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.

In fish, light (photoperiod, intensity and spectra) is main regulator in many physiological actions including growth. We investigate the effect of light spectra on the somatic growth and growth-related gene expression in the rearing tiger puffer. Fish was reared under different light spectra (blue, green and red) for 8 weeks. Fish body weight and total length were promoted when reared under green light condition than red light condition. Expression of somatostatins (ss1 and ss2) in brain were showed higher expression under red light condition than green light condition. The ss3 mRNA was observed only higher expression in blue light condition. Expression of growth hormone (gh) in pituitary was detected no different levels between experimental groups. However, the fish of green light condition group was showed more high weight gain and feed efficiency than other light condition groups. Our present results suggest that somatic growth of tiger puffer is induced under green light condition because of inhibiting ss mRNA expression in brain by effect of green wavelength.

Light characteristics are very specific in the aquatic environment. Fish vision and different light spectra perception are related to each species’ natural habit. Light is one of the main environmental conditions and can be easily manipulated in artificial rearing settings. Mucus-secreting goblet cells are the main regulators of digestion. In this study, we established whether the light spectrum (natural condition, full spectrum: green, 520 nm; red, 590 nm, and blue, 480 nm) influences growth performance and digestive activity related to mucus-secreting goblet cell activity in order to develop a good management protocol and optimal rearing system for nursery stage of Epinephelus akaara. For each light spectrum, fish (11.5 ± 0.2 g in mean initial body weight, 9.0 ± 0.1 cm mean initial total length) were reared 16 weeks under a flow-through system and fed commercial pellet diets twice daily. At the end of the experiment, the final body weights differed among the fish reared under different light spectra. The highest growth performance value and feed efficiency were observed in fish reared under the green light condition. Mucus-secreting goblet cell activity was significantly higher in the fish under green light condition than in the fish under the natural, red, and blue light conditions. Rearing of E. akaara under the green light condition had positive effects on fish growth performance and digestion. We recommend that the appropriate light spectrum for nursery stage of E. akaara is the green light condition from the perspective of growth performance and the synergistic effects of mucus-secreting goblet cells. However, longer light treatment periods are needed in future investigations to clarify the effects of light spectrum on each growing stage of E. akaara.

As a preliminary investigation into the effect of environmental factors control for gonadal development, we examined the involvement of photoperiod and water temperature in ovarian development of Epinephelus. akaara. For the induction of sexual maturation, E. akaara reared in recirculating aquaculture system (RAS). During November 2013, the photoperiod and water temperature was adjusted to 12L:12D and 18℃, respectively. In the photo-thermal treatment group, every 3 weeks daylight was increased as follows a 13L:11D and 14L:10D, and control group was maintained under natural condition. After 9 weeks, water temperature was increased 23℃ in photo-thermal treatment group. The sampled fish every 3 weeks revealed increase in gonadosomatic index (GSI; 5.18±1.38), oocyte diameter and vitellogenic oocytes (423.9±36.1 ㎛) were observed in gonads 12 weeks under photo-thermal treatment group. However, ovarian development was maintained immature stage in control group. In this environmental factors manipulation trial, seventy one of the 95 females (578.4 ± 25.4 g in mean body weight, 31.0 ± 0.5 cm mean total length) treated with HCG injection (doses 500 IU/kg BW) were induced ovulation by artificial stripping. The total volume of ovulated eggs were 3,470 ml and the total volume of fertilized eggs was 3,295 ml. The fertilization rate and hatching rate were 95% and 98%, respectively. These results suggest that the photoperiod as well as water temperature are major environmental factors in triggering the gonadal development of E. akaara.

We investigated the change mRNA expression of GtHs subunits (FSHβ, LHβ) in the pituitary, androgen receptor (AR), estrogen receptor (ERα) in gonad and histological observation of gonads in longthooth grouper Epinephelus bruneus by treatment Femara, an aromatase inhibitor (AI). Longtooth grouper (body weight 408±43.1 g; one year) cultured in Future Aquaculture Research Center, NFRDI were used in the experiments. The experiment was conducted for 12 weeks from 21 August 2013. Fish received intramuscular injection of AI at 5 mg/g BW dose in three times every 3 weeks. Fish were sampled pituitary and gonads at 3, 6, 12 weeks post-injection (n=50). The mRNA levels of FSH-β, LH-β in pituitary and AR, ERα mRNA in gonad were evaluated using qRT-PCR and qPCR. The histological change of gonads observed on light microscope. The gonads of control group contained most perinucleolus oocyte. At 3 to 6 weeks post-injection, the gonads of AI-treated group contained a few degenerated oocytes, spermatogonia and spermatocytes. At 12 weeks post-injection, gonads contained spermatids undergoing spermatogenesis. From 6 to 12 weeks post-injection, the expression level of GtHs subunits mRNA in pituitary was significantly higher than control group. The expression level of AR mRNA in gonad was higher than control group from 3 to 12 weeks post-injection. The expression level of ERα mRNA in gonad was lower than control group from 6 to 12 weeks post-injection. These results suggest that immature longtooth grouper with AI treatment induced masculinization via change of GtH subunits in pituitary, AR and ERα mRNA in gonad.

To effects of sex maturation in olive flounder by regulating long photoperiod, gonadal development and GTH mRNA expression in the pituitary were investigated. Photoperiod was treated natural photoperiod and long photoperiod (15L:9D) conditions from September 2011 to March 2012. The results showed that natural photoperiodic group showed a higher gonadosomatic index (GSI) than long photoperiodic group during the spawning season (March 2012). The histological analysis of ovarian tissue showed that natural photoperiod group of ovaries contained vitellogenic oocytes, but long photoperiod group of ovaries mainly contained perinucleolus staged oocyte and oil-drop staged oocytes. The FSH mRNA of olive flounder, under natural photoperiod group, showed a significantly higher expression but no significant difference under long photoperiod group. The LHβ mRNA showed a significantly higher expression only under natural photoperiod group. These results may suggest that long photoperiodic information regulates secretion of pituitary FSH and LH and maintain early growing stage of gonadal development in this species.