Marble goby Oxyeleotris marmoratus is an important aquaculture freshwater (FW) species in Southeast Asia. To improve hatching technique, eggs from a river population in Sabah, Malaysia were incubated in FW and seawater (SW) diluted to 5, 10, 15, 20 and 30 psu, comparing hatching rates and larval deformation. Egg development, hatching rates, hatching periods, larval deformation and survival at 10 days after fertilization (dAF) were then compared in FW and 10 psu SW. Salinities from FW to 15 psu SW were tolerated, with the highest hatching observed at 10 psu SW (60.0±2.0%, mean±SD). Significantly higher hatching rates and lower deformation rates were observed at 10 psu SW than in FW. In FW, embryonic developed at similar rate with 10 psu SW, but hatching was delayed and all larvae died by 10 dAF. Peak of hatching in 10 psu SW observed in 48-60 hours after fertilization (hAF) (33.1±5.6%) while hatching in FW was delayed and peaked 72-84 hAF (10.6±3.4%). Larvae that hatched later had higher deformation rates. The eggs incubated in 10 psu SW had a shorter hatching period, higher hatching rate and better larval survival than those in FW.

View full abstract

The expansion mechanism of the stomach in the puffer fish Takifugu rubripes was examined by recording the water pressure in both buccal and opercular cavities, differential pressure between buccal and opercular cavities, and water volume inhaled and exhaled into/from the mouth, and by observing the flow of water into/from the stomach with Evance blue solution poured into the opercular cavity. The expansion and the shrink of the stomach were analyzed with 8 phases presumed from the records and the observations, applying the model of fish gill ventilation. These results revealed that the stomach of the puffer fish expands and shrinks using the water pressures of the buccal and opercular cavities, the differential pressure, and opening and closing movements of the buccal and the opercular valves and the gullet sphincter.

View full abstract

Biwa salmon Oncorhynchus masou rhodurus endemic to Lake Biwa is among the tastiest fishes, and its aquaculture is gaining increasing expectations. We fed large maturing Biwa salmon (initial mean body weight 283 g) with either a low-phosphorus (P) fish meal-free diet (LP; P=0.71%) or a commercial diet (Cm; P=1.68%) for three months in six 1-ton tanks. Final mean body weight of fish was 370 g (LP) and 392 g (Cm). Male fish, but not females, fed the LP diet had lower bone ash and P contents than normal. Fillet fat content was 9.5% (LP) and 7.9% (Cm). Fillet eicosapentaenoic and docosahexaenoic acids contents were also higher for the LP than Cm fish. Organoleptic scores of fillets were higher for the LP than Cm fish. Effluent soluble P was -0μg/l (LP) and 118μg/l (Cm). Absorption of dietary P was 50.8% (LP) and 28.8% (Cm), while fecal P excretion per kg of feed consumed was 3.5 g (LP) and 12.0 g (Cm). When the LP diet was supplemented with phytase, the fecal P decreased further by -30%. Thus, the LP diet could be a feasible alternative to traditional fishmeal-based diets in environmentally conscious Biwa salmon aquaculture.

View full abstract

Changes of the ventilation volume and the amount of oxygen uptake with feeding Chaetoceros gracilis were examined in the rock-oyster Crassostrea nippona. At a density of 20,000 cells/ml, the ventilation volumes at 17, 20, 25 and 28°C increased to 9.2, 8.1, 6.6 and 3.8 times (8.60, 10.88, 13.00 and 9.30 l/min/kgWW, per wet weight of soft part of body) those without feeding (0.93, 1.35, 1.98 and 2.46 l/min/kgWW), respectively. The amount of oxygen uptakes with feeding at 17 and 28°C were 0.580 and 0.910 ml/min/kgWW and were about equivalent to those, 494 and 0.880 ml/min/kgWW, without feeding, respectively. However, the amount of oxygen uptakes increased to 1.6 and 1.5 times (0.769 and 1.040 ml/min/kgWW) those without feeding (0.485 and 0.710 ml/min/kgWW) at 20 and 25°C, respectively. These results suggested that the Rock-oyster increased the ventilation volume without a marked increase in the amount of oxygen uptake with feeding.

View full abstract

High- and low-virulence serotypes of the fish pathogen Vibrio anguillarum were challenged with a beneficial bacterium (Sulfitobacter sp. RO3) in the presence of the phytoplankton Nannochloropsis oculata. The inhibitory activity of Sulfitobacter sp. against these V. anguillarum serotypes were observed in (1) phytoplankton culturing control medium (ESM) and (2) NCF, a filtrate prepared from N. oculata cultured in ESM. The presence of Sulfitobacter sp. in ESM significantly reduced the number of viable cells of all V. anguillarum serotypes tested (O2, O3, O4, O9 and O10). In NCF, Sulfitobacter sp. totally eradicated the O2 and O3 serotypes. The viabilities of the low-virulence serotypes O4, O9 and O10 when cultured in NCF in the presence of Sulfitobacter sp. were not significantly different from those cultured in ESM. We conclude, therefore, that phytoplankton cultured in the presence of naturally occurring Sulfitobacter sp. provide an essential tool for inhibiting the growth of the economically significant high-virulence fish pathogen V. anguillarum.

