Different early weaning protocols in common sole (Solea solea L.) larvae: Implications on the performances and molecular ontogeny of digestive enzyme precursors

The effects of early weaning on the performances and molecular ontogeny of digestive enzyme precursors in common sole (Solea solea) larvae were studied. Four experimental weaning time protocols (WPs) were performed in triplicate. One protocol was used for the control group where larvae were fed live feed until 27 days post-hatching (dph) (WP-27) and weaned with dry feed. The other groups provided only with dry feed (WP-4), live feed until 13 dph (WP-13) and live feed until 18 dph (WP-18), followed by weaning on to the same commercial microdiet (MD) used in the WP-27 group (AgloNorse K/S Tromsø Fiskeindustry A/S & Co., Norway). The trial lasted until 33 dph. The larvae of the WP-4 group displayed a significantly lower survival rate, lower growth increase and a delay in the onset of metamorphosis when compared with the other groups. The WP-13 and WP-18 groups displayed significantly lower weight increases when compared with the WP-27 group, whereas metamorphosis development and survival were not in fluenced. Partial transcripts of trypsinogen 1 (tryp1), trypsinogen 3 (tryp3), trypsinogen Y (trypY), chymotrypsinogen (chymt), amylase (amy) and hepatic lipase (HL) were cloned and analysed by quantitative real-time PCR (qPCR). The tryp1 and chymt mRNA levels displayed a rapid increase in all the treatments between 4 and 8 dph and thereafter displayed a homogeneous fluctuating pattern with a higher increasing tendency for chymt at the end of the trial. The amount of tryp3 and trypY mRNA remained stable or slightly increased until 27 dph in all WP groups and thereafter displayed a general up-regulation trend. The amy transcript levels displayed a gradual increase throughout the study in all WP groups. The HL mRNA levels increased until 13 dph in the WP-27, WP-18 and WP-13 groups and thereafter remained generally stable until 27 dph, whereas in the WP-4 group, there was a linear time-related increasing trend until the end of the trial.This study supports previous results on the feasibility of early weaning of common sole larvae using a MD before the end of metamorphosis.The molecular ontogeny of some important digestive enzyme precursors is described for the first time in this species. The transcripts analysed were not greatly influenced by the WPs.