Transcriptional Response of Delta-9-Desaturase Gene to Acute and Chronic Cold Stress in Nile Tilapia, Oreochromis niloticus

Tilapia is a warmwater fish and a popular choice for aquaculture. However, cold sensitivity of tilapia is a constraint to expansion of tilapia culture into the colder regions of the world. Tilapia generally require a thermal environment of 25-30 C. Acclimation to cold requires changes in gene expression such as delta 9 desaturase (delta 9D) which is widely expressed in many poikilothermic animals in the process of cold acclimation. A major function of delta 9D is to desaturate membrane lipids in order to sustain membrane fluidity during cold. In this article we examined the effect of acute and chronic cold stress (12-14 C) on the expression of the delta 9D gene in muscle, gill, heart, and liver of growing Oreochromis niloticus. Despite the relatively cold temperatures, none of the fish were killed by the cold stress. Results indicate that there was no significant change in expression of delta 9D during acute cold stress. The expression of delta 9D in liver and heart tissues was not chronically affected by cold (7 d); however, delta 9D expression of muscle and gill tissue was increased in response to chronic cold stress. Muscle was the most responsive tissue demonstrating greater than 16-fold increase following 7 d of cold exposure. Unlike many other cold tolerant teleost fish, tilapia liver delta 9D transcription was not affected by acclimation to chronic cold stress. It is possible that upregulation of expression of delta 9D in muscle and gill tissue reflects the requirement of these tissues in maintenance of a higher metabolism associated with the need to sustain oxygen consumption, mobility, and heat generation. In contrast, reduced expression of delta 9D in liver may reflect lower overall metabolic rate during cold.