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Growth characteristics and survival of Yellow perch Perca flavescens yolk-sac larvae at different temperature regimes

Three groups of yellow perch larvae were raised at constant temperatures of: 12º C (the optimal temperature for egg incubation), 15º C (the temperature was increased from 12-15º C over 6 hours post hatch) and 18º C (the temperature was increased from 12-18º C over 8 hours post hatch). For the fourth group the temperature was gradually increased from the incubation temperature at the rate of 1º C each day of the experiment. Larvae were raised in a closed recirculation system, within 500 liter conical tanks, at a stocking density of 80 larvae per liter. At 12º C, yolk sac resorption lasted for 152 hours, the mouth was open in 125 hours, and the first live food was found in the stomach 24 hours after the mouth opening. At the highest temperature of 18º C, the yolk sac was depleted in 124 hours, the mouth was open 96 hours after hatching, and the mouth became functional 20 hours after the mouth opening. At 15º C, the yolk sac was resorbed in 140 hours. In the fourth group in which the temperature was increased every day, the yolk sac was resorbed in 138 hours. The mouth was open 20 hours before yolk sac depletion in both groups, and become functional 22 hours after that. The relationship between the volume of the yolk sac and the time after hatching is shown in Table 1. The curve for the fourth group, where the temperature was increased during the experiment, showed the highest r2 value, but there was no significant difference in the regression curve characteristics among all four groups (ANOVA, P ≤ 0.05). The total lenght of larvae at the end of the experiment ranged from 6, 62±0, 22 mm at the temperature of 18 ºC, to 6, 66 ± 0, 22 mm at 15 ºC. Growth curves for different regimes didn't show any significant differences at P≤0, 02. Survival during the period of yolk sac resorption was 65% at the temperature of 18 ºC, what was significantly lower than in the other three groups where survival ranged from 78 – 86% (ANOVA, P≤0, 05). Table 1. Exponencial regresions describe resorption of the yolk sac in yellow perch, Perca flavescens, presented as a decrease in volume during the time after hatching. V, is the volume in mm² ; a, is the coeficient resorption proces ; time is given in hours.

Yellow perch; Perca flavescens; growht; survival; differetnt temperature; yolk-sac larvae

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