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The variable colour patterns of Tilapia zillii (Cichlidae): integrating ethology, chromatophere regulation and the physiology of stress
Hulscher-Emeis, T.M. (1992). The variable colour patterns of Tilapia zillii (Cichlidae): integrating ethology, chromatophere regulation and the physiology of stress. Neth. J. Zool. 42(4): 525-560
In: Netherlands Journal of Zoology. E.J. Brill: Leiden. ISSN 0028-2960, more
Peer reviewed article  

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Keywords
    Brackish water; Fresh water

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  • Hulscher-Emeis, T.M.

Abstract
    Tilapia zilii, a substrate cichlid fish, practising bi-parental care, displays variable colour patterns during social behaviour. This study aims at gaining more insight in the causation of social behaviour through ethological analysis of these displays. The colour patterns are composed of a restricted number of, idepedently modifiable, melanistic marking elements (MEs) in the skin of body and fins, which can contrast or blend with the greyish-silver ground colour, that in its turn is variable. Histological survey shows that melanophores and light-reflecting chromatophores are unequally distributed in the skin. Differential regulation of the chromatophores can explain the variability of colour patterns. The MEs develop during ontogeny in the semi-transparent larvae. Initially the melanophores, being continously in the dispersed state, effectuate crypsis. After development of the ground colour, later in ontogeny, variability of the MEs becomes apparent. Next to crypsis, other aspect of the colour patterns in relation with the contextual situation then start playing a role in social behaviour.The variable black markings do not relate directly with attack or escape tendencies. A particular ME becomes visible when an inclination to maintain a specicfic spatial position is activated and, concomitantly, the fish is endangered (falls into a 'perturbed sate'). The greatar the unreliability of current events, the darker the MEs become. Thus 'pertubed state' harbours both cognitive characteristics and 'conflict': a discrepancy between the existising situation and a reliable one. Since the same physiological factors underlyning the regulation of melanophers are involved of stress, the results open prospects towards ethological implications of stress.

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