The influence of cage culture of the mullet Lisa haematocheilus (Temminck & Schlegel,1845) on biochemical composition of their eggs

The Far Eastern haarder Lisa haematocheilus (Temminck & Schlegel, 1845) is considered as one of the most promising aquaculture species in the southern seas of Russia. Despite the fact that this species have become naturalized in the Azov and Black Sea basin, the development and improvement of biotechnologies on artificial breeding and cultivation remain an urgent problem. Not only meat but also roe of haarder is of great commercial interest because caviar is regarded as a gourmet product. It is known that rearing conditions, especially diet, influence the chemical composition of an organism as determined by its adaptation to new conditions. To assess the effect of cage culture with our own compound feed formulation used, a comparative analysis has been done of the biochemical composition of eggs of the Azov Sea haarder raised in cages that were installed in the adjacent estuary.

The studies have shown that the water concentration and lipid content in the eggs of caged fish were, respectively, by 30% and 28% more than in the eggs of wild fish (Р<0,05). Differences in protein and mineral fractions were minor.

Greater accumulation of triacylglycerols (by 60% more) and phospholipids (by 19% more) is observed in the eggs of farmed fish than in the wild haarder roe (P <0.05). The levels of other lipid fractions were similar enough. There were no significant differences in the phospholipid spectrum of eggs of both groups.

The main differences in fatty acids were associated with docosahexaenoic acid, its concentration was 1.4 times higher in wild fish, while linolenic and eicosadienoic acid levels were 1.6 times lower than those of the caged fish.

Despite some differences in the relative content of both individual and a group of saturated, monoenoic and polyenoic fatty acids, the sum of the differences in ω3/ω6 acids and lipids did not exceed 6%. Hence, in total lipids and phospholipids the ω3/ω6 ratio ranged slightly within respective limits of 2.3-2.4 and 3.0-2.8.

The content of vitamin A amounted to 0.05±0.001 mg% in wild haarder eggs, vitamin C averaged 5.15±0.29 mg%, and it was slightly higher as compared with the eggs of caged fish whose values were 0.03± 0.001 and 4.11±0.04 mg%.

Thus, the biochemical composition of eggs obtained from the fish reared in cages and fed with artificial diets did not differ much from the naturally feeding fish, which indicates that adaptive capacities of haarder are high, and it can be reared without losing its nutritional properties. However, the biochemical status of haarder eggs is subject to certain fluctuations, it depends on environmental conditions, including food composition, and these aspects should be also considered in aquaculture practices.