Rearing environment affects growth and behaviour of sole, Solea solea

Sole is a soleid flatfish which special benthonic habits are a major challenge in aquaculture where appropriate husbandry conditions are not yet mastered. In nature, sole spend long times buried in sand, show low diurnal activity and nocturnal foraging probably to reduce predation risk. Therefore, it is hypothesized that individual variation in behaviour and activity, may determine individual variation in feed intake and thereby variation in growth of sole. The potential role of (non-) feeding behaviour in growth of sole suggests an influence of environmental factors (e.g. food type, feeding method, presence of substrate, light intensity /photoperiod, temperature). The objective of the current experiment is to assess the impact of environmental factors on behavior, growth and the phenotypic relationship between them in sole (Solea solea). Environmental factors assessed were selected based on characteristics which are different in nature compared to present intensive aquaculture systems of sole: barren bottom (B) versus sandy bottom (S) tanks; live ragworms (R) versus dry pelleted food (P); and outdoor/variable (O) versus indoor/controlled (I) environmental conditions (light/ photoperiod and temperature). Fish were randomly assigned to one of the 6 combination of treatments studied: SR, SP, BP in outdoor and SR, SP, BP in indoor conditions. There were four replicates per treatment, so in total 24 tanks. Each tank hold 20 sole with an initial body weight (meanof 50g. The total duration of the experiment was of 6 weeks. At the beginning of the experiment all fish were individually tagged, and weighed while anesthetized. Once a week behavioral recordings were conducted during the day on the different tanks (5min/tank). At the beginning and at the end of the experiment a novel environment test (10min/fish) was performed to 8 fish per tank in order to assess if individual variation in behavioral responses are related to variation in growth and if that relationship is context dependent. This study showed that variability of environmental conditions such as temperature and light intensity present in outdoor conditions reduce activity of sole during the day and result in lower growth, especially when fish are fed with ragworms (Environment*feed, P0.05).