Towards optimisation of fish larval nutrition: the effects of new components in microdiet composition and feeding practices on larval digestive physiology
Optimisation towards fish larval nutrition were studied to facilitate the replacement of live feeds (rotifers and Artemia nauplii) as first feed. The first experiment in this thesis evaluated the impact of different dietary treatments on the diurnal digestive tryptic enzyme activity in gilthead sea bream (Sparus aurata) larvae. In order to evaluate optimum feeding time and frequency, several short-term experiments were conducted at different ages with different dietary treatments such as traditionally used live feeds (rotifers and Artemia) and microdiet. The results suggested that no matter what kind of diet was applied, sea bream larvae have a limited digestive capacity at some point in time during the day. The second study investigated the effect of different substances that potentially can enhance the trypsinogen production and secretion in various age stages of sea bass (Dicentrarchus labrax) larvae via tube-feeding method. The results showed an increase in tryptic enzyme activity after injection of phytohaemagglutinin, protein concentration, Calanus meal (Calanus finmarchicus) and the extract of the commercial microdiet MiniPro in sea bass larvae supported the hypothesis that selected substances can trigger the release of trypsinogen at specific developmental stage. The final study of this thesis focused on the potential of a product sourced from freeze-dried Calanus meal as a major component, as well as trypsin and pancreatin as digestive enzyme supplements in microdiet for sea bass larvae. The main goal of this experiment was to compare and evaluate the ontogenetic development of tryptic enzyme activity in larval sea bass fed either live feed, a commercial microdiet or the microdiet containing the Calanus meal as major ingredient. Results suggested that Calanus meal and pancreatin as a mixture of various enzymes and trypsin could effectively replace fish meal in sea bass larvae diets to achieve higher growth, tryptic enzyme activity, and survival rates.
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