Black color occurs in coloration of many freshwater fish beening relatively constant throughout the year and cryptic (in such, for example, bottom dwelling fish as wels, Silurus glanis). In this paper, we will consider those frequent cases when chiefly males of freshwater fish acquire black coloration in the reproductive period (nuptial melanization).

For desalinated areas and rivers of the Ponto-Caspian basin, five species of gobiid fish with nuptial melanization of body are most typical and abundant. Round goby, Neogobius melanostomus, monkey goby, N. fluviatilis, ratan goby, N. ratan, black goby, Gobius niger, and racer goby, Mesogobius gymnotrachelus, are among them. Gobies are marine origin, but the foregoing species (as well as many amelanistic species) inhabit desalinated areas and readily migrate into rivers of the Ponto-Caspian basin where successfully breed (Pinchuk et al., 1985; Romanesku, 2012). Some other euhaline gobies develop black nuptial coloration, such as giant goby, Gobius cobitis), but they avoid oligohaline bays and fresh waters.

In the reproductive period, gobies acquire conspicuous black coloration practically of the whole body using such an appearance, on the one hand, to repel rivals (in this case, black coloration is called threat, or antaposematic) and, on the other hand, to attract females (Trifonov, 1955; Yankovsky, 1966). Some gobies acquire color rims on the edge of both dorsal fins, pair pectoral and anal fins: white in N. melanostomus, yellow in M. gymnotrachelus and orange in N. fluviatilis. In accordance with the accepted terminology (Trifonov, 1955; Yankovsky, 1966), these conspicuous color signs are called gamosematic, bacause these signs appear in males when they prepare the nests, indicating in this way on their readyness to breed, and disappear in males when they begin to protect the nests with laying eggs.

Spawning and nest guarding in N. melanostomus are well documented (Meunier et al., 2009).

In general, round goby, N. melanostomus, and other gobies are rather visually guided fish with the specialized chemoreceptory channel. N. melanostomus respond poorly to the odors of lake whitefish (Coregonus) tissues, crushed dreissenids and fish eggs (Sreedharan et al., 2009; Yavno & Corkum, 2011). At least Sreedharan et al. (2009) do not recommend to use food-baited traps to control the spread of these fish. According to Rollo et al. (2007), N. melanostomus have well developed vocalization and are attracted by conspecific calls in both laboratory and field trials.

Nuptial melanization is also found in such fish of the North American ichthyofauna as dirty darter, Etheostoma olivaceum, Gila topminnow, Poeciliopsis occidentalis, and Olympic mudminnow, Novumbra hubsi (Kodric-Brown, 1998). Coloration of males in brook stickleback, Culaea inconstans (Ward & McLennan, 2006), mosquitofish, Gambusia holbrooki (Horth, 2004) and Amur sleeper, Percottus glehni (Tsepkin, 1977), are other examples of nuptial melanization.

Interestingly, in mosquitofish, G. holbrooki, black males have advantages and disadvantages to more common silver rivals. On the one hand, largemouth bass, Micropterus salmoides, crayfish (Procambarus) and dragonfly larvae (Libellulidae) prefer, as natural predators, silver males (Horth, 2004), that is black males are under less predation pressure. According to Taylor et al. (1996), on the other hand, females of G. holbrooki prefer silver males and even can avoid black males.

Basic References

Horth L. 2004. Predation and the persistence of melanic male mosquitofish (Gambusia holbrooki). Journal of Evolutionary Biology 17, 672-675

Kodric-Brown A. 1998. Sexual dichromati ... Read more »

Conspicuous coloration of males occurs in many species of fish, birds and other animals being advantageous in attracting potential mates. Although bright colors can entice females of the same species, these colors may also attract predators. Female choice for bright males and an enhanced risk of predation for bright males are both well documented in numerous works (see Dill et al., 1999, and references therein).

Because fresh waters are optically turbid in comparison with pure sea waters, curves of photopic spectral sensitivity in freshwater fish are strongly displaced to the red part of the spectrum. For example, the maximum of spectral sensitivity in threespined stickleback, Gasterosteus aculeatus, is near 605 nm (Rowe et al., 2004). It means that for eyes of freshwater fish red and orange colors are brighter than all other equipower monochromatic colors, and this feature occurs in nuptial signaling coloration.

The nature allows males of freshwater fish to practice several strategies to find trade-offs between conspicuousness for sexual mates and crypticity for potential predators, including plasticity in nuptial color development (e.g., Endler, 1983; Candolin, 1998; Ruell et al., 2013). In this context, an ability to develop bright red and orange colors in the under less illuminated parts of the fish’s body, in conformity with the theory of color countershading in fresh waters, is the primary.

