Hypoxic conditions induce Hsp70 production in blood, brain and head kidney of juvenile Nile tilapia Oreochromis niloticus (L.)

Abstract

The objective of this study was to evaluate the effects of hypoxia, elevated ammonia levels and crowding on the physiological and cellular stress responses of juvenile Nile tilapia Oreochromis niloticus (L.). The experiment was designed to be representative of prevalent harvest practices often encountered with this species. The levels of innate and inducible heat shock protein 70 (Hsp70) were measured in blood (packed cells), brain, liver, muscle and head kidney tissues of tilapia exposed to hypoxic stress (∼4.9–0.3 mg l −1 dissolved oxygen), reduced water levels which tripled the fish/unit of water and an increase in ammonia levels from below detection limits on Day 1 to less than 0.5 mg l −1 at the end of 48 h. A highly significant increase in Hsp70 (*** P<0.0001) was detected in packed blood cells, brain, and muscle tissues in test fish compared to control treatments, but no differences were observed among treatments in liver (* P=0.93) and head kidney (* P=0.24) tissues. A highly significant increase (*** P<0.0001) was detected in serum glucose levels due to hypoxia treatments, and a statistically significant difference was detected among serum cortisol levels (* P<0.05). The Hsp70 results reported here suggest that a physiological response as well as an inducible cellular stress response occurs in this species subjected to these stressful conditions, and that the cellular responses are tissue-specific and have not been observed in other teleosts species.