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Abstract
Simple SummaryThe head kidney was primary organ that accumulated methylmercury in hybrid grouper. Muscle tissue had lower methylmercury content than the head kidney and liver. Nonspecific immune responses and bioaccumulation of methylmercury were linked to hybrid grouper health.Mercury (Hg) is a dangerous heavy metal that can accumulate in fish and is harmful when consumed by humans. This study investigated the bioaccumulation of mercury in the form of methylmercury (MeHg) and evaluated nonspecific immune responses such as phagocytic activity and superoxide anion (O2−) production in hybrid grouper (Epinephelus fuscoguttatus × E. lanceolatus). The hybrid grouper leukocytes were incubated with methylmercury chloride (CH3HgCl) at concentrations of 10–10,000 µg/L to determine cell viability, phagocytic activity, and O2− production in vitro. Subsequently, the grouper were exposed daily to CH3HgCl mixed in the experimental diets at concentrations of 0, 1, 5, and 10 mg/kg for 28 days. The bioaccumulation of MeHg in the liver, head kidney, and muscle tissue was measured, and the phagocytic activity and O2− production were evaluated. In vitro results indicated that cell viability was significantly lower than that of the control group at concentrations > 500 µg/L. The phagocytic rate and O2− production at concentrations ˃ 500 and ˃ 200 µg/L, respectively, were significantly lower than those of the control group. The dietary exposure demonstrated that MeHg accumulated more substantially in the liver and head kidney compared with the muscle tissue in the treatment groups. Moreover, the cumulative concentration significantly increased with higher concentrations and more days of exposure. The phagocytic rate and O2− production in the treatment groups were significantly lower than those in the control group from days 2 and 1, respectively. In conclusion, hybrid grouper accumulated significant MeHg in the liver and head kidney compared with the muscle tissue, and higher concentrations and more exposure days resulted in decreased cell viability, phagocytic activity, and O2− production.
Highlights
Grouper is an important aquaculture species cultivated in Taiwan
Cultured species are primarily tiger grouper (Epinephelus fuscoguttatus) and giant grouper (E. lanceolatus), which are widely distributed in the Indo-Pacific region [2]
This study demonstrated that MeHg exposure can reduce the phagocytic rate, phagocytic index, and O2− production rate in head kidney leukocytes of the hybrid grouper
Summary
Grouper is an important aquaculture species cultivated in Taiwan. As the world’s second largest grouper producer, Taiwan’s production of approximately 234 tons accounted for 10% of the world’s total grouper production in 2019 [1]. Cultured species are primarily tiger grouper (Epinephelus fuscoguttatus) and giant grouper (E. lanceolatus), which are widely distributed in the Indo-Pacific region [2]. Tiger grouper is a popular cultured marine species in Asia due to its rapid growth rate, and giant grouper, which can reach a maximum weight of 400 kg, is the largest grouper species [3]. A crossbreed of these two species is the hybrid giant tiger grouper, which became popular due to its high survival rate, feeding performance, rapid growth rate, and tolerance of a wide range of rearing parameters [4,5]. Grouper aquaculture is mostly conducted in offshore cages; marine culture, which first developed in the 1990s for cobia (Rachycentron canadum), is a current trend in raising giant grouper [6]. Marine environmental pollution from heavy metals has attracted global attention because such pollution harms fish [7]
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