Effect of dietary supplements of mussel and polychaetes on spawning performance of captive sole, Solea solea (Linnaeus, 1758)

Three diets were compared for the feeding of captive common sole broodstock (Solea solea) kept under ambient photoperiod and temperature conditions. A group of 70 adults were caught in the wild and the 38 males and 32 females distributed at random in six tanks. All the fish were acclimated to the same semi-moist diet (M) in the pre-experimental period from December to February. Three dietary treatments were offered in the experimental period from March to May with two replicates (tanks) per treatment. The treatments were M alone, M supplemented with fresh mussels (Mytilus edulis) (M + M), and M supplemented with live polychaetes (Perinereis cultrifera) (M + P). Spawning occurred during April and May when water temperature was 17 and 18 degrees C, respectively, and salinity around 34-35 ppt. Average daily dry matter intake expressed as a proportion of body weight was M 0.65 +/- 0.34%, M + M 0.43 +/- 0.18%, and M + P 0.56 +/- 0.27%, and differed significantly (P < 0.05) between treatments. The average daily dry matter intake within a tank ranged from 0.31 +/- 0.04% in February to 0.98 +/- 0.26% in May (P < 0.05), apparently due to changes in the photo-thermal regime. Diet significantly affected the number of days when spawning occurred, the number of days when hatched eggs were produced, and the proportion of fertilized eggs (P < 0.05); and affected the number of days on which viable eggs were produced during April (NS). In all cases, the results were lowest for M + M, while those for the other two treatments did not differ significantly. Differences in hatching rate were not significant in April. During May, no spawning occurred in fish given the M + M treatment, and the differences between the other two treatments were not significant. Values for all variates tended to be higher for M + P than M + M in April and lower for M + P and M in May. These results suggest that supplementing the semi-moist diet with mussels depressed feed intake and, consequently, reproductive performance: the semi-moist diet alone and semi-moist diet supplemented with polychaetes allowed satisfactory food intake and reproductive performance in broodstock sole.