Study On Biology Of Paralichthys Lethostigma During Early Developmental Stage

In this dissertation, the biology of Paralichthys lethostigma during early developmental stage were focused, the mainly areas are follows: study on early development of P. lethostigma; feeding habits and growth of larval,juvenile and young P. lethostigma; effects of light on feeding, growth and survival of larval P. lethostigma; effects of temperature and salinity on growth and survival of young P. lethostigma. The major obtained results were as follows:The morphological characteristics of early development of P. lethostigma were described in December 2006 and during January and February 2005. The average total length of newly hatched larva was 2.73±0.211mm. At the water temperature of 20.5±2.5℃and the salinity of 33.5±0.5, the embryonic development took 7 days to develop into pre-larvae, and then took another 23 days to develop into post-larvae. The mouth could be seen 6 days after hatching. The juvenile stage developed from 31 to 45 days after hatching. After 46 days, the fish developed into the early young fish period. Appear and disappear of crown-like fin, shift of right-eye and transformation of body coloring matter is the most obvious changes during early development of P. lethostigma. In addition, explore the differences of P. lethostigma and other flounder on morphological characteristics, and the dangerous period in the process of growth and development of larval, juvenile, young P. lethostigma.The ecological method was adopted to study the feeding habits and the growth of larval, juvenile and young P. lethostigma from December 2006 to February 2007. The results show that the larvae began to feed on the sixth day after hatching at water temperature of 20.5±2.5℃. The initial diet is rotifer. With the growth of larval, juvenile and young P. lethostigma, Artemia -nauplii could be fed in proper order. Based upon the determination of 288 individuals, the percentage of stomach with food was 83.0%, the plump coefficient of stomach was 0.9%～6.6%, and the dial feeding amount was 6.8%～29.6% of the body weight of larval, juvenile and young P. lethostigma. Rhythm of feeding intensity was obviously different during the day and night. The higher feeding intensity of larval fish was at 12:00 p.m and 8:00 a.m. the next day. Juvenile fish was at 10:00a.m.～17:00 p.m. and that of young fish was at 12:00 p.m., but it keep higher feeding intensity at 12:00p.m.～20:00 p.m.. Young fish fed also in the darkness of night,larval and juvenile seldom do. The time for feeding from empty to full in stomach, the average amount of food in full stomach, and the time for digesting food from full to empty in stomach by larval,juvenile and young P. lethostigma were determined in the present paper. The effects of light on the feeding, growth and Survival of larval P. lethostigma were studied. The light intensity suitable for feeding ranges from 10lx to 600lx.The larvae grow more fast, have more high survival rate,and more short feed conversion period in the appropriate light. It is not conducive to the growth and development of the larvae under too strong or too weak illumination. Most of the 27-day-old larvae died from starvation in dark conditions. In production, an appropriate extension of illumination at night can be shortened breeding cycle.The effects of temperature and salinity on growth and Survival of young P. lethostigma were studied. The proper temperature of young P. lethostigma range is15~30℃, the most suitable temperature range is18~27℃; Proper salinity degree range is0~36, the most suitable salinity degree range is 6 ~30.The young P. lethostigma grow more fast, have more high survival rate under the proper temperature. It is not conducive to the growth and development of the young fish under too high or too low temperature. It seemingly more beneficial to the growth and survival of the young fish under low salinity(6~18). In production, it should artificial elevate the temperature when the cultivate temperature lower than 15℃. It has active signification to promote the young P. lethostigma'growth and survival.