Introduction
The production of high quality and healthy fish larvae and juveniles is an important target for the successful and competitive growth of the aquaculture industry. Still, most marine fish larvae produced under intensive rearing conditions are known to be affected by several afflictions, including low survival rates and a high incidence of skeletal anomalies. Amongst other factors, nutrition has a key role in skeletogenesis. While taking advantage of an industrial setting, we performed the nutritional optimization of a commercial-type larval feed in terms of vitamins and minerals, that can be potentially be used as a tool to mitigate skeletal anomalies relevant for fish welfare and production.
Materials and methods
A series of larval fish nutritional trials were performed, using as base feed formulas, commercial larval fish feed products available from SPAROS Lda. Several nutritional feed component modifications were performed: Ca:P ratio; Inorganic Vs. Organic mineral forms; Dietary levels of Mn and Zn; Selected B-Vitamin supplementation; Choline removal from premix. Growth (Dry weight, standard length, relative growth rates (RGR)), survival, economic (feed conversion ratio (FCR)) and bone status (Figure 1) criteria were assessed.
Results
The omission of calcium supplementation, that can have a potential antagonist effect on the bioavailability of other minerals and/or nutrients, from the premix used in larval feed lead to the observation that a low Ca:P ratio, ranging between 0.5 and 0.7, is adequate to support a high survival and growth performance in Senegalese sole post-larvae, without compromising bone development and skeletal formation.
The replacement of inorganic mineral forms (sulphates) of Cu, Fe, Mn and Zn by their organic glycinate-chelated forms, did not generate marked beneficial effects on somatic growth and bone development in Senegalese sole post-larvae fed high quality commercial microdiets.
Dietary levels of Mn (90 mg.kg-1) and Zn (130 mg.kg-1) could help improve larval survival, decrease the severity of vertebral malformations, and increase the deposition of Mn in bone.
B-Vitamin supplementation (B1, B6 and B12) to larval feeds brings no clear advantage in attempting to enhance the growth performance and bone status of Senegalese sole larvae.
Although choline supplementation to vitamin premixes can decrease their stability, it is still necessary when feeding Senegalese sole larvae as, it’s removal can reduce growth criteria.
Conclusion
The conclusions obtained throughout this work demonstrate that mineral and vitamin levels and/or forms in commercial formulas are adequate for proper growth and bone development. Still, there is room for further nutritional optimization of inert microdiets when the potential beneficial effects of beyond requirement levels are considered and their impact on bone, immune and stress coping status of early-stage marine fish.