Hydrothermically processed Prosopis juliflora (PJ) seed meal as a supplementary diet for Labeo rohita is found to be rich in protein (330 g kg−1) having antinutritional factors in permissible limits and containing essential amino acids adequately except lysine, methionine and cysteine. Ten iso‐nitrogenous and iso‐energetic diets with crude, soaked and autoclaved seed meal at 20%, 35% and 50% replacement of fish meal were tested (D1–D9, respectively). The growth of fish (weight gain, specific growth rate, feed conversion ratio and protein efficiency ratio) fed diet D4 (soaked seed meal at 20% replacement) was higher among the test diets, but lower than reference diet (RD). Diets with 50% seed meal resulted in lowering of growth, carcass composition, digestive enzyme activity and digestibility compared to test diets at 20% and 35% inclusion levels in the respective groups. Hydrothermically processed seed meal improved the growth compared to unprocessed one, though not up to RD level. This could be because of amino acid imbalance and presence of non‐starch polysaccharides in seed meal. Looking to the easy availability and its nutritional quality, processed PJ seed meal can be incorporated in carp diet at lower inclusion level.

The effects of corn steep liquor (CSL), a by-product of corn starch industry, in the fish diet at 25% (D1), 50% (D2) and 75% (D3) replacement of fish meal are investigated on the growth of Labeo rohita (rohu) fingerlings. Formulated feeds were isonitrogenous (39% crude protein) and iso-energetic (15.8 kJ/g). The CSL is found to be rich in protein (43.48%), lactic acid (20.79%) and minerals and is free from fibres, phytic acid and trypsin inhibitors. The sulphur amino acid content of CSL is found to be 2.43%, though it is deficient in lysine (0.73%). With diets D1 and D2, growth performance and feed efficiency in terms of weight gain, specific growth rate (SGR), feed intake, feed conversion ratio (FCR) and protein efficiency ratio (PER) as well as apparent digestibility (APD and ALD) were higher when compared to CD. With diet D3, they were similar to CD. Up to 50% level of CSL in the diets (D1 and D2), the protein and lipid contents of carcass were significantly higher (P \ 0.05) when compared to CD. The digestive enzyme activities are found to be similar in all the diet groups. The findings suggest that in the diet of rohu, fish meal can be replaced up to 75% level with CSL without hampering the growth of the fishes. The CSL appear to be a better plant protein source as partial replacement of fish meal.

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