Improved heat stress tolerance for Largemouth Bass fed with natural antioxidant

Largemouth bass (Micropterus salmoides) are one of the most important freshwater aquaculture species in China, facing challenges like high water temperatures that cause significant economic losses. One promising solution is using functional feeds with natural antioxidants. This study by Anne Kristine G. Hansen explored the effects of a natural antioxidant on the growth, survival, and physiological responses of largemouth bass under thermal stress.

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The study was conducted over an 84-day period, from June to September, at the Freshwater Fisheries Research Center in China. Largemouth bass were divided into two groups: one was fed a control diet and the other group, a diet supplemented with a natural antioxidant compound. Each group was housed in five replicate cages, with 40 fish each, and exposed to naturally fluctuating water temperatures that exceeded 32°C for 40 days. Various parameters were measured, including growth performance, survival rate, antioxidant capacity, immune function, and biochemical indicators from blood and liver samples. 

Results 

Growth and Survival

The study found no significant differences in growth performance between the control group and the group fed the antioxidant-supplemented diet. Specific growth rate (SGR), feed conversion ratio (FCR), hepatosomatic index (HSI), and visceral somatic index (VSI) were comparable between the two groups. However, the antioxidant diet significantly improved the survival rate, reducing mortality from 42% in the control group to 31% in the treated group. 

Antioxidant and Biochemical Parameters

Fish fed the antioxidant diet exhibited enhanced antioxidant defenses, as evidenced by increased activities of superoxide dismutase (SOD), glutathione peroxidase (GPx), and catalase (CAT), and higher levels of glutathione (GSH) and total antioxidant capacity (T-AOC). These fish also showed reduced levels of malondialdehyde (MDA), a marker of oxidative stress. Biochemical analyses revealed lower plasma glucose (GLU) and lactate dehydrogenase (LDH) levels, indicating a reduced stress response. 

Immune Function and Stress Markers

The antioxidant-supplemented diet led to significant improvements in immune function and stress markers. Notably, fish on the antioxidant diet had lower alanine aminotransferase (ALT) and aspartate transaminase (AST) levels, enzymes associated with liver damage and stress response. Additionally, total protein (TP) levels were higher, and triglyceride (TG) levels were lower in the treated group, suggesting better metabolic health and energy utilization. 

Water temperature and cummulative mortality. The test additive signifcantly reduced the mortality (P<0.05)

This study demonstrates that dietary supplementation with natural antioxidants can significantly enhance largemouth bass's robustness and survival during thermal stress periods. The improved antioxidant defenses and reduced stress markers observed in the fish suggest that natural antioxidant help mitigate the negative effects of high water temperatures, which is crucial for maintaining healthy and productive aquaculture operations.

Incorporating natural antioxidant compounds into the diets of largemouth bass can be an effective strategy to improve their tolerance to thermal stress. These findings support the potential role of functional feeds in enhancing fish health and resilience, thereby contributing to more sustainable aquaculture practices.