A refuge population of Delta Smelt has been cultured in a conservation hatchery (Byron, CA) since 2008 to help protect the imperiled species from extinction. Culture techniques for this population have thus far focused on maximizing genetic diversity and fish production, which includes rearing multiple families within the same tanks. However, Delta Smelt production, associated research projects, and related conservation measures would benefit from also being able to rear fish on a smaller scale, such as in individual family groups. Accordingly, new culture systems and protocols have been developed for rearing small numbers of Delta Smelt embryos (3-10 days post-fertilization), early-stage larvae (0-40 days post-hatch, dph), and late-stage larvae (40-80 dph).
We evaluated the performance of these small-scale culture systems across two studies. In Tsai et al. (2022), we found that the hatching rate of embryos incubated in a small-scale system did not differ from that of embryos incubated in standard facility systems. Early-stage larvae reared in a small-scale system did not differ in survival rate, but were longer and heavier than facility-reared larvae. In contrast, late-stage larvae reared in a small-scale system had lower survival and were shorter and lighter than facility-reared larvae. To help identify the cause of poor late-larval outcomes, we conducted a second study examining the effects of stocking density on the survival, length, and weight of late-stage larvae reared in a small-scale system (Tsai et al. Submitted). We found no effect of density on any of these measures and therefore could not identify the reason for the poor performance of late-stage larvae in the first study. However, across all densities, the survival and size of larvae reared in Tsai et al. (Submitted) did not differ from that of facility-reared larvae (Tsai et al. 2022). Thus, with optimization of rearing protocols (Tsai et al. Submitted), the small-scale systems are effective in culturing Delta Smelt from embryo to 80 dph. Based on these results, we will expand the development of small-scale Delta Smelt culture to include juvenile and adult life stages.