulated for the systematization of the genus Apistogramma, it therefore appears that in this case too, it apparently is not an exceptional regularity.
⁷ An exception within the Apistogramma-alacrina-complex in this regard is Apistogramma sp. "Kiemenfleck/Gill-spot" (D37), which does not possess a lower pectoral spot (cf. HÄTTICH & OHNOTA 2018).
⁸ As already mentioned, it has not been clarified yet whether the only Apistogramma sp. “Mitu” female so far showing a mid-ventral stripe does not actually represent Apistogramma sp. “D53”.
⁹ See the remark in endnote 8.