Primary Studies On The Ecology Of Artificially Reared Larvae, Juvenile And Young Fish Of Southern Flounder, Paralichthys Lethostigma

Southern flounder, Paralichthys lethostigma , living in American inshore originally, was introduced into China for study and cultivation in the beginning of the century. This paper deals with the studies on growth, development and ecology of artificially reared larvae, juvenile and young fish of southern flounder, mainly including observation on morphology of development of larvae, juvenile and young fish, effects of light intensity on activity and survival rates of larvae, effects of diets component on survival rates of metamorphism of larvae, albinistic rates and survival rates of juvenile and young fish reared in different color containers, and adaptation of young fish to salinity, in order to develop technique of high yield artificial fry reared for southern flounder.Observation on morphology of development of larvae, juvenile and young fish of southern flounder. Morphology of larvae, juvenile and young fish of southern flounder are similar to that of Paralichthys olicaceus, but the development rate of southern flounder is fast evidently than that of Paralichthys olicaceus (for the rearing temperature of southern flounder,27.5—29.5℃,is higher), and the total length of southern flounder is shorter than that of Paralichthys olicaceus in the same developmental stage. Total length of newly hatching larvae of southern flounder are 2.16—2.28mm(N=30),average 2.22±0.06mm;total length of 25—34d larva are 7.9—10.8mm,average 8.9±1.5mm,and most of them have metamorphosed and become benthone;juvenile develop into young fish 34—44d after hatching with total length of 20.2—32.4mm.Effects of light intensity on activity and survival rates of larval southern flounder. There are significant effects of light intensity on activity and survival rates of larval southern flounder. Under nature light, most larva are aphototaxis and gather in shadow when the light intensity arrive to 1500 Lx. Survival rates of the larvae under light intensity of 500Lx,1000Lx,1500Lx,2000Lx and 2500Lx are 15.0 %,29.6%,38.3%,11.3% and 2.1% respectively(N=120, P<0.05). The feasible light intensity is 500—2000Lx and the optimal light intensity is 1000—1500Lx.Effects of diets component on survival rates of metamorphism of larval southern flounder. The particular size of diet firstly eaten by the fish was less than 100μm. The survival rates of metamorphism of the larvae fed on formulated diets, oyster eggs, rotifers(Brachionus plicatilis) and artemia nauplii are higher than that fed on diets do not contain formulated diets, survival rate of then are 34.2% and 25.4% respectively(N=120, P<0.05).Effects of container's color on albinistic rates of juvenile southern flounder. There are significant effects of container's color on albinistic rates of juvenile southern flounder(P<0.05). Albinistic rates of juvenile southern flounder reared in navy blue or black containers are lower than that of the juvenile rearing in white or yellow containers. Albinistic rates of the juvenile reared in black, navy blue, yellow and white containers are 20.8%,14.4%,57.6% and 86.6% respectively(N=100).Container's color do not affect the survival rates of the juvenile and young fish of southern flounder(P>0.05), survival rates of the juvenile reared in black, navy blue, yellow and white are 96.0%,90.0%,82.5% and 93.0% respectively. Albinistic fries are normal in growth and development.Adaptation of young southern flounder to salinity. Young southern flounder have high ability to adapt to salinity. In experiments of three groups of young fish with different total length(N=80), young fish with total length of 3.1—3.5cm and 3.6—4.1 cm can live in fresh water after 3 days desalination, and survival rates of them after 30 days culture are 98.6% and 100.0% respectively, similar to that rearing in normal seawater, and the growth rates are similar too(P>0.05). Survival rates of young fish with total length of 2.5—3.0 cm is only 90.0%(P<0.05) after 30 days culture. Therefore, 3.0 cm can be regarded as the critical total length of young southern flounder to adapt to fresh water.In this research, the systematical studies on the morphology of artificially reared larvae, juvenile and young of Paralichthys lethostigma in different development stage and the particular size of diet firstly eaten by the fish were firstly reported in China. The light intensity could affect the activity and survival rates of the larval southern was found in the research, which suggested that flounders could be fed best and then have high survival rate by using their characteristics of aphototaxis and gather in a certain light intensity. It is also found in this research that container's color had significant effect on the albinistic rates of juvenile southern flounder and that total body length of 3.0 cm can be regarded as the critical total length of young flounder to adapt to fresh water. The results above can enrich the biological theory of Paralichthys lethostigma rearing, facilitate the production techniques of artificial rearing in Paralichthys lethostigma or in other oceanic fish species, and provide some scientific data for the popularization of Paralichthys lethostigma.