Intensive culture of walleye larvae produced out of season and during regular season spawning

The performance of larval walleyes Stizo-stedion vitreum that were produced out of season was compared with larvae produced during a regular season, using intensive culture methods. Wild-captured walleye adults were held in an earthen pond beginning in late November and then gradually transferred to higher water temperatures before ovulation was hormonally induced in February. A second batch of walleye larvae was obtained from a hatchery operation in April and otherwise reared in similar conditions. The two experiments were conducted to evaluate survival and growth of walleye larvae reared initially on live nauplii of brine shrimp Artemia salina and then gradually weaned to commercial diets. Larvae were stocked at 20 fish/L and raised in large (800-L) triplicate tanks provided with turbid water (40-50 nephelometric turbidity units) and surface sprays. Mean final weight of fish after 32 d of rearing from the first (February; 100.5 ± 17.5 mg) and second (April; 111.2 ± 18.0 mg) batch did not differ significantly, whereas survival was 6 ± 1.9% for juveniles produced out of season and 47 ± 1.6% for those produced during the regular season. The lower survival rate obtained with out-of-season juveniles can be attributed to somewhat altered egg quality, slightly different dietary regimes, and other physical variables. As these variables are optimized, the ability to sequentially wean two cohorts of juvenile walleyes to commercial diets in the same facility, while producing a 5-week growth advantage to one cohort, may become of significance to aquaculture.