Researching biological characteristics of black plaice, creating for research on artificial seed production to develop new species.
Black plaice has a scient name is Parastromateus niger, This is a species of the starfruit fish family(Carangidae), striped bass( Perciformes). In the world, the black plaice arrange in some areas: South Africa, Mozambique, Kenya, the Arabian Sea, Bengal bay, Indonesia, Phillippines, China, the South of Japan, and Australia. But the most diverse is the East seaside of India and Indonesia. In Vietnam, they distribute to the Gulf of Tonkin, Central, and East and South -West waters (Froese and Pauly,2014).
Black plaice is a predator, the main food is small invertebrates, juveniles, and crustaceans ( Pati, 1983; Dadzie,2007). This is the fish that has nutritional value and high economic is popularly exploited in many parts of the world and in Vietnam.
The reproduction season of black plaice
The result of analyses shows that coefficients of conditions of fish in research time fluctuating low from June to September(0.0272 ± 0.0006). The highest coefficients of conditions in October (0.0282 ± 0.0001). Gonado-somatic index (GSI) is highest in August (female fish 4.68%; male fish 1.29%). GSI is lowest in April ( female fish: 1.52%, male fish: 0.59%). Gonadal maturation rate of female fish and male fish increase from June to October, highest in August (female fish: 64%; male fish: 82%).
This shows that the natural breeding season distribution on the coast of Soc Trang-Ca Mau from June to October, breeding is concentrated in August of the year. The absolute fertility of black plaice estimates from 21.756 to 1.748.151 egg/individual. The relative fertility of black plaice 629 eggs/fish with the weight of the body from 237,52 to 1.491.00g/individual. A low correlation is found between absolute fertility and the weight of the fish body (r=0,51).
The result of the research shows that: the black plaice located at Soc Trang -Ca Mau beach area that started the breed season later than black plaice in the Arabian Sea (Dadzie et al., 2009).
According to Dadzie et al (2009), the temperature of the Arabian Sea change from 28 to 36 degree from June to October while this time in the coast of Soc Trang-Ca Mau, there is a strong southwest monsoon, causing heavy rain, and the water temperature fluctuates from 28-30oC (Mai Viet Van, 2014 and Do Ngoc Quynh, 2010). Because distribute at the environment with lower temperature so the fish had time to spend total heat accumulation time matures more slowly, so fish have a later breeding season.
The stage development of the ovary
Stage I: The ovary separated to 2 lobes small fibrous, has a slightly clear chalk pink color
Stage II: The ovule increases in size and bright yellow.
Stage III: The ovule increases rapidly in size, the ovule swells and thickens, small blood vessels appear on the surface. The color of the ovule changes from bright yellow to light yellow. With the naked eye, can be seen the egg particles located inside the egg cavity membrane.
Stage IV: The ovule is well developed and the segment is not clear. There are many blood vessels distributed on the surface of the ovule. The ovule is light yellow in color. The oocyte inside the egg membrane is easy to see with the naked eye.
Sliced oocyte stage 1 Sliced oocyte stage 2
Sliced oocyte stage 3 Sliced oocyte stage 4
The stage development of spermatorrhoea
Stage I: Spermatorrhoea is filamentous, has small lobes, is white in color, is close to the spine of the fish body. Eye observation cannot determine the sex of the fish. Histological analysis in the presence of cytoplasm, a large number of granulocytes are located in the follicular cells. Only pale pink capture cells of Eosin dyes were found on the slice.
Stage II: Spermatorrhoea increase in size and pale milky white. The appearance of sperm in the cyst (blue-purple color of hematoxylin). The appearance of spermatic vesicles containing spores. This stage has not seen the appearance of sperm. increase in size and pale milky white. The appearance of sperm in the cyst (blue-purple color of hematoxylin). The appearance of spermatic vesicles containing spores. This stage has not seen the appearance of sperm.
Stage IV: Spermatorrhoea increases in size compared to stage II, has an opaque white color. It is enlarged, its surface is bulging and rounded, visible to the naked eye contains much-colored sperm like milky white.
Histological analysis of this stage found that the sperm had escaped from the cyst and was filled with vas deferens and glands. On the slice showed that the sperm-containing glands have a very clear bluish-purple color with hematoxylin.
The results from the research provide new information on the biological characteristics of this species, which facilitates the study of the artificial breeding of this fish to develop the cultured species. The reproductive power of the black pompano is high so it is favorable for the exploitation of this fish all year round. However, fishing activities should be avoided during the breeding season, in order to help the fish regenerate natural populations.
Mai Viet- Can Tho university