Document Type : Original Articles
Authors
1
Inland Waters Aquatics Resources Research Center, Iranian Fisheries Sciences Research Institute, Agricultural Research, Education and Extension Organization, Gorgan, Iran.
2
Cotton Research Institute of Iran, Agricultural Research, Education and Extension Organization, Gorgan, Iran.
3
Department of Aquatic Animal Health, Faculty of Veterinary Medicine, University of Tehran, Tehran, Iran.
10.32598/ijvm.20.1.1005643
Abstract
Background: The use of plant-based feeds is increasing in the aquaculture industry. However, these diets have negative effects on fish, which must be addressed. Organic acids (OA) showed benefits in plant-based feed in aquaculture.
Objectives: This project aimed to investigate the effect of adding cottonseed (CS) meal and a mixture of OA to the diet on blood immunity indices, histopathology, and gut microbial population in rainbow trout.
Methods: To this end, 6 treatments consisting of 6 dietary formulations with 3 replications were designed in a 3×2 factorial arrangement. In this design, two levels of CS meal (0% and 15%) and three levels of the organic acid mixture (a mixture of lactic acid, citric acid, and potassium sorbate in equal proportions) at 0%, 0.5%, and 1% were added to the diet. A total of 270 rainbow trout with an Mean±SD weight of 0.14±0.35 g were stored in 18 aquariums containing 40 L of water, with a density of 15 fish per aquarium. The diets mentioned above were provided to the fish for 8 weeks at a daily rate of 3% to 4% of their biomass. After 8 weeks of rearing, blood and liver samples were collected from all treatments.
Results: CS meal and OA had no significant effect on white blood cells, total immunoglobulin levels, or intestinal histology. CS meal did not significantly affect lysozyme, complement, total protein, albumin, or plasma globulin. However, the OA led to a significant increase in these parameters. The addition of CS meal increased lactic acid bacteria (LAB) and Vibrio sp. in the fish’s gut but did not affect the total number of gut bacteria. OA resulted in a decrease in total bacteria and Vibrio abundance while increasing LAB abundance in the gut.
Conclusion: In conclusion, adding 15% CS meal to the diet of rainbow trout does not impact blood immune responses or intestinal tissue structure. However, it increased both beneficial (lactic acid bacteria) and harmful (Vibrio sp.) gut populations. On the other hand, adding OA effectively addresses this issue by increasing LAB populations and decreasing Vibrio sp. population. Furthermore, regardless of the addition of CS meal to the diet, incorporating OA improves innate immune parameters in the blood.
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