Phillips, T.A., Summerfelt, R.C.
Abstract:
In two previous studies, it was demonstrated that walleye cultured in
turbid water commenced feeding at an earlier age, they grew faster,
they had a lower incidence of cannibalism, but improved gas bladder
inflation and greater survival to 21 to 30 days than walleye raised in
clear water. Turbidity reduced clinging of fry to the tank walls and
improved feeding. Turbidity levels used in those experiments ranged
from 16.1 to 49.7 nephelometric turbidity units (NTU), but optimum
and maximum limits of turbidity were not evaluated. The present
study was undertaken to determine optimum turbidity level and to
determine whether high levels of turbidity (i.e., 100-300 NTU) reduce
survival and growth.
Two experiments (E1 and E2) were conducted. In each experiment,
six treatment turbidity levels were evaluated: clear (0.8), 12, 26, 54,
100, and 206 NTU in E1 (the NTU values correspond to estimated
suspended solid concentrations of 2.7, 15, 35, 70, 120, and 250
mg/L); and clear (0.5), 91, 144, 182, 227, and 295 in E2 (estimated
suspended solid concentrations of 2.3, 115, 180, 220, 280, and 360
mg/L). Turbid water was prepared by addition of small quantities of
commercial kaolinite clay (76% of the particles <2.0 micro m). We
also examined gills histologically for epithelial lifting, necrosis,
lamellar fusion, hyperplasia, and clubbing.
In E1, survival to 28-d posthatch was highest at 206 NTU and no
walleye survived in clear water (0.8 NTU) after 22-d (Table 4). In E2,
survival to 28-d posthatch was highest in the 182 NTU treatment. In
both experiments, survival-turbidity curves when fish were 28-d
posthatch were parabolic: maximum survival was 46% at 164 NTU in
El, and 34% in E2 at 200 NTU. Length-turbidity curves were also
parabolic at 28d: maximum total length was 22 mm at 150 NTU in E1
and 27 mm at 200 NTU in E2. No histological alterations were
observed in gills of any fish raised in turbid water.
The results confirm previous findings that turbidity is beneficial to
intensive culture of walleye fry. Optimum concentrations for survival
and growth range from 150-200 NTU. Upper limits, that is levels that
may adversely affect survival and growth are in excess of 295 NTU
(360 mg/L suspended solids), but survival and growth at even the
highest concentration (295 NTU) was greater than in clear water, or
turbidities <100 NTU. The present and previous experiments indicate
that turbid water provides a beneficial environment for intensive
culture of walleye for the first 30-days of life.
(Department of Animal Ecology, Iowa State University, Ames, Iowa
50011-3221 USA)