The Effect of Increased Feeding in Proportion to Density on Sex Ratios in Zebrafish (Danio Rerio)

Abstract

The laboratory zebrafish (Danio rerio) is a biomedical model organism that can be commonly raised at different rearing densities across and within multiple facilities. Previous studies have shown how these rearing differences can be an important environmental factor attributed to sex skewed cohorts when fish reach maturation. When feed rations are not adjusted for density, especially within a facility composed of multiple stocking densities, the result is often a skewed sex ratio complicating further research. Therefore, the goal of this study was to determine if proportionally increasing food rations in high density tanks has an effect on correcting predominantly male biased outcomes. A baseline sex ratio was first established by raising ten tanks of an AB wild- type strain at a standard 10 fish per liter with a fixed food ration. Results show an even 50/50 outcome of males to females at maturation. Second, AB wild-type zebrafish were raised in five treatment groups all within an equally high rearing density of 40 fish per liter. Treatments were defined by the number of days post fertilization (dpf) each group remained at high density before returning to a standard density of 10 fish per liter. In increments of seven days, fish from a different treatment were redistributed to our standard density. The end result was five groups in triplicate, each spending a range of one week to five weeks post fertilization in a high-density environment. Food rations during these five weeks were adjusted for the proportion of fish housed in each tank. The results show that when food is appropriately adjusted for, raising fish in a high-density environment will not affect sex ratios up until four weeks post fertilization. Our findings also show that growth rates within the five treatments were not affected by rearing fish at 40 fish per liter for up to five weeks.