Growth and physiological conditions of fish fed diets with fish meal replaced with ESBM appeared acceptable but condition of pompano liver was affected with increasing incidence of granulation and inflammation
By Romi Novriadi and D. Allen Davis
Fish meal (FM) is often considered the preferred protein source for aquafeeds because of its high level of essential amino acids and other essential nutrients. To substantially decrease dietary level of fish meal in aquafeeds, plant-protein sources appear to be the most sustainable ingredient. However, deficiency in some amino acids and the presence of anti-nutrients, such as proteinase inhibitors, phytic acid, saponins and anti-vitamins, limit the use of these ingredients which may have detrimental effects on the digestive process and growth of fish.
Studies conducted with Florida pompano Trachinotus carolinus indicated that the combination of solvent-extracted soymeal with soy protein concentrate (SPC) were able to reduce the fish meal inclusion rates from 30 to 15% without deleterious effect on growth performance (Quintero et al., 2012). Blending conventional soymeal with advanced soy products is likely to be a viable strategy to improve the nutritional value of plant-based diet. However, continued reduction in fish meal levels below 15% will likely reduce the growth performance of this species.
Novel products, such as enzyme-treated soybean meal (ESBM) provide an opportunity to enhance the nutritional quality of plantbased diets for pompano. In the present study we analysed the effect of partial and complete replacement of fish meal with various inclusion levels of ESBM on growth performance, proximate composition of the whole body, amino acid profile, serum and enzyme activities, and histomorphological condition of liver and distal intestine of Florida pompano.
Two trials were conducted to evaluate the efficacy of ESBM to replace the use of fish meal in practical diets for Florida pompano. The reference diet in trial 1 utilised 150g/kg of fish meal, 466.0g/ kg defatted soymeal and 80g/kg corn protein concentrate (CPC). Three experimental diets were formulated to include increasing levels of ESBM to reduce fish meal to 120, 90 and 60g/kg (labelled as 12, 9 and 6% FM, Table 1). Diets in trial 2 were formulated based on the results of trial 1. Four experimental diets were produced to include increasing levels (30, 90, 120 and 150g/kg) of ESBM to partially and completely replace fish meal in the diet (Table 1).
Both growth trials were carried out at the Claude Peteet Mariculture Center (CPMC), Gulf Shores, AL, USA. At the start of the trials, 20 fish with average initial weight of 13.05 ± 0.34g for the first trial and 18.45 ± 0.49g for the second trial were stocked into each tank. Each trial consisted of four treatments each with three replicates in a completely randomized design. Fish from all trials were maintained under natural photoperiod for 8-weeks. During the trials, fish were fed 4x/day on a percent body weight basis. Fish were bulk-weighed every other week to monitor growth and adjust feeding rations. During sampling, fish were dipped in chloroquine phosphate (MP Biomedicals, Solon, USA) as a bactericide at 60mg/L followed with a freshwater dip for approximately 1 minute to reduce possibilities of parasitic infection. During both growth trials, water quality was within the acceptable range for Florida pompano.
At the end of the growth trials, four fish from each tank were randomly sampled and stored at -80℃ for body composition analysis. Blood samples were taken from the caudal vein and collected using anticoagulant-free centrifuge tubes. Serum was obtained by centrifugation of blood at 3,000rpm for 10 min and stored at -80℃ pending analysis. Serum samples were analysed for total protein, albumin, activities of alkaline phosphatase (ALP), alanine aminotransferase (ALT), aspartate aminotransferase (AST), glucose, cholesterol and bile acid concentrations.
Histological analysis was only carried out in trial 1 and samples were randomly collected after an overnight fast with three fish/ treatment tank. Fish were individually dissected to collect the liver and distal intestine. The following parameters were evaluated for distal intestine analysis: the number of goblet cells (GC), level of cellular infiltration (CI) and thickness of the lamina propria within the intestinal folds (WLP). Liver evaluation focused on the presence of hepatocyte vacuolisation, change in nucleus and granulation. Histomorphological images were acquired using a microscope (Olympus BX41, Olympus Optical Co., Ltd., Japan).
For trial 1, survival was over 90% and there were no significant differences in terms of feed intake. However, fish fed the lowest inclusion level of fish meal (6% FM) had a significantly lower final weight, weight gain and thermal growth coefficient. In addition, fish fed the 6% FM diet had the highest feed conversion ratio (FCR, Table 2). For trial 2, there were no significant differences for the above parameters. However, fish fed with completely free-fish meal diet had the lowest final weight compared to other dietary treatment (Table 2). There was reduced growth performance when 15% inclusion level of fish meal was further replaced with soy protein.
For the body composition analysis, there were no significant effects of fish meal replacement on crude protein, fat content, crude fibre, dry matter, moisture and ash content for both trials. No significant effects were observed on the level of total protein in the serum, albumin, glucose, bile acids, ALP, ALT and AST activities. For histological analysis, linear regression modelling suggested severe conditions of pompano liver as indicated by the increasing incidence of granulation and inflammation when fish meal was further replaced by ESBM. A similar condition was also observed in the distal intestine of pompano where the level of cellular infiltration into lamia propria was higher in fish fed with lower level of fish meal. Based on the microscopic observations, there is a tendency toward severe condition as fish meal was further replaced by ESBM (Figure 1 and 2).
An integrated evaluation of novel ingredients by means of growth trial, proximate and amino acid composition of the whole body, serum and enzyme activities in the blood of fish together with microscopical methods for liver and distal intestine tissue analysis provides a comprehensive and reliable assessment of its nutritional effect. In this study, ESBM can be used to reduce the dietary fish meal from 15 to 9g/kg in the development of practical diets for pompano containing 466g/kg of conventional soymeal and together -80g/kg CPC. However, further studies are required to investigate the inclusion effect of ESBM to replace dietary fish meal for a long-term growth duration beyond the current growth trial.
(Extracted from: Novriadi, R., Salze, G., Abebe, A., Hanson, T., & Davis, D. A. (2019). Partial or total replacement of fish meal in the diets of Florida pompano Trachinotus carolinus. Aquaculture Research, 50(5), 1527-1538