Yeast fermented Azolla pinnata meal in diets of silver barb Barbonymus gonionotus: Growth performance, protein digestibility and muscle composition under mid-hill conditions of Meghalaya

Abstract

A 45-day feeding trial in 1000-litre cemented tanks under mid-hill conditions of Meghalaya (mean water temperature 20.8±0.9⁰C) evaluated the effect of graded replacement of unfermented Azolla pinnata meal (UAM) with yeast fermented Azolla pinnata meal (FAM) on growth performance, survival, condition factor, apparent protein digestibility and muscle proximate composition of juvenile silver barb (Barbonymus gonionotus). Five isonitrogenous diets with fish meal (23%), mustard oil cake (25%) and rice bran (30%) fixed identically were formulated with 0% (T1), 25% (T2), 50% (T3), 75% (T4) and 100% (T5) FAM replacement of the 20% UAM component. Fish (initial weight 12.21±1.31 g, 20/ tank, triplicate) were sampled on days 0, 7, 15, 30 and 45. Specific growth rate improved progressively from T1 (0.84±0.07 % day⁻¹) to T4 (1.16 ±0.07 % day⁻¹), feed conversion ratio from 2.61 ± 0.21 to 2.08±0.14, and apparent protein digestibility from 72.14±1.84% to 83.47±1.62%, with T4 and T5 statistically comparable in all parameters (P>0.05). Survival, condition factor and muscle crude protein followed the same trend. Results suggest yeast fermentation reduces antinutritional factors and improves protein digestibility of azolla, with 75% FAM replacement offering a practical optimum for silver barb under hill aquaculture conditions.