Continued Embryonic Development, Survival, and Growth of Walleye Larvae Following Exposure to Dewatering and Storage in Melting‐Ice Temperatures

Abstract

The tolerance of eyed‐stage embryos of Walleye Sander vitreus to cooling at melting‐ice temperatures and their subsequent hatching and rearing to advanced juveniles were examined. Embryos (71% viable; 8 d after fertilization) were refrigerated in an insulated transportation Styrofoam box between wet cheesecloth layers and melting ice (1.4°C) for 25, 48, 72, and 120 h. Embryos were then acclimated to 14°C aquaria for hatching and rearing (20°C). The hatching of embryos and their ability to continue development (swim bladder inflation), food acceptance (live nauplii of brine shrimp Artemia spp.), and growth were monitored for 14 d. The duration of exposure to cold storage stress resulted in no significant differences in mean ± SD survival (46.8 ± 8.0, 38.7 ± 8.6, 41.0 ± 4.9, and 36.9 ± 12.5% for 25‐, 48‐, 72‐, 120‐h treatments, respectively) at the end of the rearing and feeding period. However, the proportion of fish with inflated swim bladders was the highest in the 120‐h cold‐delayed fish (mean ± SD = 61 ± 18, 54 ± 8, 64 ± 3.8, and 90.5 ± 8%, respectively). The mean weight of fish was not significantly influenced by cold storage treatments but was significantly influenced by swim bladder status (9.2–11.8 mg, 7.0–9.8 mg, and 5.7–9.5 mg for fully inflated, partially inflated, and uninflated groups, respectively). This experiment provides significant new data to fish culturists regarding the storage of Walleye embryos prior to hatching and the possibility of convenient transportation or delayed stocking of larvae into prepared nursing ponds or indoor rearing tanks for intensive culture.