Indeed, red and orange colors occur in breeding males just in the under parts of their bodies such as breast, ventral part, belly and the lower fins. An important role of this elements in nuptial coloration of males is documented in guppy, Poecilia reticulata (Endler, 1983; Kodric-Brown, 1985), and other species of genus Poecilia, threespined stickleback, G. aculeatus (Rowe et al., 2004), European bitterling, Rhodeus sericeus (Candolin & Reynolds, 2001), and in other spesies of genus Rhodeus, as well as in males of other freshwater fish. In some cases red and orange colors occur in the upper most illuminated parts of the fish’s body, but patterns of this type will be considered separately.

According to Kodric-Brown (1998), breeding males with red fins occur in many families of North American freshwater fish, including minnows (Cyprinidae), suckers (Catostomidae), killifish (Fundulidae), sunfish (Centrarchidae), darters (Percidae) aa well as cichlids (Cichlidae).

Generally, bright red and orange colors are conspicuous at the shot distance for sexual mates, but are cryptic in the countershading complex at the longer (that is optically thick) distances for potential predators. According to Evans & Norris (1996), red pigmentation of the fish’s body cannot be assessed accurately under green light or hereof if viewed through the water column, as the natural green filter.

Vorobyev et al. (2001) demonstrate how fish can see other fish through the water column.

Basic References

Candolin U. 1998. Reproduction under predation risk and the trade-off between current and future reproduction in the threespine stickleback. Proceedings of the Royal Society, Biological Sciences 265, 1171-1175

Candolin U., Reynolds J.D. 2001. Sexual signaling in the European bitterling: females learn the truth by direct inspection of the resource. Behavioral Ecology 12, 407-411

Dill L.M., HedrickA.V., Fraser A. 1999. Male mating strategies under predation risk: do females call the shots? Behavioral Ecology 10, 452-461

Endler J.A. 1983. Natural and sexual selection on color patterns in poeciliid fishes. Environmental Biology of Fishes 9, 173-190

Evans M.R., Norris K. 1996. ... Read more »

Brightly colored males of freshwater fish are forced to find trade-offs between conspicuousness for sexual mates and cripticity for potential predators. Divergence in spectral sensitivity of prey and predators is one of the possible ways to solve this problem in its evolutionary development.

The maximums of spectral sensitivity in threespined stickleback, Gasterosteus aculeatus (605 nm: Rowe et al., 2004), as prey, and perch, Perca fluviatilis (635 nm: Protasov, 1968), as natural predators, are strongly distanced. It means that for P. fluviatilis, as specialized observers in the longwave part of the spectrum, bright red breast and blue iris of G. aculeatus (Rowe et al., 2004) must look darker (that is cryptic) than for the owners of these colors. Similarly, the maximums of spectral sensitivity in pumpkinseed sunfish, Lepomis gibbosus (612 nm: Tamura & Niwa, 1967), as prey, and largemouth bass, Micropterus salmoides (673 nm: Kawamura & Kishimoto, 2002), as natural predators, are distanced even more. So, for M. salmoides, with fine color vision in the far red part of the spectrum, conspicuous red iris and opercular flaps, all-important for breeding sunfish (Stacey & Chiszar, 1978), must be dimmer than for the sunfish exploited these signals.

Another way is the divergence of spectral sensitivity in the shortwave part of the spectrum.

Vision in the ultraviolet (UV) part of the spectrum (with the maximum of spectral sensitivity near 365 nm) affects female mate choice in threespined sticklebacks, G. aculeatus (Rick et. al., 2004; Boulcott et al., 2005; Rick et al., 2006). According to Leech & Johnsen (2009), however, ability to see in the UV region (with the maximum near 385 nm) occurs only in planktivorous individuals of Perca flavescence (or P. fluviatilis) disappearing in adult predatory fish.

Basic References

Boulcott P.D., Walton K., Braithwaite V.A. 2005. The role of ultraviolet wavelengths in the mate-choice decisions of female three-spined sticklebacks. Journal of Experimental Biology 208, 1453-1458

Kawamura G., Kishimoto T. 2002. Color vision, accomodation and visual acuity in the largemouth bass. Fisheries Science 68, 1041-1046

Leech D.M., Johnsen S. 2009. Light, Biological Receptors. Encyclopedia of Inland Waters. (Gene E. Likens, Editor), Oxford, Elsevier. Volume 2, 671-681

Protasov V.R., 1968. Vision and near orientation in fish. Israel program for scientific translations, Jerusalem

Rick I.P., Modarressie R., Bakker T.C.M. 2004. Male three-spined sticklebacks reflect in ultraviolet light. Behaviour 141, 1531-1541

