Qtae Jo

Sterol composition of dark-grown Isochrysis galbana and its implication in the seed production of Pacific oyster, Crassostrea gigas

Isochrysis galbana was cultured heterotrophicallywith glucose and mannose as a potential food for larval Pacific oyster,Crassostrea gigas. The food was evaluated in terms offeeding experiments and changes in sterol composition. The larvae showed delayedgrowth and higher mortality compared with ones fed light-grown material, with asignificant difference in mortality from day 8. Light-grown I.galbana contained three major sterols (24-oxocholesterol acetate,ergost-5-en-3β-ol, and cholest-5-en-24-1,3-(acetyloxy)-,3β-ol) and twominor sterols (24-methylcholesta-5,22-dien-3β-ol and24-methylcholest-5-en-3β-ol). The sterol content decreased markedly aftertransfer to dark culture, especially in two of the major sterols,24-oxocholesterol acetate and ergost-5-en-3β-ol. The other major sterol,cholest-5-en-24-1,3-(acetyloxy)-,3β-ol, fall to about 50% of theautotrophic control by day 12. These results indicate that heterotrophicallygrown I. galbana is not a favorable alternative to normallygrown material for larval C. gigas culture as far as sterolcomposition is concerned.

Eyestalk ablation-induced androgenic gland activity and gonad development in the freshwater prawns Macrobrachium nipponense (De Haan, 1849)

Summary Effects of eyestalk ablation on androgenic gland (AG) protein synthesis and the following gonad development were determined in reproductive and non-reproductive adult males of the freshwater prawn Macrobrachium nipponense. During the non-reproductive season, the AG cells from intact prawns were characterized by a small amount of vacuolated cytoplasm and highly pycnotic nuclei. The AG cells from unilateral eyestalk ablated prawns (UEA) consisted of developing rough surfaced endoplasmic reticulum (rER) a molting cycle after the operation. The AG cells of bilateral eyestalk ablated prawns (BEA) showed a more extensively developed rER and Golgi complex, which are similar in appearance to AG cells from normal reproductive prawns. The gonads from reproductive prawns were in active spermatogenesis. Eyestalk ablation prompted the progress, particularly in the BEA. The gonads from non-reproductive prawns were under reproductive arrest. The eyestalk ablation induced the non-reproductive prawns to be reproductive. The reproductive performance induced by BEA was as successful as in the normal reproductive prawns in terms of gonado-somatic index (GSI). The GSI of the phased changed prawn was 1.21 whereas the GSI of normal prawns during the reproductive season was 1.10. These data taken together with the AG cell changes suggest that eyestalk ablations appear to induce precocious male gonad development by stimulating AG cells from the prawn.

Analysis of Population Distribution on Stocking Area of Sandy Beach Clam, Gomphina melanaegis

The clam, Gomphina melanaegis, which is commonly called the sandy beach clam because of its habitat, is a valuable organism in the sandy coast of East Sea, Korea. It is frequently observed in large populations between 0.5 and 5 meters. We have released 50,000 seedling, ranging from the diameter of approximately 3 mm, 2007, and 1,000,000 seedling, ranging from the diameter of approximately 0.2 mm, plus 100,000 adult individuals, ranging from the shell length of approximately 20~40 mm, 2008 at Jinha beach. The spawning period of G. melanaegis, was from June to August, and the main spawning occurred in July. This investigation was carried out to elucidate population distribution on the stocking area of sandy beach clam, G. melanaegis. The relationship between shell length and ring radius in each ring was investigated as a regression line. The relationship between the shell length and shell height of released young clam was SH=1.0105SL-4.7764 (). The relationship between the shell length and total weight of released young clam was (). It draws a deduction that the ring of this clam was produced once a year during the duration between June and August