Whiteleg shrimp (Litopenaeus vannamei) may prefer warmer temperatures than commonly used in commercial farming: implications for animal welfare

The whiteleg shrimp (Litopenaeus vannamei) is the world's most abundant farmed aquatic species, but relatively little is known about its welfare needs, particularly in relation to its preferred temperatures in recirculating aquaculture systems (RAS). Existing guidance on rearing temperatures is typically based on thermal tolerance and optimal growth, as opposed to individual thermal preferences. We assessed individual variation in temperature preferences in the whiteleg shrimp over 24 h using a volitional shuttle box, a method that allows individuals to dynamically regulate their ambient temperature, providing more robust estimates of thermal preferences than static choice methods. The median preferred temperature of L. vannamei (T pref ) ranged between 29.2 °C and 32.8 °C, depending on body size, with smaller shrimp (<6.5 g) showing less variation and preferring significantly warmer temperatures than larger individuals (>10 g; quantile regression t 28 = 7.43, SE = 0.502, P < 0.001). The upper avoidance temperature (Avoid high ) was 32.2 ± 1.22 °C and the lower avoidance temperature (Avoid low ) was 30.3 ± 1.96 °C, which is 1–5 °C warmer than the temperature typically recommended for shrimp farming in RAS. Our study shows that individual whiteleg shrimp differed by as much as 13.7 °C in their preferred temperatures, and suggest that some commonly used rearing temperatures may be too low for the species, particularly in the case of smaller individuals, which are more likely to experience thermal stress. We recommend that welfare guidelines take into account thermal preferences and not merely thermal tolerance or temperatures associated with optimal growth. • The preferred thermal optimal envelope of L. vannamei can be estimated to lie between 29.16 and 32.83 °C. • Individuals vary significantly in their ability to thermo-regulate. • Weight significantly affected temperature preference, with smaller shrimp favouring warmer temperatures than larger shrimp. • The study is limited by the length of the recommended assay time (24 h), and the constraints that this imposes on sample size.