Rick I.P., Modarressie R., Bakker T.C.M. 2006. UV wavelengths affect female mate choice in three-spined sticklebacks. Animal Behaviour 71, 307–313

Rowe M.P., Baube C.L., Loew E.R., Phillips J.B. 2004. Optimal mechanisms fo finding and selecting mates: how threespine sticklebac ... Read more »

Countershading is an examplary pattern of animal coloration in which an animal’s pigmentation is darker on the upper side and lighter on the under side of the body. When light falls on any volume uniformly colored object from above, it makes the upper side appear lighter and the under side darker with the gradual transition between them. Thanks to the counetrshading with the dark upper side and the light under side, the same object appears flat and thus invisible on the surrounding background.

This basic pattern is found in many species of mammals, reptiles, birds, fish and other animals.

Color countershading is determined by color vision of fish that is characterized by the different bell like curves of spectral sensitivity. Spectral sensitivity is an ability of the eye to perceive monochromatic light of equal power with the different wavelengths. Eyes of saltwater fish, and human, are most sensitive to light with the wavelengths of 550-560 nm (the green-yellow part of the spectrum). Because fresh waters are optically turbid, eyes of freshwater fish are more sensitive to light with the wavelengths of 600-680 nm (the orange-red part of the spectrum). Due to bell like dependence of spectral sensitivity equipower monochromatic light of different wavelengths are not equally bright to the eye. Green light is most bright for human and saltwter fish, red light is most brigth for freshwater fish contrary to our perception.

In the terms of cryptic countershading, coloration of freshwater fish may be conditionally divided into achromatic, or bright countershading patterns and chromatic, or color countershading patterns. Greyish back, silver (mirrored) sides and whitish belly are typical for fish with the achromatic countershading. Green, yellow (goldish or golden), orange and red colors are main components of the color countershading patterns. Darker colors lie on the top, brighter colors lie on the bottom with the corresponding gradual transitions. The first sign of the presence of color countershading in an appearance of freshwater fish is red color of pectoral, pelvic, anal and caudal fins lied in the less illuminated parts or in the shadow of the fish’s body.

Pelagic Coloration

In general, coloration of freshwater pelagic fish is ranged from blank achromatic countershading patterns to color countershading patterns, depending on the optical properties of the water.

For idealized mixed countershading patterns, greenish back, silver sides, whitish belly as well as yellowish, orange, reddish or red pectoral, pelvic, anal and caudal fins are typical. This type of coloration is found in European asp, Aspius aspius, Aral redlip, A.a. taeniatus, in many Amur fish (see Nikolski, 1956) like Amur redfin, Pseudaspius leptocephalus, skygazer, Erythroculter erythropteru ... Read more »

According to Walker & Hasler (1949), trained bluntnose minnow, Hyborhynchus notatus (Pimephales notatus) are able to discriminate rinses of the following pairs of aquatic plants: Myriophyllum exalbescens and Ceratophyllum demersum, Ranunculus trichophyllus and Anacharis canadensis, Utricularia vulgaris and Vallisneria americana, Potamogeton zosteriformis and P. cripus, P. amplifolius and P. vaginatus as well as Chara excelsa and P. pectinatus. Of 12 plant species tested, only rinses with odors of C. demersum and A. canadensis resemble each other.

Figure 1. Bluntnose minnow, Pimephales notatus (powered by Joseph Tomelleri)

The threshold of chemosensitivity to odors of aquatic plants is at the level of 1:10000 dilution (Walker & Hasler, 1949), plus additional dilution in the test aquarium that demonstrates overall very high odor sensitivity.

Rinses of Cabomba caroliniana, Sparganium sp., Utricularia vulgaris, Nuphar variegatum and Potamogeton epihydris are attractive for migrating elvers of American eel, Anguilla rostrata (Sorensen, 1986). However, the attractivity of these rinses is exceptionally determined by epiphytic bacteria, fungi and algae that are abundant on the most species of aquatic plants.

Rinses of seaweeeds, Ascophyllum nodosum and Laminaria saccharina, repel elvers (Sorensen, 1986).

Finally, rinses of decaying leaf detritus are highly attractive to elvers regardless of where detritus is collected (Sorensen, 1986). In contrast, rinses of living and fallen leaves collected from the forest floor are not attractive.

Basic References

Sorensen P.W. 1986. Origins of the freshwater attractant(s) of migrating elvers of the American eel, Anguilla rostrata. Environmental Biology of Fishes 17, 185-200

Walker T.J., Hasler A.D. 1949. Detection and discrimination of odors of aquatic plants by the bluntnose minnow (Hyborhynchus notatus). Physilological Zoology 22, 45-63