Extreme water temperatures related to global climate change represent a significant challenge in terms of fish welfare and aquaculture productivity. Understanding the effect of more frequent and extended extreme temperature events on physiological responses, growth performance and other production-relevant parameters of major aquaculture species are essential for developing suitable mitigation methods and assuring future production. European seabass, Dicentrarchus labrax , a euryhaline marine aquaculture species is widely distributed throughout the Mediterranean region . This fish grows best at a temperature range of 22 o C to 24 oC. This fish is reportedly sensitive to temperatures below 11 oC and over 25 o C, which leads to impairments of growth, physiology and high mortality rates. In the Mediterranean region, maximum water temperature in ponds exceeds 33-34 o C during late spring to August and decreases to 5-6 °C winter .
The present study evaluated the extreme ambient temperature effect on growth performance, physiological, biochemical and molecular responses of juvenile European seabass, Dicentrarchus labrax . Fish exposed to 8 °C and 32 °C for 30 days exhibited significantly lower final weight, weight gain, specific growth rate, survival rate, and temperature growth coefficient (p<0.05), compared to 16 °C and 24 °C. Hepatosomatic index (HSI), viscera somatic index (VSI), intestine somatic index (ISI) and spleen somatic index (SSI) were significantly (p<0.05) lower in fish at 8 o C and 32 oC at day 30. Plasma [Na+] and [Cl- ] ion concentrations were significantly lower (p<0.05) in fish reared at 8 o C at day 10, 20 and 30. Plasma triglycerides, lactate, cortisol were significantly (p<0.05) increased, while plasma glucose, protein and liver energy storage showed the inverse trend in 8 o C and 32 o C reared fish at day 10, 20 and 30. Heat shock proteins (hsp70) gene was significantly (p<0.05) upregulated in the dorsal muscle and kidney tissue of fish reared at 8 o C and 32 oC at day 10, 20 and 30. Whereas Interleukin 1β (IL-1β) gene exhibited a similar, but less regular expression with upregulation at day 10 across all four temperature treatments. Insulin growth factor 1 (Igf1) relative expression was decreased significantly in fish reared in 8 o C and 32 o C than in 16 o C and 24 o C at day 10, 20 and 30.
European seabass exhibits significant physiological, biochemical and gene expression alterations and marked performance reduction during extreme temperatures of 8 o C and 32 oC. None of the repeatedly measured parameters in the current study indicated a capacity for compensation by physiological adaptation over periods of 10, 20 or 30 days.