Evaluation of very early weaning of common sole (Solea solea L.) using commercial diets: implications on performances, larval quality and tank hygiene

A study on common sole (Solea solea L.) larvae was carried out in order to assess the potential for a very early weaning onto commercial microdiets before the end of metamorphosis. Four days post hatching (dph) larvae were randomly allocated in twelve flat bottom (0.64 m2) 280 L square tanks (2000 larvae tank-1) connected to a recirculating system. Four experimental weaning feeding regimes (FR) were used in triplicate: Control (FR-C) where larvae are fed Artemia nauplii and metanauplii with dry feed until 27th dph. The others FR provided live feed until 13th dph, employing the same diet used in FR-C (AgloNorse Ewos, Norway – FR-A), Gemma Skretting, France (FR-G) and O.range Large INVE, Italy (FR-O). The trial lasted until 33rd dph. Data were subjected to statistical analyses using a General Linear Model, the ordinal regression and one-way analysis of variance (ANOVA) with Tukey’s post test. No significant differences among groups were observed in survival at the end of the trial. Groups subjected to very early weaning (FR-O, A and G) showed lower weight and length when compared to control, but that did not result in a delay in the onset of metamorphosis. Fatty acids profile of larvae was influenced by the FR. The total number of Vibrio spp. was higher in FR-C tanks at 21 dph, probably due to the presence of live feed in rearing water. Larval quality measured at the end of the trial by the salinity stress test was not influenced by treatments. In conclusion, very early weaning in sole affects growth potential but not survival and susceptibility to stress.