Kotaro Kikuchi

Use of defatted soybean meal as a substitute for fish meal in diets of Japanese flounder (Paralichthys olivaceus)

Feeding experiments were conducted to examine the potential use of defatted soybean meal (SBM) in combinations with blood meal (BM), corn gluten meal (CGM), and freeze-dried meat of blue mussel as a partial replacement of fish meal in the diet of Japanese flounder. Juvenile fish of about 5 g in initial body weight were fed diets to satiation twice daily, 6 days per week for 8 weeks at 20°C. The control diet contained 75% fish meal as the protein source, while 35 or 45% fish meal was replaced with other sources of protein in the experimental diets (replacing approximately 45 or 55% of fish meal protein in the control); 25, 30, or 40% SBM, 10% BM or CGM, and 5% freeze-dried meat of blue mussel. Diets containing 25% SBM in combination with BM or CGM and the blue mussel (replace 47 or 44% of fish meal protein) resulted in best growth and feed utilization among all dietary groups tested. The final body weight, weight gain, and protein efficiency ratio in these dietary groups were higher than those for the control (P<0.05). The weight gain of fish fed diets containing 40% SBM (replace 43%), and 30% SBM in combination with 10% BM or CGM (replace 47 or 45%), were comparable to that of the control, however, feed efficiency and protein efficiency ratio were significantly lower except that feed efficiency for the 30% SBM and 10% BM diet (P<0.05). Diets containing 40% SBM and 10% BM or CGM (replace 59 or 57%) showed inferior growth and feed utilization compared to the control (P<0.05). There were no marked differences in hematological characteristics together with proximate composition of the whole body of cultured fish fed the dietary treatments. These results indicate that about 45% of fish meal protein can be replaced with SBM in combination with other protein sources in the diet of juvenile Japanese flounder.

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.

Japanese Flounder Paralichthys olivaceus

Fish production with closed recirculation systems, which makes reduced discharge of organic and inorganic wastes possible, is considered to be one of the promising approaches for sustainable development of aquaculture. We conducted research on the closed production of Japanese flounder Paralichthys olivaceus since 1986 and obtained information to develop closed aquaculture systems for the flounder such as nitrogenous excretion rate of fish and nitrification activity of marine biological filters for designing water treatment unit, optimum water temperature for the growth, proper stocking density and effects of water quality changes on the growth of fish for increasing production performance, and effective feed composition. Based on the experimental results as well as available knowledge, a pilot scale closed recirculation system of 10 m3 in total water volume was developed with operation manuals specific for Japanese flounder. The system consisted of a culture tank of 4 m in diameter, settling tank, drum screen filter, submerged biological filter, heating-cooling unit, oxygen generator and supplier, blower, and UV sterilizer. In the feeding experiment, 1015 fish of 2 g initial body weight were introduced to the culture tank and fed commercial pellet diet twice daily to satiation each. Fish grew to 456 g after 259 days with good survival rate (85%) and feed efficiency (97%). Culture density at the end was 31 kg/m2; the bottom area of the culture tank and total culture water used was 25m3. Dissolved oxygen ranged from 90 to 130% of saturation through the rearing period. Ammonia and nitrite were maintained at less than 4 mg-N/L, and no apparent adverse effects on the feeding and growth were observed.

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.

Present Status of Research and Production of Japanese Flounder, Paralichthys olivaceus, in Japan

ABSTRACT Aquaculture of Japanese flounder, Paralichthys olivaceus, started in the middle 1970s in Japan, and the commercial production became extensive in the early 1980s, with development of seedling production and farming techniques. Annual production in 1996 was 7,692 metric tons, ranked fourth among marine cultured finfish after yellow-tail, red sea bream, and coho salmon. Marine finfish aquaculture in Japan is mostly conducted in floating net cages; however, land-based culture tanks are the prevalent culture system for Japanese flounder. The tanks are circular, square, or octagonal and constructed of various materials: concrete, plastic and/or a combination of the two. Culture tanks are generally inside or covered with shade cloths. Sand-filtered sea water is continually supplied to each tank, with 12 to 24 exchanges daily. Three-gram fish are stocked in the culture tank and raised for 1 to 2 years until they grow to 500-1,000 g. Survival ranges from 60 to 80%. Sardines and sand lance, fresh or frozen, are mainly fed; however, use of moist or dry pellets are increasing recently because of the decline in catch of these fishes. Fingerlings are obtained from commercial hatcheries virtually year-round. The fish utilize almost no dietary carbohydrate as an energy source, and an increase of lipid in the diet did not improve the growth, although it did seem to produce a slight increase in protein efficiency ratio. Therefore, diet for Japanese flounder should contain high percentages of protein (fish meal). Finding alternative protein sources for fish meal in the diet has been researched, and the potential of defatted soybean, corn gluten, feather, meat, and meat bone meals have been examined. The optimum temperature for the growth is 20-25°C. Salinity range of 4.4 to 34.0 ppt did not affect the growth of Japanese flounder at 8 g initial body weight.

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.