Four commercial solvent‐extracted oilseed meals/cakes, viz. soybean meal (SBM), groundnut oil cake (GNC), rapeseed meal (RSM) and sunflower oil cake (SFC), were fermented with fungus Aspergillus niger, and its effect on apparent digestibility coefficient (ADC) was studied in Penaeus vannamei. Reference diet and eight experimental diets containing 700 g/kg reference diet and 300 g/kg test ingredient with 5 g/kg chromic oxide were formulated. Each diet was randomly allotted to three tanks containing ten shrimps. Shrimps were adapted to the experimental diets for a week, and faeces were collected using Falcon tube from second week onwards. The ADC of all the ingredients significantly (p < .05) increased with fermentation and the increase being higher in SBM (78.46%–91.71%) for dry matter and in SFC (71.51%–87.02%) for protein. Analysis of variance showed that the ADC of both dry matter and protein significantly (p < .05) differed in treatments (p = <.001) and ingredients (p = <.001). The average ADC of ingredients was ranked as SBM > GNC > RSM > SFC. The most digestible essential amino acid (EAA) in fermented ingredients was methionine in SBM, arginine in GNC, valine in RSM and histidine in SFC. A better improvement in amino acid digestibility was observed in fermented SFC. Results indicated that P. vannamei efficiently digests fermented ingredients compared to unfermented ones.

The incorporation of plant protein sources in shrimp feed is limited due to unbalanced amino acids and higher anti-nutrients. In the present study, soybean meal (SBM), groundnut oil cake (GNC), rapeseed meal (RSM), sunflower oil cake (SFC) and guar meal (GRM) were subjected to natural, bacterial, fungal and yeast fermentation methods. The essential amino acid contents were increased by 4-28% in SBM, 7-26% in GNC, 3-27% in RSM, 8-18% in SFC and 4-14% in GRM. The increase was better for lysine with fungal fermentation (2.31-4.01%). The improvement in other limiting amino acids viz., methionine and tryptophan also showed positive response to fermentation. The analytical results showed improved essential amino acid index (EAAI) in the fermented ingredients and the increase was better with RSM (0.82 to 0.92) using Aspergillus niger. Fiber fractions were reduced (p<0.05) in fungal and yeast treated samples but not due to natural or bacterial fermentation. The reduction of cellulose and hemicellulose was not only influenced by the inoculum but also on the ingredient used. The reduction of anti-nutrients (p<0.05) such as trypsin inhibitor, phytic acid, saponin, tannin, glucosinolate and guar gum were found to be lower in natural fermentation than other methods. The results indicated that fungal fermentation is more suitable for improving the nutritional quality of plant protein sources and this data will pave way for higher fishmeal replacement in shrimp feed formulations.

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Using the 70:30 replacement method and chromium as an inert marker, the digestibility of four fermented oilseed meals/cakes (soybean meal (FSBM), groundnut oil cake (FGNC), rapeseed meal (FRSM), and sunflower oil cake (FSFC)) were determined in Penaeus monodon and Penaeus indicus. Apparent dry matter digestibility (ADMD) of fermented ingredients was ranked as FSBM > FGNC > FRSM > FSFC. The critical variations in apparent protein digestibility (APD) in P. monodon (0.816%) and P. indicus (0.608%) were lower than the ADMD. Appaprent amino acid digestibility (AAD) was >90% in FSBM for both the species and was lower for other ingredients. Protein had a higher digestibility than total amino acids and was in the range of 0.69%–2.71% in P. monodon and 0.32%–2.75% in P. indicus. A correlation between the ADC of total amino acids and protein was found to be r = 0.8229 in P. indicus and r = 0.7447 in P. monodon. Data were further subjected to two way analysis of variance for assessing the digestibility variations between the species. It was observed that P. indicus had higher values of ADMD than P. monodon in FSBM (2.97%) and FRSM (1.22%) and the reverse was true in FGNC and FSFC. The APD was high in P. indicus for FSBM, FGNC and FRSM but not for FSFC. However, significant variations could be noticed in AAD between the species.