Bae-Ik Lee

Effects of Estradiol-17β on the Feminization of Japanase Eel, Anguilla japonica

The effects of oral administration of estradiol- (E2) on glass eels (Body weight: , Total length: ) and young eels (Body weight: , Total length: ) on gonadal sex and growth were examined, respectively. Glass eels were fed a diet containing E2 at a dose of 10 mg/kg or 25 mg/kg, respectively, for five months. The female ratio significantly increased in all E2-treated groups (10 mg/kg diet group: 70%; 25 mg/kg diet group: 90%) when compared to the control group (10%). Young eels were fed a diet containing E2 at a dose of 25 mg/kg for four months. The female ratio also significantly increased in the E2-treated groups (60%) compared to the control group (20%). The highest female ratio was observed in the stage of glass eels rather than young eels. In all experiments, however, the growth of eels treated with E2 was similar to that of controls to the end of the experiment. Thus, oral administration of E2 could be a good approach to controlling sex differentiation.

The Optimal Salinity and Temperature Condition for the Growth of Rotifer, Keratella sp.

Abstract We investigated the optimum salinity and temperature conditions for the mass culture of small rotifer, Keratella sp.. In the salinity experiment ranging from 0-34‰, the population growth of Keratella sp. drastically increased continuously up to 15‰, and then slightly increased over 20‰. Their maximum density reached 1,007 inds./mL at 0‰. A pre-reproductive phase was shorter in low salinity than in high salinity. The highest number of offspring per female (10.2 inds.) and lifespan of the female (10.7 days) were obtained at 0‰, but there were no significant differences compared to those at 5‰. In the temperature experiments ranging from 16-32℃, the highest maximum density (1,766 inds./mL) was shown at 24℃. The number of offspring per female significantly increased with increasing temperature, and the highest number of offspring per female was 10.4 inds. at 24℃. The lifespan of female increased with decreasing temperature and the longest lifespan was 12.8 days at 16℃.Key words : Small rotifer, Keratella sp., Salinity, Temperature Corresponding author : 033-640-2345, telss88@naver.com * 2013 (RP-2013-AQ-169) .

Effects of Water Temperature and Estradiol-17β on the Sex Ratio and Growth of the Japanese Eel, Anguilla japonica

This study investigated the effects that water temperature and the administration of estradiol-17s (E2) had on the sex ratio and growth of the Japanese eel, Anguilla japonica. Glass eels (total length≒6.5 cm) were differentiated into an E2 group and an E2-free group and then they were reared for about four months at three water temperature levels of 20C, 24C, and 28C. The results showed that the young eels survived normally at the rearing water temperature of ≥24 o C, and grew to a mean size of 20 cm (total length). In the E2-free group, temperature was not found to increase the sex ratio (feminizing rates); however, the sex ratio of the E2-administrated group was found to be a little higher at a high temperature (28C). The growth of the E2 group was lower than the growth of the E2-free group at 24 o C and the E2 concentration levels in the plasma at 24 o C were found to be significant after the end of the E2 administration period (178 days). Therefore, we thought that long-term administration of E2 must be considered to be the reason for growth decline in spite of the prominent sex ratio effect. Our results indicate that temperature was not related to an increase in the feminizing rate (sex ratio) in the Japanese eel, Anguilla japonica, and other environmental factors (rearing density, salinity, etc.) that have the possibility of inducing ovarian differentiation must be investigated.

Optimal Food and Concentration for Growth of Small Rotifer, Proales similis

This study determined the optimum microalgae species and concentration for growth of small rotifer Proales similis, in community cultures by feeding it several different foods. Four single trials (Tetraselmis suecica, TET; Isochrysis galbana, ISO; Nannochloropsis oculata, NAN; freshwater Chlorella vulgaris, CHL) were conducted at 5 psu and 25 . The maximum density and specific growth rate (SRG) were ℃ highest for rotifer fed CHL reaching 1,075 individuals (inds.)/mL and 0.83 respectively. By contrast, other foods of ISO, NAN and TET resulted in poor growth rates and maximum density. In the freshwater C. vulgaris experiments examining a range of 0.05 to 8.8 mg/10 4 rotifers, the growth of rotifer tended to decrease with the amount of supplement. The maximum density and SGR of females was highest at 910 inds./mL and 0.55 respectively, at 0.05 mg/10 4 rotifers. These results suggest that the best microalgae species for the culture of P. similis is freshwater C. vulgaris and the optimum concentration is 0.05 mg/10 4 rotifers.

Digestive Physiological Characteristics of the Gobiidae

In this study, we investigated the characteristics of CCK-producing cells and mucus-secreting goblet cells with respect to stomach fish and stomachless fish of the Gobiidae in order to provide a basis for understanding the digestive physiology. Hairychin goby (Sagamia geneionema), which is stomachless fish, the numbers of mucus-secreting goblet cells is highest in the posterior intestine portion (P<0.05), while CCK-producing cells are scattered throughout the intestine. Gluttonous goby (Chasmichthys gulosus), which is stomach fish, mucus-secreting goblet cells are most abundant in the mid intestine portion (P<0.05), whereas CCK-producing cells are observed only in the anterior and mid intestine portion. Trident goby (Tridentiger obscurus) which is stomach fish, mucus-secreting goblet cells were most abundant in the mid intestine portion (P<0.05). CCK-producing cells are found in the anterior and mid intestine portion. Giurine goby, Rhinogobius giurinus which is also stomach fish, the largest number of mucus-secreting goblet cells showed in anterior intestine portion except for esophagus (P<0.05). CCK-producing cells are present only in the anterior and mid intestine portion. In S. geneionema, digestive action occurs in the posterior intestine portion to protect and functions to activate digestion. In contrast, in C. gulosus, T. obscurus and R. giurinus, their digestive action occurs in the anterior and mid intestine portion to protect and functions to activate digestion. Further studies of the modes of food ingestion by these fish, the contents of their digestive tracts, and the staining characteristics of the goblet cells need to be carried out.

