Maturation performance of Penaeus vannamei co-fed with Artemia biomass.
Sofar, only few shrimp hatcheries are successful in the commercial propagation of captive broodstocks. Diets for successful maturation performance of Penaeus vannamei have typically relied on the inclusion of marine polychaetes from Panama or Maine-USA, which are expensive and have an unpredictable supply. Studies were therefore undertaken to substitute the polychaetes by frozen ongrown Artemia. Prior to the freezing, some batches of Artemia were bioencapsulated with specific oil emulsions. Feeding rates were 14-15% of the tank biomass (live weight) per day of non- or enriched Artemia biomass, as a replacement of the polychaetes. Control tanks received 10% of polychaetes or an extra 10% of squid.
Dietary effects on the reproductive performance of male and female broodstock were evaluated separately, and egg and larval quality characteristics were monitored. Results from the three experiments demonstrate that the use of enriched Artemia biomass in maturation diets gives an equal (USA-test) or even a better performance (Ecuador-tests) as when marine polychaetes are included. In the latter experiments the overall nauplii production increased even by 73%, respectively 189% when feeding non-enriched or enriched Artemia biomass instead of polychaetes. This was the result of increased numbers of reproductive females and spawns per individual female and a decrease of the number of infertile spawns; however, hatching percentages were 5 and 10% lower, respectively. It may therefore be concluded that (enriched) Artemia biomass may be useful as a substitution product for the polychaetes.
(Centro Nacional de Acuicultura e Investigaciones Marinas, Campus ESPOL 09014519, Guayaquil, Ecuador)
Control of viral nervous necrosis (VNN) in striped jack Pseudocaranx dentex larvae.
Viral nervous necrosis (VNN) is a newly-emerging disease in hatchery-reared larvae and juveniles of marine fish such as striped jack Pseudocaranx dentex in Japan. Unenveloped round-shaped virus particles, 25-30 nm in diameter, are packed in the cytoplasm of infected nerve cells. The causative agent of VNN in striped jack was identified as a nodavirus (Nodaviridae) and designated as SJNNV. Diseases of marine fishes similar to VNN were also reported in seabass, barramundi and turbot in Southeast Asia, Australia, and Europe respectively.
In the case of VNN in striped jack, the virus (SJNNV) was detected from gonads and eggs of spawners. Antibodies against the virus were detected from spawner's plasma, thus, elimination of spawners carrying the virus was thought to be effective to prevent the disease in larvae. Although removal of antibody-possessing spawners by ELISA-based diagnosis reduced the rate of disease occurrence, the disease still occurred in some larval groups obtained from antibody-negative spawners. This suggests that the absence of antibody did not necessarily mean the absence of the virus in spawners. In the next step, we applied the PCR amplification technique to detect the virus from spawner's gonads just before spawning and virus-positive spawners were eliminated from spawning groups. It was confirmed that this procedure was very effective for the prevention of VNN in the larval production. Presently, the PCR-based selection of spawners seems to be the best method to control the disease, although a negative PCR result does not mean complete absence of the virus in the whole body. Striped jack broodstocks are forced to spawn repeatedly in a spawning season and virus-negative fish at the initial spawning often turn to virus-positive after several spawnings. Therefore, it is also important to reduce the stress factors which will induce virus multiplication in fish.
(Faculty of Applied Biological Science, Hiroshima University, Higashi-Hiroshima 724, Japan)
