Effect of Turbidity Duration on Culture of Walleye Larvae

Abstract

Although turbid water is an essential environmental requirement for intensive larviculture of walleyes Sander vitreus on formulated feed, research has not determined the duration of turbidity required to achieve optimal benefits for survival and growth while reducing cannibalism. We conducted a replicated, single-factor analysis to determine the effect duration of turbidity on these performance indicators at 28 d posthatch (dph). Four treatments, each with three replicate 150-L tanks, involved culture of larvae in turbid water (84–125 nephelometric turbidity units [NTU]) from 3 dph to 7, 14, 21, or 28 dph. After culture under turbid conditions for the specified period, the fish were then cultured in clear water until 28 dph (i.e., fish in the 28-dph treatment received no clear-water culture). At 28 dph, substantial differences were observed in survival and growth among treatments. Fish survival for the 7- and 14-dph treatments (1% and 2%, respectively) was significantly less than that for the 21- and 28-dph treatments (11% and 14%, respectively). There was a significant difference in total length at 28 dph among the 7-, 14-, and 21-dph treatments but not between the 21- and 28-dph treatments. Fish in the 28-dph treatment were 177% heavier than those in the 14-dph treatment. A shift in phototaxic response at about 20 dph further reduced the need for turbid-water culture to prevent clinging behavior in walleye larvae. Cannibalism (2–5%) was observed in all treatments between 7 and 13 dph but not thereafter. The study substantiates benefits of turbid-water culture for larval walleyes and demonstrates that duration of turbidity should extend through 28 dph to maximize survival and growth but that it is less important for preventing cannibalism after 13 dph and clinging behavior after 20 dph.