The use of tannic acid to remove adhesiveness from pikeperch, Sander lucioperca, eggs

Abstract

The studies conducted in 2003–2004 focused on the possibilities of applying a tannic solution to remove adhesiveness from pikeperch eggs. Spawners were caught in Lake Pątnowskie (central Poland) and then transported to the Goslawice Fish Farm. After initial selection, the fish were weighed, measured and stimulated with human chorionic gonadotropin. Gametes were obtained 5 days after the first injection. The weight and diameter of the eggs, and the commercial fecundity of individual females were determined. The eggs were fertilized with the dry method. After the addition of water, the eggs were mixed for 4 min, and then divided into 20 g portions. After determining the number of eggs in the various portions, the adhesiveness removal procedure was performed. Three concentrations of tannic acid solution (500, 1000, 1500 mg L−1) and three exposure times (0.5, 2, 5 min) were applied. The eggs were incubated in Weiss jars. The studies indicated that both the solution concentration and the exposure time significantly (P<0.05) impacted pikeperch egg hardening, the degree of adhesive removal and embryo survival. The tannic acid solution concentration of ≤500 mg L−1 applied for 0.5–2 min was not effective; the eggs clumped and it was impossible to separate them even with intensive mixing. Better results were obtained using higher tannic acid concentrations and/or by lengthening exposure time. The adhesiveness of pikeperch eggs disappeared completely after 5 min exposure to tannic acid solution concentrations of 500–1500 mg L−1 or after 2 min exposure to solution concentrations of 1000–1500 mg L−1. In these variants, the embryo survival rate to the eyed-egg stage was 78.0–84.0% (2003) and 82.3–84.7% (2004). However, high tannic acid concentration had a negative impact on the pikeperch larvae hatching. The greatest decrease in survival rate was observed in groups exposed to a tannic acid solution of 1500 mg L−1 for 2 and 5 min periods. Thus, the optimum method for removing pikeperch egg adhesiveness was to apply a solution of tannic acid at a concentration of 500 mg L−1 for 5 min or 1000 mg L−1 for 2–5 min.