Abstract
This study evaluated the effect of pH on the activity of antioxidant and immune enzymes in the sea cucumber Isostichopus badionotus exposed to different temperatures. The organisms (530 ±110 g) were exposed to 16, 20, 24, 28, 30, 34 and 36°C for 6 h to evaluate thermal limits at two water pH values (treatment = 7.70; control = 8.17). For the thermal tolerance experiment, the organisms were exposed to sublethal temperature of 34°C for 3, 6, 12, 24, and 48 h. I. badionotus showed signs of thermal stress by synthesizing heat shock protein 70 (hsp70) at the cold (16°C) and warm thermal limits (34°C). The glutathione peroxidase (GPx) showed a negative correlation with superoxide dismutase (SOD) activity in modulating the effect of oxidative stress at different temperature levels. Specifically, GPx activity was maximal at the extremes of the cold and warm temperatures (16, 20, and 36°C) tested, while contrarily, the SOD activity increased significantly in the narrow range of temperature between 28 and 30°C, as a part of a reaction to offset oxidative damage. The effect of pH on the expression of hsp70 was not significant, whereas the antioxidant enzymes activity was stimulated at pH 7.70. Mucosal immunity, evidenced by the activation of the phenoloxidase (PO) system, increased above the basal level at pH 7.70 and at 28, 30, and 34°C. Independent of pH, the temperature of 34°C was identified as the 12 h-sublethal upper limit for I. badionotus.
Highlights
The sea cucumber Isostichopus badionotus (Echinodermata: Holothuroidea) is a large epibenthic holothuroid distributed along the Western Atlantic coast from South Carolina to Brazil, including the Antilles, and the Gulf of Guinea in the Eastern Atlantic [1, 2]
The results of the present study clearly identify the upper lethal thermal limits of the tropical sea cucumber I. badionotus
Hsp expression, which is considered as a bioindicator of thermal stress in sea cucumbers [26], significantly increased at 30–34 ̊C, confirming that this temperature range induces thermal stress in I. badionotus (Fig 1)
Summary
The sea cucumber Isostichopus badionotus (Echinodermata: Holothuroidea) is a large epibenthic holothuroid distributed along the Western Atlantic coast from South Carolina to Brazil, including the Antilles, and the Gulf of Guinea in the Eastern Atlantic [1, 2]. In the last ten years, I. badionotus has been subject to intense fishing in the southern Gulf of Mexico, the Caribbean islands, and the Central American countries due to a high demand in Asian. Many efforts have been made to stabilize its aquaculture such as contributing knowledge of its vulnerability to different environmental conditions. In their natural environment, sea cucumbers from southern Gulf of Mexico are exposed to seasonality, which often results in fluctuations in water pH that ranges between 7.3 and 8.6 [3, 4]. During the north wind season (October to January), the water temperature decreases from a maximum of 32 ̊C to an average of 21 ̊C [5]
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