Performance of Larval Walleye Cultured Intensively in Clear and Turbid Water

Experiments were conducted to determine the performance of larval walleye (Stizostedion vitreum) reared in clear, 0.2 nephelometric turbidity units (NTU), and turbid water, 20 or 50 NTU, on formulated feed. Larvae were cultured for 21, 28, or 30 days posthatch in four trials with 3 or 4 replicate tanks per treatment (clear and turbid) in each trial. Duration of each trial was dependent on the arrival of newly hatched larvae for subsequent trials. The desired turbidity levels were obtained by pumping a solution of clay to the culture tanks every 20 (trial 1) or 30 min (trials 2, 3 and 4). Other than turbidity, all environmental conditions (dissolved oxygen, alkalinity, pH, total ammonia, un-ionized ammonia, nitrate, nitrite, chloride, and hardness) and rearing techniques were similar between treatments. Larvae were stocked at 20/L and fed formulated feed (Fry Feed Kyowa B-400 and B-700) every 3 to 7 min, 24 hours per day. Significant differences in feed acceptance and total length between larvae in the clear and turbid water were observed as early as 7d posthatch. Larvae in turbid water began eating the formulated diet one to two days before those in clear water. In all trials, survival, final length, and final weight of larvae reared in water of high turbidity were significantly greater than for larvae reared in clear water. Mean survival (±SE) for all four trials was 27.7 ± 5.6% in high turbidity water and 5.9 ± 1.3% in clear water. At the end of the trials, mean total length of the larvae reared in turbid water was at least 3.2mm (15%) greater than that in the clear water. Mean final weight of the larvae from turbid water was 2.25 times greater than larvae from clear water over the four trials. In two of the four trials, gas bladder inflation (GBI) of larvae reared in high turbidity was significantly greater than for fish reared in clear water, but the difference in GBI was not significant in the other two trials. In this study, performance of larval walleye was greatly enhanced by water with a turbidity of at least IS NTU.

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