Introduction
Despite the fast growth of aquaculture, there are still some bottlenecks to overcome towards a more sustainable and competitive industry. The high mortality rates of marine fish larvae, directly impact the number and quality of juvenile produced. During the larval stage most marine fish require live feed, for a correct development. Rotifers are great candidates for the early stages, as they have adequate size, slow movement, fast reproduction, and are easily cultivated. However, they are not nutritionally suitable for all marine species, and their enrichment is necessary. The green water technique consists on the introduction of microalgae in the larval tanks, as it creates a light diffusion pattern that facilitates the capture of prey and also enriches the live preys, providing essential nutrients to promote growth, survival, health, stress tolerance and reproduction. This work aims at the development of new formulations from microalgae towards the optimization of larval production, both to improve live feed and to increase larvae biological performance and stress response.
Methods
For the green water technique, a control (CTRL) with live Nannochloropsis sp. was compared to a group with Nannochloropsis sp. and Chlorella sp. supplemented with probiotics (NCp). Larvae of Argyrosomus regius were maintained for 18 days after hatching and growth and survival were analyzed. At this point, larvae were transported for 5 hours to induce stress. Larvae, from each treatment, were collected before and after stress to measure the impact of the treatments on oxidative stress by analyzing 1) enzymatic activity of oxidative stress enzymes and 2) gene expression of growth and stress markers. Larvae were also collected for microbiological analysis.
Results and Discussion
The use of the new microalgae formulation containing probiotics promoted a better survival compared to control (61.20 ± 15.79 % and 64.18 ± 9.31, respectively). Throughout the trial, there were no significant differences in the number of total marine bacteria and Vibrionaceae in the digestive tract of the larvae. Through analysis of antioxidant enzymes, growth, and stress genes it was observed that the use of probiotics significantly increased the tolerance of larvae to stress.
In conclusion, no deleterious effects were provoked by the supplementation and the enzyme activity and genetic analysis suggested a positive effect of the probiotics on the tolerance to an external factor, contributing to improve larvae biological performance.
Acknowledgments
This work was financed by the project ALLARVAE (ALG-01-0247-FEDER- 069971) and AQUARAS (MAR-02.05.01-FEAMP-0223).