강도다리와 돌가자미의 잡종 유도 및 양식 산업적 유용성 분석

Abstract

Intergeneric hybridization has greatly contributed to genetic and productive improvements in aquaculture. This manipulation technique has been widely used in various species of fish to improve disease resistance, growth rate and flesh quality, environmental tolerance and a various traits to make fish more profitable to increase. As starry flounder (Platichthys stellatus) is a cold-water breeder, which has strong disease resistance and euryhaline characteristics. Its production is rapidly increased recently. However, it takes more than two years for fish to fully grow-up to marketable size for high quality of "Sashimi". On the other hand, stone flounder (Kareius bicoloratus) has relatively good meat quality and flavor, but susceptible to high temperature, stress and disease. Therefore, seedling production of stone flounder is only made for releasing fry to improve stock resources in wild, but not for aquaculture in commercial scale farm. The purpose of this study is designed to examine the usability of hybrids between two species and investigate aquacultural effectiveness. The induced hybrid has floating type of eggs and first cleavage was conducted in 1 hour after fertilization at 12 ℃. Small sized Kupffer’s vesicle began to be observed in 46 hours and generated to full size in 51 hours after fertilization. They disappeared in 7 and a half hours, and then the tails were formed. The eggs started to hatch-out in 85 hours after fertilization. Five days after hatching, the larva absorbed most of the egg yolk and transformed to normal swimming position from the head lower position. Seven days after hatching-out, almost all entities started to eat rotifer. Eighteen days after hatching-out, Artemia nauplius started to be provided. 35 days after hatching-out, commercially available frozen copepod (Aquanet) were provided along with Artemia nauplius. About 50 days after hatching-out, the mixed feed of what was provided. In day 112 after hatching-out, they were grown to 5.5 to 7.8 cm in total length. In order to determine an optimal anesthetizing concentration for hybrid, the clove oil was used as the standard anesthetic and the time for anesthesia and recovery were calculated. As the concentration of clove oil increased, the anesthetizing time took about one to two minutes at 20∼80 ppm; however, the recovering time was not affected by oil concentration. The results of morphological analysis of induced hybrid showed that the proportion of the body length to the total length were 85.99, 85.51 and 87.14% for starry flounder, hybrid and stone flounder, respectively, which were not different from each other. The proportion of the body height to the total length were 48.56, 49.39, 44.74% for starry flounder, hybrid and stone flounder, respectively. The proportion of the caudal peduncle length to the total length were 8.55, 8.27, and 9.25% for starry flounder, hybrid, and stone flounder, respectively. The proportion of the caudal peduncle height to the total length were 9.48, 9.59, and 10.54% for starry flounder, hybrid and stone flounder, respectively. The proportion of the head length to total length was 26.83, 25.32 and 22.47% for starry flounder, hybrid and stone flounder, respectively. There was no morphologically significant difference between starry flounder and hybrid. The proportion of the upper chin length to the head length were 31.54, 32.85 and 33.70% for starry flounder, hybrid and stone flounder, respectively, which were not different from each other. The proportions of the snout length to the head length were 21.26, 21.16 and 19.75% for starry flounder, hybrid and stone flounder, respectively. The interorbital width to the head length were 7.43, 9.31 and 7.19% for starry flounder, hybrid and stone flounder, respectively. And the proportion the of eye diameter to the head length were 18.71, 22.71 and 17.76% for starry flounder, hybrid and stone flounder, respectively. There was no significant differences in measurement trait among three fish groups. The result of cytogenetic analysis of induced hybrid showed that the surface area and volume of the cell in hybrid were 38.11±4.30 μm2 and 136.07±45.51 μm3, respectively. The surface area and the volume of the nucleus in stone flounder, starry flounder and hybrid were 8.19±0.44 μm2 and 16.08±2.45 μm3. These values were identical to the values of two parents used in this study. The content of DNA were also 0.66 pg/haploid cell for all three groups. The result of the mid-term mitotic figure of female and male hybrids showed that the number of chromosomes were 2n=48 and the karyotype was consisted of 24 sets of acrocentric chromosomes. There were no differences in the number of chromosomes and the karyotypes between female and male starry flounder, hybrid and stone flounder. Moreover, the result of the nuclear organization regions (NOR’s) through silver staining showed that the NOR’s existed in one set of the smallest no significant differences (p<0.05) in measurement trait among three. There were no significant differences in daily growth rate, feed coefficient and condition factor in fry for starry flounder, hybrid and stone flounder in the 60-day feeding trial. However, after stocking hybrid and starry flounder in the same tank for 8 months, the hybrids showed 15.1% higher in growth rate and 12.0% in condition factor than starry flounder. The Scuticocidal activities were analyzed for three sessions for 4-month old starry flounder, hybrid and stone flounder. The result showed that starry flounder showed the highest tolerance and the lowest for stone flounder, respectively, whereas the induced hybrid showed the tolerance that is higher than the average of the two parent breeds. The starry flounder and the hybrid were fed to ad libitum daily. The two experiment groups were observed up to 24 hours. The result showed that there were no differences in cell cycles up to eight hours and after 12 hours, the cell cycle of the starry flounders became faster. The experiment group were not fed and observed from two days to two weeks. Up to 12 days after initial feeding, the cell cycle of starry flounders excelled faster than the right-eyed flounders. From day 14, the cell cycle of hybrids excelled. Salinity resistance test of starry flounders and hybrid was performed by lowering salinity of water from 35 psu to 2.5 psu. The result showed that one unit from each experiment group died which showed that both hybrid and the starry flounder were highly resistance to low salinity when salinity was gradually lowered. However, when the units were starved for two weeks and processed with fresh water, mortality of hybrid increased rapidly after three days and all units died after five days. All units that died showed bleeding in fins and failing of phlegm. The result of analyzing gDNA of PRL using tail fins of starry flounders, stone flounder and hybrids showed that the hybrid having two PRL genes that are different from one of each gene in starry flounder and stone flounder. The PRL expression was not present at 32 psu in starry flounders; however, the hybrid showed relatively low expression at 32 psu, and high expression at 6 psu. Starry flounder genes only were expressed in hybrids when exposed to low salinity. The ovarian tissues were analyzed for starry flounders and hybrids. Reduction division was observed in all groups. Therefore, the maturation for 19-month old hybrid was examined anatomically, and normal maturation was observed. There was no difference in moisture, crude protein and ash content in the whole body of starry flounder and hybrids, but crude lipid content in hybrid was higher than in starry flounder. There was no difference in free amino acid and fatty acid profiles, except for L-valine between starry flounder and hybrid. These results indicate that hybrid between starry flounder and stone flounder is expected to contribute to the improved profits in fish culture industry in Korea.