Nutritional evaluation of groundnut oil cake in formulated diets for rohu, Labeo rohita (Hamilton) fingerlings after solid state fermentation with a tannase producing yeast, Pichia kudriavzevii (GU939629) isolated from fish gut

De-oiled groundnut oil cake (GOC) was bio-processed through solid state fermentation (SSF) for 15 days at 34 ± 1 °C by a tannase producing yeast, Pichia kudriavzevii (GU939629) isolated from the gut of a freshwater carp, Cirrhinus cirrhosus. SSF of GOC was effective in significantly (P < 0.05) reducing crude fibre content and antinutritional factors (e.g., tannin, phytic acid and trypsin inhibitor), whereas enhancing crude protein, lipid, ash, total free amino acids and fatty acids. Bio-processing revealed significant increase in the levels of argenine, histidine, isoleusine, lysine, methyonine and threonine in the GOC. Eight isonitrogenous (37.5%) and isocaloric (18.8 kJ g−1) experimental diets were prepared incorporating raw (R1–R4) and fermented (F1–F4) GOC at 20%, 30%, 40% and 50% levels by weight replacing fishmeal and other feed ingredients into a fishmeal-based reference diet (RD) and fed to rohu, Labeo rohita, fingerlings (initial weight 3.24 ± 0.11 g) for 80 days. In general, diets with SSF-processed GOC produced significantly better performance than the raw GOC in terms of growth, feed utilization, nutrient digestibility, carcass composition and digestive enzyme activity. Rohu fingerlings fed the diet F3 containing 40% fermented GOC resulted in best performance in terms of weight gain (final weight 7.08 ± 0.06 g), specific growth rate (% day−1), protein efficiency ratio and apparent net protein utilization. Highest protein (14.93 ± 0.51%) and lipid deposition in the carcass were also recorded in the group of fish reared on diet F3. In comparison to the FM based reference diet, the present study explored the possibility of replacing 45–55% of FM through incorporation of 40–50% (w/w) SSF-processed GOC in the diets for rohu fingerlings.