Nakahiro Iwata

Effects of sandy substrate and light on hypermelanosis of the blind side in cultured japanese flounder Paralichthys olivaceus

Rearing experiments were carried out to clarify the effects of sandy substrate and light irradiation on hypermelanosis of the blind side (the staining type of ambicoloration) in cultured Japanese flounder. Fish were reared in three experimental conditions: (1) no sandy substrate into which fish could bury themselves and with upward light irradiating their blind sides, (2) no sandy substrate and no upward light, and (3) sandy substrate (transparent glass sand) with upward light irradiation. Pigmented areas on the blind side were measured by an image analyzing system. Flounder from the third condition (sandy substrate with light irradiation) showed the lowest pigmentation on the blind side. In contrast, fish from the second condition (no sandy substrate and no light irradiation), showed the highest pigmentation coverage. These results indicate that sandy substrate on the bottom in culture tanks is more important than light irradiation as a factor affecting hypermelanosis of the blind side in cultured Japanese flounder.

Growth of tiger puffer Takifugu rubripes in closed recirculating culture system

Two feeding experiments were conducted to elucidate growth performance of tiger puffer in a 10 m3 water volume closed system. In experiment 1, 1000 fish of 3.5 g average body weight were fed tiger puffer commercial feed twice daily to apparent satiation, 6 days a week for 224 days. Sand-filtered sea water was used and no water was exchanged during the rearing period. Immediately after cutting of lower teeth at day 112, daily feed consumption decreased greatly and 60 fish died in few days. Feeding rates recovered and then decreased gradually as nitrate levels increased from 600–1048 mg N/L. Fish grew to 343 g with 91% survival rate and 87% feed efficiency. Rearing conditions of experiment 2 were similar to experiment 1, except that culture water was exchanged to maintain the nitrate level less than 600 mg N/L during the 224-day experiment. Mortality and reduction of feed consumption occurred immediately after teeth cutting as was observed in experiment 1. Significant reduction of feed intake was not found during other rearing periods. Fish of 3 g grew to 303 g with 91% survival rate and 72% feed efficiency.

Effects of copper on survival and growth of larval false clown anemonefish Amphiprion ocellaris

Larval false clown anemonefish of about 12h after hatching were fed newly-hatched brine shrimp nauplii in natural (control) and copper-added seawater (40–640 μg-Cu/L) at 26.5±0.5°C for 14 days. Survival rate of the fish increased with increasing copper concentrations up to 160 μg-Cu/L. The rates at 80 and 160 μg-Cu/L were 65 and 80%, respectively, and were significantly higher than that of the control (30%). A positive effect of copper addition on the survival rate was also observed in the other rearing experiment with the fish from seven different spawning chances. Growth rate of the survival fish was not affected by copper concentrations. The copper concentration of the survived fish increased with increasing copper concentrations in the rearing water.

Effects of fish size and water temperature on the acute toxicity of boron to Japanese flounder Paralichthys olivaceus and red sea bream Pagrus major

The acute toxicities of boron were examined for Japanese flounder Paralichthys olivaceus and red sea bream Pagrus major in terms of fish size and water temperature. Japanese flounder of 0.1–70.0 g and red sea bream of 0.6–20.3 g were exposed to different concentrations of boron for 96 h at 20°C under semi-static conditions. In both fish species, the median lethal concentration (LC50) for 96 h of boron increased linearly with increasing fish size, ranging from 108 to 252 mg B/L for the flounder, and from 97 to 172 mg B/L for the sea bream. The effect of water temperature on acute toxicity was examined for Japanese flounder of 0.6 and 1.5 g at 10, 15, 20 and 25°C, and for red sea bream of 0.6 and 2.4 g at 12, 15, 20 and 25°C. The toxicity of boron for the flounder increased linearly with increasing water temperature. The 96 h LC50 values ranged from 299 to 108 mg B/L for the 0.6 g flounder and from 350 to 113 mg B/L for the 1.5 g flounder. A similar trend was shown for the 2.4 g red sea bream; however, the relationship for the 0.6 g red sea bream was not significant.