Effects of culture density and live prey on growth and survival of juvenile cuttlefish, Sepia officinalis
Résumé
The effects of culture density on growth and survival of juvenile cuttlefish were tested. Groups of 1, 3 and 5 hatchlings were placed in small containers with bottom surface of 80 cm2, obtaining individual densities of 125, 375 and 625 cuttlefish m−2, respectively. Additionally, groups of 5 hatchlings were placed in containers with 2 different bottom areas (80 and 240 cm2), providing culture densities of 625 and 42 cuttlefish m−2, respectively. A total of 120 hatchlings were used and experiments lasted for 40 days. No differences were found in growth between any of the densities tested throughout the experiment until 35 days old. After this, cuttlefish placed in isolation grew significantly larger. A second experiment was conducted in a flow through system, using two rectangular tanks with bottom surface of 0.5 m2. Two groups of 25 cuttlefish hatchlings were used in this experiment, which lasted for 40 days. Both groups were fed live juvenile shrimp (Crangon crangon) during the first 5 days. Afterwards, one group was fed live fish fry of different species, while the other continued to be fed shrimp. After day 10 and until the end of the experiment, hatchlings fed shrimp grew significantly larger than those fed fish fry. Survival of hatchlings fed shrimp or fish fry after 40 days was of 100% and 68%, respectively. Total protein content of both prey types was similar. Therefore, the higher polar lipid content, especially due to the higher phosphatidylcholine and phosphatidylethanolamine levels observed in the shrimp, compared to fish fry could possibly be one of the major factor to explain the significantly higher growth rates for S. officinalis juveniles fed shrimp. Also, the percentage of polar lipids in the shrimp (47.4%) was closer to the one of juvenile cuttlefish (38.1%) than the composition of polar lipids in fish fry (10.4%). This could also be an important factor to explain the poor growth and survival obtained when feeding fish fry to the cuttlefish.