SPAWNING OF BONITO, SARDA SARDA, IN CAPTIVITY

Atlantic bonito, Sarda sarda, could be a new candidate to aquaculture for several reasons: it has a quick growth, reaching 1kg in a few months of life, it is capable of reproducing at the end of its first year of life and it is also a valuable and well known species. However, handling is difficult and although some similar species like Striped bonito, Sarda orientalis, and Pacific bonito, Sarda chiliensis, have been cultured, nobody has tried to culture Atlantic bonito before with aquaculture purpose. Atlantic bonito is a gonochoric species, with asynchronous oocyte development, which lead to several spawning batches. In early spring 2005, 19 bonitos were fished in Mazarrón Bay with a fishing trap called Almadraba. Bonitos got into the trap and they stayed alive until the net was lifted. Just in that moment, fish were caught with a rubber net and placed in a 2000 l tank with a closed water flow to create a stream water inside the tank. Then they were moved into a truck and brought to our facilities. Once in Centro Oceanográfico de Murcia, fish were placed in a 25 m3 black round tank (4m diameter and 2m depth). Bonitos started to eat a week later. They were fed with frozen fish: European anchovy (Engraulis encrasicholus), European pilchard (Sardina pilchardus), bogue (Boops boops) and Round sardinella (Sardinella aurita), supplied to satiation five days per week. A 25% mortality was recorded during the first week mainly due to fish injured by the rubber net and the fishing gear. In January 2006, a great storm did that the water into the tank became turbid, and bonitos started to scrape against the wall of the tank. This led to a 50% mortality of broodstock. In order to avoid this, a sand filter was placed in the water inlet for the rest of the experiment, and the 7 remaining fish survived until the spawning period. In late May, fish started to show courtship behaviour, with 3 males swimming behind a female. Then the water flow was changed to force surface water outlet. A 500µ net was placed in the outlet and it was checked daily. We obtained fertilized eggs on 8th, 11th and 14th of June. The total amount of eggs obtained was 301.000, with a mean fertilized rate of 16% (std 2.94%). The lack of courtship signals with another females and the little amount of eggs obtained, make us think that all the spawns came from only a female, but we cannot assure it. If it is so, the fecundity rate would be in agreement with other references. The obtained eggs had a diameter of 1030.7±17.4µ and a dry weight of 122.5 ± 3µg. The number of oil globules was variable, ranged between 2 and 14. The mean was 9.17 ± 2,28. Incubation was carried out in a 500 l cylindrical tank, with open flow and a temperature of 21-22ºC. The hatching of eggs took place in the second day after the collection of fertilized eggs. Fresh hatched larvae measured about 3.5mm and weighted nearly 80µg. Hatching rate was about 60%