Utilization of fermented animal by-product blend as fishmeal replacer in the diet of Labeo rohita

• Up to 75% replacement of fishmeal by fermented blend of fish offal and slaughter house blood in the feed there was no negative impact on growth of Labeo rohita.
• Protein utilization by L. rohita was found maximum at 25% replacement level.
• Multi-objective optimization programming indicated 21.11% replacement of fishmeal by the fermented blend as ideal for optimum growth.

Experiments were carried out to evaluate efficiency of Labeo rohita to utilize fermented animal protein blend containing slaughter house blood (SHB) and fish offal (FO) as dietary fishmeal (FM) replacer. Five isoproteic (30%), isolipidic (8%) and isoenergitic (15.00 kJ g−1) feed were prepared by replacing 0 (T1), 25 (T2), 50 (T3), 75 (T4) and 100% (T5) FM protein with the fermented blend and fingerlings of L. rohita (mean weight 2.07 g) were fed each of these feed in triplicate groups. The results showed that apparent digestibility coefficient (ADC) of protein significantly increased in T3–T5, while ADC of lipid and total amino acid absorption rate increased in T2–T5 as compared to control (T1). Among the essential amino acids (EAA), arginine exhibited maximum absorption followed by histidine, phenylalanine, valine and lysine while aspartic acid showed a high absorption among the non-essential amino acids (NAA). Fish fed up to 75% of replacement level (T4) did not show any significant difference (P < 0.05) in weight gain (WG), specific growth rate (SGR), feed conversion ratio (FCR), protein efficiency ratio (PER) and apparent net protein utilization (ANPU) between the dietary groups (T1–T4). But FCR was increased and other growth parameters were significantly reduced in 100% replacement group (T5), while body muscle protein was significantly reduced in both T4 and T5. Deposition of EAA (except histidine and methionine) in T4 and NAA (except cystine) in both T4 and T5 in the muscle of fish were also significantly reduced as compared to control (T1). Multi-objective optimization programming technique was used to determine FM replacement level that optimized all the growth parameters (WG, SGR, FCR and PER) simultaneously. By using Global Criterion method, it was obtained that 21.11% replacement of FM by the fermented blend was ideal for optimum growth of L. rohita.