Successful Rearing of Nutritionally Supplemented Rotifers (Brachionus plicatilis) at Reduced Salinity for Zebrafish (Danio rerio) Polyculture

Abstract

Rotifers, Brachionus plicatilis, are a valuable first exogenous feed for zebrafish because they can provide continuous nutrition for growing zebrafish larvae when used in a rotifer-zebrafish polyculture. Typically cultured at high salinities (>10 ppt), B. plicatilis are temporarily immobilized when moved to lower salinities (5 ppt) used for polycultures, decreasing their accessibility and attractiveness to the larvae. The nutritional value of rotifers varies based on their diet, typically live algae, which has limited nutritional value and may pose biosecurity risks. After confirming that rotifers consume and can reproduce when fed an irradiated, processed larval fish diet (PD), they were reared at 5 or 15 ppt, and fed various combinations of an algae mix and/or PD. Population densities and percentages of egg-bearing rotifers were quantified daily until the population density plateaued, and then their nutritional value was assessed. Results indicated that rotifers thrived at both salinities. Those fed PD were successfully maintained at >500 rotifers per mL and contained a greater ω-6/ω-3 fatty acid ratio. Our findings indicate that enriching rotifers with PD raised at 5 ppt can potentially eliminate rotifer immobilization in polyculture, while providing a nutritious, attractive diet for zebrafish larvae and decreasing biosecurity risks.

Keywords: Brachionus; husbandry; polyculture; rotifers; zebrafish.

FIG. 1.

Comparison of population growth dynamics. (A) Experimental groups used to determine the optimal dose of the processed larval fish diet (PD) and frequency of water exchanges. (B) Experimental groups used to compare population growth dynamics and nutrition in rotifers fed PD, A, or a combination of PD and A at salinities of either 5 or 15 ppt. PD, processed diet; A, algae.

FIG. 2.

Temporal distribution of the mean population density of rotifer subcolonies fed a larval fish PD at 0.36 g, 0.48 g, or 0.60 g per million rotifers daily with either daily or every other day water exchange.

FIG. 3.

Population of rotifer subcolonies fed a larval fish PD at 0.36 g, 0.48 g, or 0.60 g per million rotifers with daily or every other day water exchanges. Results are the mean across all time points ± the standard error. * and ^# denote statistical significance (p < 0.05) between indicated groups.

FIG. 4.

Temporal distribution of the mean population density of rotifer subcolonies raised at 5 ppt and 15 ppt and fed a larval fish PD, A, or a combination of PD and A.

FIG. 5.

Mean ± standard error of daily population densities of various feeding and salinity groups for the entire period during which the subcolonies were maintained. PD denotes larval fish processed diet; A denotes algae. *, **, ***, ****, and ***** denote statistical significance (p < 0.01) and ^# (p < 0.05) between similarly identified groups.

FIG. 6.

Temporal distribution of mean ratio of egg-bearing:barren rotifers in subcolonies raised at 5 ppt and 15 ppt and fed a larval fish PD, A, or a combination of PD and A.