Biochemical composition of zooplankton community grown in freshwater earthen ponds: Nutritional implication in nursery rearing of fish larvae and early juveniles

This study was conducted to obtain a database describing the nutritional value of freshwater mixed zooplankton that are widely used for larval and grow-out rearing of freshwater fish. The macro and micronutrient composition of mixed zooplankton samples collected from 6 fertilized earthen ponds were analysed for protein, lipid, carbohydrate, ash and these ranged from 73-79%, 10.79-14.55%, 3-4.79% and 3.20-10.07%, respectively on a dry matter (DM) basis. Amino acid profile showed the presence of all the ten essential amino acids with low level of methionine. The content of saturated fatty acids (SAFA), mono unsaturated fatty acids (MUFA) and polyunsaturated fatty acids (PUFA) ranged from 64-81%, 7-15% and 6-20% of total fatty acids, respectively. The predominant fatty acids were SAFA (16:0), MUFA (18:1n-9), PUFA viz. linoleic acid (LA 18:2 n-6) and linolenic acid (LNA 18:3 n-3). Among the vitamins, ascorbic acid (15-40.01 μg/gDM) was less than the requirement of fish especially for larvae, vitamin-A (13.61-63.95 μg/g DM) and vitamin-E (218-348μg/g DM) were more than the requirement of fish. Mineral and trace element content showed the presence of P, Ca, Fe, Cu, Zn and Mn. Seasonal variation of all biochemical components was evaluated in the study. Vitamin E had strong co-relation (r1 = 0.72; r2 = 0.88; r3 = 0.83; r4 = 0.86; r5 = 0.36 and r6 = 0.88) with seasonal variation in lipid content of zooplankton of different ponds and varied inversely with that of rising temperature. Enzyme content from the mixed zooplankton of different ponds showed availability of protease (6.21-7.92 μg leucine/ mg protein/h), lipase (25.82-39.1 μg α-naphthol/mg protein/h) and amylase (100-226.1 μg maltose/mg protein/h), which could be used as an exogenous source of digestive enzymes for fish and shellfish during ontogenesis. Absence of l-gulonolactone γ-oxidase activity confirmed the incapability of these zooplankton to synthesize ascorbic acid (AA) de novo. The average dry weight in zooplankton in different ponds was 1.2-4.2 mg/l and different species present in these ponds were Moina (Moina dubia), Daphnia (Daphnia lumholtzi, Daphnia carinata); Cyclops (Mesocyclops hyalimus, Mesocyclops leuckarti); Diaptomus (Heliodiaptomus viddus, Neodiaptomus handeli); Rotifer (Brachionus). These results indicate that the biochemical composition and subsequently the nutritional value of these planktonic organisms are not only genetically determined but also influenced by its maturity stage and type of ingested food. These data may be helpful for reference purpose and for formulated feed preparation accessing the nutritional potentiality of these freshwater zooplankton in the nursery rearing of freshwater fish larvae and early juveniles.