Dietary essentiality of ascorbic acid in rohu larvae: Quantification with ascorbic acid enriched zooplankton

Carp larvae, like any other fish larvae dependon natural food during first few days of theirlife. In nursery conditions, high mortality andslow larval growth are of common occurrence;sub-optimal nutrition might be a possiblereason for such consequences. To improve thesituation the effect of feeding ascorbicacid-enriched live food on survival, growth,tissue biochemical composition includingascorbate level was evaluated in first feeding(3 days old) larvae (av. wt. 2.2 mg) of therohu carp, Labeo rohita (Ham.) for aperiod of 15 days (temp. 28.6 ± 1 °C)under natural photoperiod. The larvae (stockingdensity 10 l^–1) were offered enriched andnon-enriched zooplankton ad libitumfollowing a rigid schedule with four feedingregimes, each having 3 replicates. In treatmentT₁, non-enriched zooplankton (Moina,Daphnia, Cyclops, Diaptomus) and in T₂,T₃, T₄ ascorbic acid enriched (12 henrichment) zooplankton @10%, 20% and 30%ascorbyl palmitate (AP) inclusion in diet ofzooplankton] were offered. Highest survival(90%) and growth (9563% live weight gain)could be seen in T₃ group and the lowestin T₁ (62% survival and 805% live weightgain), thus confirming the dietary essentialityof ascorbic acid for rohu larvae. Therequirement has been shown to be 1409 µg/gdry diet. Whole body tissue analyses for crudeprotein, total lipid and RNA: DNA ratiofollowed the same trend as that of growthresponse and percent survival. Significantpositive correlation (r = 0.949 and 0.861) couldbe found with muscle RNA/DNA ratio and muscleRNA content with specific growth rate indifferent treatments. Significant differencewas found in tissue ascorbate levels betweenenriched plankton fed groups, being highest in T₃. Such live foodmediated vitamin transfer might be an effectivemeans to provide higher plane of nutrition forhigh survival and rapid growth for rohu larva.