Introduction
Feed is necessary in aquaculture, just like in animal husbandry, to guarantee good production, particularly in intensive culture systems that demand a lot of input (Boyd, 2020). Since feed makes up over 50% of the entire production expenses in the aquaculture business, feed is a crucial component (Mzengereza et al., 2014). The costliest feed ingredient in aquafeeds is the source of protein (Lim et al., 2023). Fishmeal is considered the gold standard protein due to its balanced amino acid content, which is perfect for the healthy growth and development of fish (Perez-Velazquez et al., 2019). Fish by-products and wild-caught fish are used to make fish-meal, an industrial product (Wan, 2015). Fishmeal is a major source of aquafeed worldwide. However, the rising demand for fish and fish products has caused its price to continuously rise, greatly affecting the market price (Jannathulla et al., 2019). To cut feed costs, several plant-based proteins are now utilized in place of fish-meal, either totally or partially (Jannathulla et al., 2019). The main objective of using plant-based proteins is to offer fish-meal as a more affordable substitute. Finding a less expensive option isn’t the only factor, though (Gutasi, 2021). Moreover, the production of these plant-based proteins needs to be sustainable without affecting the health and growth of fish (Magbanua and Ragaza, 2024). Consequently, the aim of this study was to evaluate the effects of soybean husk, cowpea husk, and palm kernel meal as protein sources on growth performance, feed utilization, intestinal histology, and health of catfish using full blood count and liver function test as indicators.
Materials and Methods
Formulation of the experimental diets and feeding
Table 1 shows the experimental diets used for this study. In formulating the diets, substantial amount of fish meal was progressively replaced with soybean husk (SBH), cowpea husk (CPH) and palm kernel meal (PKM) until equal amounts of protein (approximately 35%) were obtained. Following procedures previously described by Ayisi et al. (2017), the formulated diets were prepared. C. gariepinus were fed to apparent satiation, three times daily at 8:00 am, 12 noon and 4:00 pm for ten weeks.
2.2. Experimental conditions and design
The experiment was carried out in concrete tanks with dimensions of 1.5 m x 1.5m x 1.2 m (length, breadth and depth). Five hundred healthy C. gariepinus with initial weight of approximately 2.5 g were purchased from a commercial farm and transported to the rearing facility. Prior to the onset of the trial, fish were acclimatized to the rearing conditions for 2 weeks and fed on commercial diet with protein content of 32%. At the onset of the trial, the fish were distributed into four groups with duplicates and fed their respective diets. Each tank was stocked with fifty fish.
2.3 Measurements of the biological indices
Feed utilization and growth performance were measured following formulas previously used by Mutalib et al. (2023).
2.4 Blood biochemical analysis
After 10 weeks of feeding trial, blood from experimental fish were sampled and blood biochemical analysis performed as previously described by Abarike et al. (2018).
2.5 Proximate composition
Samples from whole body fish and experimental diets were sent to the laboratory for protein, lipid, moisture, and ash analyses. The AOAC (2003) standard methods, as reported by Ayisi et al. (2021), were employed to analyze the aforementioned parameters.
2.6 Histological examination
Six fish per group had sections of their intestines removed, which were then quickly preserved in a Bouin solution for histological examinations. Samples of tissue were promptly preserved in a Bouin solution. After that, fixed samples were subjected to a series of alcohol solutions with increasing grades (70–100 percent) to dehydrate them. Following the dehydration procedure, tissues underwent xylene deparaffinization, paraffin embedding, 5 μm sectioning, and Hematoxylin and Eosin (H&E) staining (Ismail, et al. 2020). A Leica light microscope was used to examine the slides, and an eyepiece camera was used to capture the images. ImageJ version 1.54 was used to determine the target cells in each section.s
2.7 Statistical analysis
The gathered data was statistically analyzed using Graph Pad Prism (V.5.03). The data is presented in tables using the standard error of the mean (SEM), which is represented as the mean ±. To compare treatment means, One-way Analysis of Variance and Tukey’s multiple tests were applied to all the data. Differences are considered significant for all data at the 0.05 probability level (P<0.05). Pearson’s correlation was conducted to ascertain the relationship between selected parameters. Results of correlation analysis is presented in figures.
Results
The results indicated that inclusion of these alternative protein sources had significant effects on growth performance and feed utilization compared to FM diet. The weight gain recorded in this study was as follows: SBH (119.5±68.02) > CPH (113.2±53.14) > FM (104.3±56.82) > PKM (86.73±31.51). Feed conversion ratio ranged from 1.25±0.57 (SBH) to 1.52±0.56 (PKM). C. gariepinus fed the diet PKM had the lowest protein efficiency ratio (2.09±0.76), followed by those fed the FM (2.57±1.40) and the CPH diet (2.74±1.28). To a larger extent, the dietary protein sources significantly influenced serum hematology parameters. C. gariepinus fed the FM diet had the highest white blood cells count (133.0±2.51), which was significantly higher than all other groups (p < 0.0001). The range of red blood cell values observed in this study was 2.08±0.13 to 2.62±0.13. Histological examination indicated modifications in intestinal morphology, suggesting possible metabolic adjustments to the experimental diets. Fish fed the FM had the highest villus height (441.2±22.6), followed by SBH (398.3±7.51), PKM (279.2±15.65), and CPH (142.3±10.84). Villus width and muscular thickness also followed this pattern, with fish fed the FM diet having the largest villus width (153.7±9.06), significantly greater than all other groups (p<0.0001). Overall, incorporating CPH, and SBH into catfish diets appears to be a viable replacement for conventional fishmeal-based diets; however, further studies are required to determine optimal inclusion levels for achieving maximum growth and well-being.
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