Colour pattern and inhibition of aggression in the cichlid fish Astronotus ocellatus

Oscars Astronotus ocellatus defeated in combat often undergo a colour pattern change in which the normal olive-green to brown body coloration darkens to near black, interrupted with irregular white barring. Dummy oscars were used in two complementary tests which showed that the dark-and-banded colour pattern inhibits aggression in conspecifics under two different experimental designs and with two different subject groups.     

Mouth morphology, testes size and body size in male Tilapia zillii: implications for fighting and assessment

In Tilapia zillii , the outcome of fights is closely related to difference in testis weight between opponents rather than differences in body weight. Testes size was predictable statistically on the basis of the size of the mouth in relation to body size, suggesting that among other functions mouth morphology may have evolved to facilitate assessment during fighting.     

Histology of melanic flank and opercular color pattern elements in the firemouth cichlid,Thorichthys meeki

Dark melanic color pattern elements, such as bars, stripes, and spots, are common in the skin of fishes, and result from the differential distribution and activity of melanin‐containing chromatophores (melanophores). We determined the histological basis of two melanic color pattern elements in the integument of the Firemouth Cichlid, Thorichthys meeki. Vertical bars on the flanks were formed by three layers of dermal melanophores, whereas opercular spots were formed by four layers (two lateral and two medial) in the integument surrounding the opercular bones. Pretreatment of opercular tissue with potassium and sodium salts effectively concentrated or dispersed intracellular melanosomes. Regional differences in epidermal structure, scale distribution, and connective tissues were also identified. J. Morphol. 2013. © 2013 Wiley Periodicals, Inc.     

The benefits of uniparental versus biparental mouth brooding in Galilee St. Peter's fish

In Galilee St. Peter's fish Sarotherodon galilaeus the care system is naturally labile; biparental, male-only and female-only care all exist in one population. This unusual flexibility facilitates comparisons between the forms of care. The costs of parental care were considered in a previous study. Here, the benefits of parental care were quantified by observing wild fish, both held in pond enclosures and free-swimming in Lake Kinneret, Israel. Parental care was shown to be essential for offspring survival in St. Peter's fish. The reproductive success of parents who shared incubation duties was nearly twice as high as that of parents caring alone. However, per brood (or mouth cavity) reproductive success was 20% higher for uniparental parents. Both sexes were equally capable and efficient in care; when both sexes cared, they each incubated a similar number of eggs and released a similar number of fry. The results are discussed in terms of the relationship between caring Strategies and clutch size.     

Intraspecific brood adoption in the convict cichlid with respect to fry of two colour morphs

Convict cichlid Cichlasoma nigrofasciatum adults of the melanistic morph usually accepted fry of the same colour morph provided these were of approximately the same age and size as those of the receiver pair, whereas older and considerably younger fry were rejected or eaten. Xanthoric fry were usually accepted and rejected to the same extent as fry of their own colour morph. However, in certain combinations, especially when alien fry were 3 weeks old and the adopting parents already had their own 2 week old fry, fry of their own colour morph were significantly more likely to be adopted.     

Is speciation of demersal fishes in Lake Tanganyika restrained by physical limnological conditions?

Both Lake Malawi and Lake Victoria have many species of offshore demersal cichlids, most of which are stenotopic. In Lake Tanganyika there are fewer, more eurytopic, demersal species. These differences may be the effect of the physical regimes of the lakes. In Lake Victoria there is no permanent anoxic layer. In both the other lakes, water below 250 m depth is permanently anoxic and the seasonal cycle is dominated by upwelling. In Lake Malawi this is mainly derived from intermediate water containing free oxygen. In Lake Tanganyika upwelling involves hypolimnetic water, which may rise to within 80 m of the surface, causing great short-term changes in oxygen concentration over the depth range 50–250 m. This has inhibited the development of deep water species restricted to narrow depth ranges.     

The social and ecological costs of an ‘over-extended' phenotype

Extended phenotypes offer a unique opportunity to experimentally manipulate and identify sources of selection acting on traits under natural conditions. The social cichlid fish Neolamprologus multifasciatus builds nests by digging up aquatic snail shells, creating an extended sexual phenotype that is highly amenable to experimental manipulation through addition of extra shells. Here, we find sources of both positive sexual selection and opposing natural selection acting on this trait; augmenting shell nests increases access to mates, but also increases social aggression and predation risk. Increasing the attractiveness of one male also changed social interactions throughout the social network and altered the entire community structure. Manipulated males produced and received more displays from neighbouring females, who also joined augmented male territories at higher rates than unmanipulated groups. However, males in more attractive territories received more aggression from neighbouring males, potentially as a form of social policing. We also detected a significant ecological cost of the ‘over-extended'' phenotype; heterospecific predators usurped augmented nests at higher rates, using them as breeding sites and displacing residents. Using these natural experiments, we find that both social and ecological interactions generate clear sources of selection mediating the expression of an extended phenotype in the wild.     

Male mate preference and size-assortative pairing in the convict cichlid

Male convict cichlids Cichlasoma nigrofasciatum presented three females simultaneously were found to prefer larger females, even if a female's size exceeded their own. This indicates that some mechanism other than male choice, such as female choice or intrasexual competition, must contribute to male-larger assortative pairing in convict cichlids. Despite a preference for larger females, males continued to consort with smaller females when available, and a females attractiveness was a function of her size relative to other females.