Use of Copepods in the feeding of sole larvae Paralichthys orbignyanus (Valenciennes, 1842) and optimization of the cultivation of the copepod Acartia tonsa Dana, 1849
The experimental cultivation of the sole Paralichthys orbignyanus has been developed at the FURG Marine Aquaculture Station, Rio Grande - RS, with relative success. However, the high mortality rates observed in larvicultures using rotifers and brine shrimp as live food, have limited large-scale cultivation. Current studies have shown that copepods have good potential as an alternative live food, but existing cultivation methods still need improvement. Therefore, the objectives of this work were to test the use of copepod Acartia tonsa as exclusive live food in the larva of P. orbignyanus, and also to contribute to the improvement of the cultivation method of A. tonsa, through the evaluation of different diets and algal densities on egg production of this copepod. P. larvaeorbignyanus were grown in a 50 L tank (S = 30, T ° C = 22) for 22 days after hatching (dae). Nauplii of A. tonsa were offered as live food between the 3rd and the 19th “dae” while copepodites and adults were added from the 20th “dae”. In order to test the influence of different algal densities on the egg production of A. tonsa, the diatom Thalassiosira fluviatilis was supplied at densities of 0, 5,000, 10,000, 20,000, 40,000 and 80,000 cel mL-1. To evaluate the influence of different diets on egg production, two microalgae, Nannochloropsis occulata and Chaetoceros mulleri, and an inert commercial diet were used. The results showed that the sole larvae effectively fed A. tonsa completing the metamorphosis between the 19th and 22nd days.The standard length (mm) of the larvae on the 7th day was 2.98 ± 0.20, 4.77 ± 0.24 on the 14th day and 4.90 ± 0.42 on the 22nd day. The production of A.tonsa eggs was directly influenced by the increase in the concentration of T. fluviatilis, the highest value being obtained in the concentration of 80,000 cel mL-1 (~ 60 female eggs-1 24 h-1). Regarding the egg production test under different diets, it was observed that both the inert food and the microalgae N. occulata were ineffective, providing a very low egg production (~ 1 - 2 female eggs-1 24 h-1). The diet composed by the diatom C. mulleri, provided a production of 22 female eggs-1 24 h-1, representing a good alternative food for the cultivation of A. tonsa. In addition, its size (~ 7 # m) allows the feeding of both nauplii and adults, facilitating the cultivation of this copepod.