Digestibility and water quality investigations on the processed peanut (Arachis hypogaea) meal fed barramundi (Lates calcarifer) at various inclusion levels

Abstract

The present study compared the nutrient compositions of peanut seed (Arachis hypogaea) subjected to three processing techniques; mechanical pressing, fermentation and germination. The study also evaluated the effect of inclusion level (0%, 15 %, 30 % and 60 %) on nutrient digestibility of these meals by juvenile barramundi (Lates calcarifer) and the subsequent discharge of nutrients to the rearing water. A diet containing no peanut meal served as a reference diet. Barramundi of average weight of 31.2 ± 1.2 g were fed on 10 test diets for 4 weeks. Germination processing significantly (p < 0.05) lowered the carbohydrate and hydrolysed fat contents of peanut meal and its protein level. Fermentation and germination significantly affected the protein quality of peanut meal producing a greater proportion of short peptides (<35 kDa) than achieved by mechanical pressing. Fermented peanut meal at any inclusion level resulted in significantly increased ADC of protein, while 60 % inclusion of mechanically pressed and germinated PM reduced the diet ADC of protein. Ionic phosphate (PO4−), chemical oxygen demand (COD) and total suspended solids (TSS) of rearing water of holding barramundi fed peanut meal-based diets were not different to the reference diet measured two, four and six days after water circulation of tanks was stopped. However, after six days, NH4+ decreased in tanks of barramundi fed fermented peanut meal diet while it increased in tanks fed mechanically pressed peanut meal and of those 60 % germinated peanut meal. Overall, it can be concluded that fermentation processing of peanut meal improves its protein digestibility, increases the production of short chain peptides and reduces the concentration of NH4+ entering holding water compared to diet using germinated or mechanically pressed peanut meal.