Nutritional and Immunological Studies on Fermented Soybean Products in Diets for Marine Fishes

Abstract

Many studies recently have been being conducted to minimize the feed costs and to enhance immune responses and diseases resistances of farmed fish. In line of the current direction, this study was conducted to investigate the effects of fermented soybean and cottonseed meal with different bacteria and fungi on growth performance and non-specific immune response of marine fish species, including parrot fish, Oplegnathus fasciatus and olive flounder, Paralichthys olivaceus. To pursue the purposes of the study, four feeding experiments were conducted with different Korean traditional fermented soybean products including Cheongkukjang (CKJ-Chapter I), Meju (MEJU-Chapter II) and fermented soybean and cottonseed meal with MEJU microorganisms (Chapter III and IV). In the first two feeding experiments, effects of dietary CKJ and MEJU on growth performance, phosphorus utilization and immune response in juveniles of parrot fish and olive flounder were examined. Higher liver superoxide dismutase (SOD) activity and phosphorus retention were observed in both parrot fish and olive flounder fed the diets contained either 25% CKJ or 6% MEJU, compared to those of fish fed the fish meal based diets. The diets supplemented with 25% CKJ or 6% MEJU did not affect the growth performance and survival of the fishes. The findings from Chapter I and II suggested that increase of liver SOD activity and phosphorus retention might be contributed by presence of some enzymes and higher antioxidant activities produced by micro-flora in both CKJ and MEJU. Based on the findings in the previous two feeding experiments, a six week feeding experiment was conducted to investigate the effects of fermented soybean meal by four probiotics including Aspergillus oryzae (SBM-AO), Sacchromyces cerevisiae (SBM-SC), Pediococcus pentosaceus (SBM-PP), and Bacillus subtilis (SBM-BS) on immune response of juvenile parrot fish. At the end of the feeding trial, fish fed the diet contained SBM-AO produced higher liver catalase (CAT) and antioxidant activities than did the fish fed the SBM diet. The findings suggest that Aspergillus oryzae was superior to the other examined probiotics. Fermented SBM with A. oryzae might enhance immune response of parrot fish. A. oryzae could be a suitable fermentation microorganism for other plant protein sources such as cottonseed meal. The lower growth performance in the fish fed the fermented soybean meal diets might be associate with deficiency of some essential amino acids and antinutitional factors produced in fermentation process. Finally, a six week feeding experiment was conducted to investigate the effects of fermented cottonseed and soybean meal (CS) with A. oryzae on growth performance, hematological parameters of parrot fish. Fermentation process produced higher antioxidant activities in CS. Lower plasma cholesterol and trygliceride levels were found in fish fed the diets containing fermented cottonseed and soybean meal (F-CS), compared to fish fed the fish meal and CS containing diets. However, fish fed F-CS and CS40 diets grew slower compared to fish fed the control and the other diets. The findings indicate that CS could replace up to 30% dietary fish meal for parrot fish without adverse effects on growth performance. Deficiency of some essential amino acids and antinutitional factors produced in fermentation process might have affected growth and utilization of nutrients in the fish. In conclusion, dietary inclusion level of 25% CKJ or 6% MEJU could enhance innate immune response and increase phosphorus utilization of parrot fish and olive flounder. Fermented soybean meal with Aspergillus oryzae could increase immune response in juvenile parrot fish. For effective use of fermented cottonseed and soybean meal as immune-stimulants in aquaculture, further studies are necessary to optimize the fermentation condition and to address the growth impairment due to the loss of amino acids and lower protein solubility during fermentation process.