Evaluation of Azolla pinnata as a Protein Source in the Diet of Silver Barb (Barbonymus gonionotus) During Fry-to-Fingerling Rearing under Hill Conditions of Meghalaya

A 45-day study evaluated Azolla pinnata as a sustainable protein alternative to mustard oil cake in silver barb (Barbonymus gonionotus) fry diets under hill conditions. Conducted at ICAR-Fisheries Research Complex, Meghalaya (950 m altitude), the trial used outdoor concrete tanks (1000 L) from May to June 2023. Seven isonitrogenous diets (30% crude protein) were formulated, replacing mustard oil cake with dried Azolla at 0% (Control), 10%, 20%, 30%, 50%, 80%, and 100%. Fry (initial length: 1.8±0.12 cm; weight: 0.12±0.01 g) were stocked at 200000 ha^-1, with triplicate treatments. Feeding rates were adjusted from 10% to 5% of body weight over time. Water quality remained optimal: temperature (22.8-23.4°C), dissolved oxygen (6.0-6.8 mg L^-1), pH (7.4-7.7), and alkalinity (142.3-156.8 mg L^-1). Growth parameters, feed conversion ratio (FCR), and survival showed no significant differences (P>0.05) up to 50% Azolla inclusion (SGR: 5.28-5.43% day^–1; FCR: 1.80-1.89; survival: 90.5-93.2%). Regression analysis indicated an optimal inclusion level of 47.8% (R²=0.92). Higher inclusion levels (80-100%) reduced growth, survival, and economic efficiency. This research establishes that dried A. pinnata can successfully substitute up to 50% of mustard oil cake in silver barb fry diets while maintaining comparable growth performance, offering aquaculture practitioners in hill regions a sustainable and locally available protein source.