Effects of water temperature on growth, health and digestive processes of the thicklip grey mullet Chelon labrosus

This study aimed to identify the effects of water temperature on the rearing of the omnivorous teleost Chelon labrosus and to determine the optimal temperature for the culture of this interesting candidate for the diversification of European aquaculture. The fish (initial weight 26.81 ± 6.2 g) were held at four water temperatures (18, 22, 26 and 30 °C) in triplicate for 90 days in 100 L recirculating tanks ( n = 14 / tank). The effects of said temperatures were assessed on growth, intestinal health and the digestive processes of the fish. At 18 °C, energy consumption was low, leading to a high accumulation of reserves and slow growth, a typical overwintering strategy. The best growth results were obtained at 22 °C, followed closely by 26 °C, which resulted in low energy reserves. The fact that the fish at 26 °C grew less than the ones at 22 °C while having similar energy consumption, suggested that this temperature was close to the end of the optimal range, but no signs of stress were detected. However, at 30 °C the fish had lower energy reserves but grew significantly less, which can be considered indicative of stress. Health impairment at this temperature was confirmed by the epithelial lesions found in this group. The growth and energy availability of the different groups is discussed in the light of the activities of α-amylase, pepsin and alkaline proteases. As an integration of all these results, a quadratic regression model resulting from growth values (SGR) in relation to water temperature was performed, and it allowed predicting an actual optimal water temperature of 22.8 °C for growth of C. labrosus. This is the first assessment of the optimal water temperature for the culture of C. labrosus , and it will be highly valuable for the development of its intensive culture. • Optimal water temperature for the rearing of Chelon labrosus is 22.8 °C. • Slow growth and high energy reserve accumulation were found at 18 °C. • Some stress signs started at 26 °C, and temperatures of 30 °C were proven to impair animal welfare. • No significant alterations in flesh quality were detected on the tested temperatures.