강도다리 Platichthys stellatus의 무안측 흑화발현에 관한 환경생리학적 연구

Abstract

Morphological characteristics for the blind-side hypermelanosis Starry flounder Platichthys stellatus like all flatfish, exhibits conspicuous lateral asymmetry in numerous traits, including the migration of one eye to the other side of the head during metamorphosis. Additional changes related to eye migration include asymmetrical pigmentation, and a behavioral shift from larvae that exhibit upright, open-water swimming to juveniles and adults that lie on the ocean floor, eye side up. While, the morphological characteristic of the juveniles has been quite plastic in recent years, a phenomenon which is thought to be related to a diverse suite of semi-intensive and intensive larviculture methods. The cause of morphological abnormalities in the farmed flatfish is poorly understood. The present study, we observed the features of morphological specificity and abnormality of immature fish (mean total length 23 cm) and survey the occurrence frequency of the specificity and abnormality of juvenile (mean total length 6.7 cm) in artificial culture facility. We found two types of abnormality (e.g., albino in the ocular side and hypermelanosis in the blind side) and a specific lateral polymorphism. These considerably differ from normal individuals (has sinistral eye and pigmented on only one side) by several characteristics including ocular side albinism, blind-side hypermelanosis. The incidence ratio of hypermelanic fish and ratio of pigmented blind area are 91.7±1.7% and 17.4±1.3% respectively. These suggest that these morphometric and morphological differences occur more in artificial environment during and just after metamorphosis.

Physiochemical comparison between normal and abnormal pigmentation on the blind side of starry flounders Experiments were carried out to clarify a physiochemical difference between hypermelanic fish and not hypermelanic fish on the blind side in flounders. The experimental animals of 26.7±1.8 cm in total length and 482.7±102.0 g in body weight were used to analyse AST (aspartate aminotransferase), CPK (creatine phosphokinase), ALB (albumin), IP(inorganic phosphorus), HDLC (HDL cholesterol), Na+ (sodium), K+ (potassium), Cl- (chloride), GLU (glucose), total protein (TP), cortisol in plasma. As a result, GLU and TP were no difference. AST and ALB were higher in the non-pigmented flounders than in pigmented flounders. No difference was observed in CPK, IP, HDLC, Na, K ,Cl, GLU and TP between two groups. but Cortisol level was higher in the hypermelanosis than in the normal. Therefore, it is implicated that the blind-side hypermelanosis of the hypermelanic starry flounder could be related closely with a stress.

Effect of illumination on the blind-side hypermelanosis In order to study the effect of tank color and illumination on feeding, growth and blind-side hypermelanosis of starry flounder Platichthys stellatus, we performed a series of background color and illumination intensity test for 180 days. The test was done in duplicate at 100 fish/tank (430% of initial covering area [PCA]) with the selected normal juvenile flounder (TL 17.3±0.5 cm, BW 82.5±0.2 g). The rearing was performed in dark green FRP aquarium tanks (H100 cm×L100 cm×W100 cm; bottom area 1 m2) lighten with average 230 lux and 1,100 lux, and in white FRP aquarium tank (H100 cm×L100 cm×W100 cm; bottom area 1 m2) lighten with average 230 lux light intensity. We investigated correlation of daily food intake (DFI) with water temperature and salinity, and compared the influences of background colors and light intensity in DFI, food efficiency (FE), growth, survival rate, and ratio of pigmented blind side area and hypermelanic fish ratio. In background and illumination test, DFI, FE and survival rate showed no difference among three groups. The ratios of pigmented area and hypermelanic fish were also not significantly different among three groups, indicating that the blind side hypermelanosis of starry may be governed not by background color (or light intensity) but by a genetics external trait inherited from parents.

Effect of stocking density on the blind-side hypermelanosis To examine the influences of stocking density on feeding, growth and blind-side hypermelanosis of the starry flounder Platichthys stellatus, we performed an experiment with juvenile at two densities: 100 and 400 fish/80 L. The juveniles had a total length of 3.2±0.1 cm, body weight 0.6±0.1 g, and pigmented patches (pigmented ratio 2.6±0.4%) on the blind side. Duplicate experiments were conducted in 80 L glass tanks for 120 days. We determined daily food intake (DFI), food efficiency (FE), growth, survival rate, rate of hypermelanic fish, and pigmented area rate on the blind side at 60 day intervals. DFI and growth were significantly higher at 100 fish/80 L than at 400 fish/80 L. There was no difference in the pigmented area rate between the two density groups. Although the hypermelanosis was not correlated with body size, the hypermelanosis increased with growth. These results suggest that a high stocking density is not the main cause of blind-side hypermelanosis, although it can accelerate hypermelanosis in the starry flounder.

Effect of substratum and background color on the blind-side hypermelanosis To study the influence of background color and substratum on appetite, growth and hypermelanosis of flatfish, we compared the daily food intake (DFI), the feed efficiency (FE), the survival, the growth, the ratio of pigmented area on the blind side and the ratio of hypermelanic fish duplicately reared for 180 days in dark-green FRP aquarium (control), white FRP aquarium together with dark-green substratum. The ratio of pigmented area on the blind side was significantly higher at the dark-green group than at the white group. DFI, FE and growth were higher in the dark-green substratum. Pigmented area rate and ratio of hypermelanic fish were significantly higher at the dark green group than at the high dark-green substratum. The results suggest that bright tank color and substratum bottom could inhibit the hypermelanosis.