Survival and growth of walleye Stizostedion vitreum fry as affected by water recirculation, feed transition age, and stocking density

The effects of recirculation aquaculture on walleye Stizostedion vitreum fr y culture was evaluated from hatch (day 0) to day 65 and compared to tradit ional flow-through aquaculture used at New York State's Fish Culture Statio n. Oneida. New York. USA. A comparison of survival rates of walleye fry thr ough a feed transition period was also conducted with the variable being th e age (d) at which dry feed was first introduced to fingerlings: this trial was conducted using recirculation aquaculture systems only. Comparisons we re made of growth rates and survival rates broken down into two life stages : stage one was from day 0 to day 45 and stage two from day 45 to day 65. A ll systems were taken off live feed completely on day 45 resulting in a fee d transition period between days 45 and 65. Fish in the how-through system had the highest cumulative growth rates through day 70 (P < 0.05) while fis h in the recirculating system grew faster through day 53 (P < 0.10). The re circulating system showed significantly higher survival rates during the fe ed transition period (day 45-65) than fish in the conventional flow-through system (P < 0.05). This is important because the transition period is the most stressful period in training fingerlings onto dry feed from a live die t. It was found that fish started on a dry diet on day 1 or day 14 in addit ion to the live diet had a significantly higher survival rate through the f eed transition period than fish started on dry feed on day 30 (P < 0.1). Th e age at which dry feed was introduced had no significant impact on growth rates. There was a significant positive correlation (P < 0.05) between surv ival rates and the initial stocking density over a range of densities from 3,500 to 7.000 fish/m(3).