# Different Colours, Different Outcomes: Tank Colour Shapes Larval Survival, Growth, and Endocrine Response in Cichlasoma dimerus

## TL;DR

The color of fish tanks affects how cichlid larvae grow, survive, and develop hormonally, with white tanks leading to higher weight but lower survival.

## Contribution

This study reveals that tank color significantly influences larval fish development, including survival, growth, and endocrine traits.

## Key findings

- White tanks resulted in lower survival but higher body weight in cichlid larvae.
- Tank color affected hormone-related traits like somatolactin and growth hormone responses.
- White tanks showed a female-biased sex ratio and altered nuclear and cytoplasmic areas in hormone cells.

## Abstract

Conditions experienced early in life can strongly influence how fish grow, survive, and develop. One factor that is often overlooked in fish rearing is tank colour. In this study, we examined how tank colour affects the development of larvae of the cichlid fish Cichlasoma dimerus. Larvae were reared in white, light-blue, or grey tanks, and we evaluated survival, growth, pigmentation, skeletal development, sex ratio, and hormone-related responses. We found that larvae reared in white tanks had lower survival but reached a higher body weight compared with those reared in the other colours. Tank colour also affected hormone-related traits linked to growth and skin pigmentation, although skin pigmentation itself did not differ among treatments. Skeletal development followed the expected pattern across all colours, and a higher proportion of females was observed in white tanks. Overall, these results demonstrate that tank colour influences multiple aspects of fish development and should be considered when optimizing early-life rearing conditions, fish welfare, and experimental design.

Early environmental conditions play a critical role in shaping fish physiology and behaviour, with tank colour emerging as a relevant yet often overlooked factor in aquaculture and experimental research. This study investigated how rearing tank colour affects larval performance in the cichlid fish Cichlasoma dimerus. Larvae were reared in white, light-blue, or grey tanks, and survival, growth, pigmentation, sex ratio, skeletal development, and the endocrine responses of somatolactin (Sl) and growth hormone (Gh) were evaluated. Survival was significantly lower in white tanks. Conversely, larvae reared in white tanks reached a higher final body weight, while total length showed a similar but non-significant trend. Gh-immunoreactive cells exhibited significantly larger nuclear areas in larvae reared in white tanks and a tendency toward smaller cytoplasmic areas compared with those from light-blue tanks. Melanophore number did not differ among treatments, whereas larvae from grey tanks showed a higher number of Sl-immunoreactive cells. Sex ratios tended to be female-biased in white tanks. Skeletal development did not differ among tank colours and followed the expected chondrogenesis and ossification sequence. Overall, tank colour influenced multiple aspects of larval development, particularly survival, growth, and endocrine responses, underscoring its relevance in fish rearing and experimental design.