Development Changes in the External Structure of the Head and the Histological Structure of the Eye in Artificially Reared Japanese Eel, Anguilla japonica, Leptocephalus and Glass Eel

Knowledge of morphological changes in eel larvae is very important for artificial rearing of eel larvae. In this study, we investigated the morphological structure of the head region and histological changes of the eye retina in artificially reared larvae at various stages and in glass eel just after metamorphosis. Structural changes were observed in the upper jaw (maxilla) and the lower jaw (mandible) after 100 dah (day after hatchery) and after metamorphosis. Teeth had degenerated by the time of completion of metamorphosis. Major histological changes observed in the eye retina were the formation of the outer plexiform layer and the outer nuclear layer from 100 dah larva and a change in the rod cell layer after metamorphosis. The cornea was not observed at 10 dah in the eel larva. More information is needed on the early developmental stages of eel larvae to enable mass production of glass eels. The results obtained in the present research will be useful when developing novel rearing programs for eel larvae.

Effect on Enrichment with Schizochytrium sp. and Squid Todarodes pacificus Liver Oil on Fatty Acid Content of Live Feed

We investigated the effects of enrichment with oil or bacteria on the fatty acid composition of rotifers and Artemia as live prey. One enrichment(oil source) was mainly composed of squid Todarodes pacificus liver oil; the other(photosynthetic-bacterial source) was primarily made up of Schizochytrium sp. The enrichments were intended to enhance the nutritional value of the live prey, such as their EPA, DHA and n-3 HUFA contents. The lipid content as EPA and DHA of rotifers was higher when enriched with the oil source rather than the photosynthetic-bacterial source. The DHA content of Artemia nauplii after enrichment differed significantly, depending on the type of enrichment used(P

Morphological Observation of Pre- and Postovulated Eggs from Artificially Maturated Wild and Feminized Eels

This study about morphological observation of preor post ovulated eggs obtained from artificially maturated female eels. Female eels were divided with two groups as wild eels from nature and feminized eels from farm. Artificial maturation had been conducted with the established methods in this laboratory, and then maturate eggs sampled at fixed 3 times and these were observed with stereomicroscope. Rate of increased body weight (RIW) were measured with 2 times. Egg diameters and development of oil droplets are determined for standardization of egg maturation degree, and the transparency of egg cytoplasm and the homogeneous degrees of egg size were referred to determine of egg quality. Rate of increased body weight (RIW) were good in range about 10 % at final salmon pituitary extracts (SPE) injection time and in range about 20 % at 17 , 20 -dihydroxy-4-pregnen-3-one (DHP) injection time. Good matured egg for α β fertilization had 900-1000 diameter, and they had about 50 oil droplets in size about 100 diameter. μm μm There were not predominant differences at egg size and oil droplet development between wild female and feminized eels

Optimal Salinity and Temperature Conditions for Mass Culture of Small Rotifer, Proales similis

Abstract We investigated the optimum salinity and temperature conditions for the mass culture of small rotifer, Proales similis. In the salinity experiment ranging from 1, 5, 10, 15, 20, 25 and 33‰, growth tended to decrease with salinity increase. Most agreeable salinity for rotifer growth was 1‰ in which maximum density and specific growth rate (SGR) were obtained. In the temperature experiments ranging from 15, 20, 25, 30 and 35℃, continuous growth of rotifer populations was found up to 35℃. The highest maximum density (2,060 inds./mL) of rotifer was observed at 25℃ in given temperature regime. Also, the SGR of females showed increasing tendencies with the increase of temperature. These results suggest that the optimum salinity and temperature for mass culture of P. similis may be 1‰ and 25℃, respectively.Key words : Small rotifer, Proales similis, Maximum density, Salinity, TemperatureCorresponding author : 033-640-2345, telss88@naver.com 2014 (RP-2014-AQ-092) .

Comparative Study of Digestive Enzyme in the Artemia Feeding Step of the Sweet Fish Plecoglossus altivelis, Rock Fish Sebastes schlegeli, Black Seabream Acanthopagrus schlegeli, and Olive Flounder Paralichthys olivaeus

We compared the nutritional requirements of whole larvae of the black seabream Acanthopagrus schlegeli, sweet fish Plecoglossus altivelis, olive flounder Paralichthys olivaeus and rock fish Sebastes schlegeli. The larvae were 20, 30, 14 and 5 DAH (or spawning) of black seabream, sweet fish, olive flounder and rock fish, respectively. Specific α-amylase activity (mU/mg protein) was highest (8,324.9 mU/mg protein) in rock fish larvae (P<0.05). Specific trypsin-like protease activity was highest (11,330.1 mU/mg protein) in black seabream larvae (P<0.05), which also exhibited the highest activity, 685.5 mU/mg dry weight (P<0.05). The specific activities per mg protein and mg dry weight of black seabream were the highest (187.4 mU/mg protein and 11.3 mU/mg dry weight, respectively) (P<0.05). A/P, P/L and A/L ratios of rock fish were 1.47, 90.3 and 133.1, respectively (P<0.05). We present here basic larval digestive enzymatic nutritional requirement data.