Evaluating the effects of tank color and environmental complexity on cisco phenotypes, coloration, and epigenomics

Andrew Honsey (USGS, ahonsey@usgs.gov), Clare Venney (U of Alberta), Trevor Pitcher (U of Windsor), Steve Davis (USFWS)

Captive rearing is an important component of restoration efforts for declining fish populations, including coregonines such as cisco (Coregonus artedi) in the Great Lakes. However, captive rearing often leads to unintended fitness and phenotypic effects on salmonids. For cisco, captive rearing is known to induce differences in body depth, facial morphology (i.e., pugheadedness), paired fin length, and gill raker counts. These phenotypic changes likely affect cisco survival in the wild. Captive environments often consist of barren tanks of an arbitrary color with minimal enrichment to make it easier to rear many fish at high density while keeping the tanks clean. Tank color is often overlooked, yet it can have drastic effects on fish color and phenotypes. Tank color also affects larval survival, weight, and cortisol levels, though the effect of different tank colors appears to be species-specific. In addition to the tank itself, substrate color can also influence fish coloration and aggression levels. These differences in tank and substrate color have been linked to differences in gene expression of behavioral and endocrine-related genes in various fish species and regulation of gene expression in cichlids and Chinook salmon (Oncorhynchus tshawytscha; T. Pitcher, unpublished data). Crypsis is an important anti-predator defense for juvenile fishes and a poor color match to their stocked environment could influence post-release predation and survival, particularly if fish are more conspicuous in the wild. Environmental enrichment can have positive effects on fish behavior and phenotypes, with positive implications for post-release survival. Several types of enrichment are possible, including vertical enrichment (e.g., PVC pipe structures) and substrate. Vertical enrichment can reduce metabolic rate, increase growth and survival, reduce cannibalism and aggression, and improve the ability of fish to deal with stress. In rainbow trout (O. mykiss), vertical enrichment led to substantial increases in total biomass and weight gain compared to barren tanks. The effects of environmental enrichment can have stable, positive effects on fish, and can even lead to positive effects on offspring neophobia and activity levels. The addition of substrate can also positively affect captive reared fish by reducing the frequency of skin abrasions and infections, as well as improving yolk sac conversion efficiency, potentially by increasing the amount of time spent resting on the substrate. Overall, environmental enrichment and tank coloration can have considerable, often positive effects on captive reared fish that could be harnessed to improve supplementation outcomes and improve survival in the hatchery and in the wild. Epigenomic mechanisms have been identified as a driver of animal coloration and other phenotypes induced by environmental enrichment. Epigenomic mechanisms, such as DNA methylation, affect gene transcription in response to the environment without a change in DNA sequence. DNA methylation is highly sensitive to the environment and has been repeatedly implicated as a mechanism contributing to the phenotypic and fitness effects of captive rearing. When epigenetic inheritance occurs, DNA methylation can also be passed on from parent to offspring, often leading to stable effects on phenotype even when offspring experience different environments than parents (i.e., wild offspring of captive-reared parents may continue to exhibit altered phenotypes). Thus, minimizing the epigenomic and phenotypic effects of captive rearing should be prioritized to maximize the success of conservation and supplementation efforts. Previous studies have suggested that modifying captive rearing protocols could help mitigate the epigenomic and phenotypic effects of captivity. We propose to investigate how early environment, specifically tank coloration and enrichment, affects cisco phenotypes and DNA methylation. If we observe previously reported morphological deformities such as pugheadedness, we will determine how these deformities influence performance. This will be the first study to investigate the effects of understudied captive rearing choices, such as tank color, on cisco, and it will serve as a springboard for future studies to evaluate the effects of captive rearing protocols on survival and predation in the wild (e.g., using acoustic telemetry and predation-sensing tags).