View full abstract

The amount of oxygen uptake (Vo₂) and ciliary movement (CM) were measured in the Japanese short-neck clam Ruditapes philippinarum with a rise in water temperature at a rate of 3°C/hr from the seasonal temperature: 10°C (January), 16°C (March), 22°C (June) and 28°C (August). The Vo₂ values in the clam acclimated to seasonal temperatures of 10, 16, and 22°C increased with a rise in temperature, and the Vo₂ values to 28°C decreased. The Vo₂ values in the clam acclimated to seasonal temperatures of 16 and 22°C were approximately equivalent to those in the clam rose to 6°C higher than the seasonal temperatures of 10 and 16°C, respectively. However, the Vo₂ value in the clam acclimated to a seasonal temperature of 28°C was lower than that in the clam rose to 6°C higher than the seasonal temperature of 22°C. The CM in the clam acclimated to seasonal temperatures of 16, 22, and 28°Cwas approximately equivalent to those in the clam rose to 6°C higher than the seasonal temperatures of 10, 16, and 22°C, respectively.

View full abstract

We investigated biomass and taxonomic composition of protist plankton in the Yakugachi River of Amami-oshima Island during winter, to evaluate food availability for the larvae of Plecoglossus altivelis ryukyuensis. No significant difference was found for total biomass of microbial plankton community among the stations, and diatoms composed more than half of the biomass. Biomass of dinoflagellates and naked ciliates was higher at the estuary stations compared with that at the upstream station. Calculating carrying capacity for the larvae egg-hatched after 5 days, biomass of dinoflagellate and naked ciliates at the estuary stations could support the respiratory requirements of more than 15×10³ animals/m³/day. These results suggest that biomasses of dinoflagellates and naked ciliates in the estuary of the Yakugachi River are enough for survival of the larvae.

View full abstract

Taurine supplementation, to compensate for the reduction of fish meal (FM) in fish diets, has been the subject of numerous investigations. However, the taurine contents of FM-based diets are still lower than in diets of raw fish, even in diets where FM is the only protein source. In this study, the effect of taurine supplementation to commercial feed (containing 57% FM) on skin thickness and scale detachability in red sea bream Pagrus major was investigated. Three different levels of taurine were used: 0% taurine (control), 1% taurine (Tau-1%), and 2% taurine (Tau-2%). Red sea bream (average body weight, 107 g) were fed these diets for 60 days. No effects of taurine supplementation on growth and feeding efficiency were observed. However, skin thicknesses of fish from the Tau-1% and Tau-2% groups were significantly higher than for the control group, and scale detachability of the control group was significantly higher than for the Tau-1% and Tau-2% groups. These results suggested that taurine supplementation of commercial feed contributes little to growth performance, but does improve skin condition, in red sea bream.

View full abstract

About 187,000 juvenile hatchery-reared black rockfish Sebastes schlegelii were marked and released in Miyako Bay of Iwate Prefecture each summer during 1999-2001. The total lengths and fished sites of all recaptured S. schlegelii at the Miyako fish market were surveyed through 2005. Among all recaptured S. schlegelii, 1-, 2-, and 3-year-old fish respectively accounted for 88.5%, 10.0%, and 1.5%. Additionally, 91.8% of the 1-year-old recaptured fish were landed during August-December. The average total lengths were 18.0-21.3 cm in August and 21.1-24.8 cm in December of each year. Furthermore, the released fish were recaptured mainly by set nets in the innermost area of the bay during August, although the number of fish recaptured by set nets increased in central and mouth areas from September. These results suggest that 5-10 cm S. schlegelii juveniles released into Miyako Bay stay within the innermost nursery area for a year. Subsequently, they start to migrate from the shallow area to the deep bay mouth area around August the following year.

View full abstract

This paper describes the occurrence, migration period and vertical distribution of whitespotted conger (Conger myriaster) leptocephali in the northeastern Harima Nada Sea, part of the eastern Seto Inland Sea, Japan as fundamental information for fishery stock management of the species. In 2003 to 2009, a small midwater beam trawl net with a 2.4 mm mesh aperture of a codend was towed with a small boat (9.1 mt) in the three (surface, middle and bottom) layers of the study area (20-25 m in depth) from January to May. The leptocephali migrated to the sea from February to May (mainly from March to April) when sea surface temperature measured 8-18°C. They occurred in the bottom and middle layers (mainly in the bottom layer) in the daytime, but they spread to the surface layer at night. A half of them migrating to the sea were at the metamorphosing stage, which implies that many of the leptocephali move to the northeastern Harima Nada Sea with metamorphosing.

View full abstract

Characteristics of ayu Plecoglossus altivelis altivelis, fishery by several methods during daytime in the Jinzu and Shou rivers was investigated from 2002 to 2004. Fishing methods of angling by decoy and sinking - fly, licenses unlimited in number and those of cast gill net, cast net and angling on bottom, licenses limited in number were used in each fishing ground. Anglers using decoy accounted for most of the fishermen in the Jinzu River where many fishermen were counted, and they showed higher fishing effort than those of limited licenses such as cast net. Numbers of fishermen using decoy, sinking - fly, cast gill net and angling on bottom deceased with increased water flow, and no fishermen was observed in more than a certain water flow. On the other hand, that of cast net remained at a high level in the case that water flow increased. The reason why many fishermen visited the Jinzu River was due to the high water flow and good conditions, and it is considered in order to increase fishermen angling the Shou River, it is necessary to increase water flow or make the special area for anglers using decoy.

View full abstract

We investigated the genetic population structure of amago salmon Oncorhynchus masou ishikawae in the Nahari River system, Kochi Prefecture, Japan, using mitochondrial DNA and microsatellite DNA. We collected 132 individuals from four populations in three tributaries of the Nahari River. Of these, two populations from the upper sections of two tributaries where there have been no official records of stocking activity were genetically isolated from the other populations by erosion-control dams. These two populations were identified as distinct native populations with low genetic diversity. A conservation program may be required to avoid their extinction. The lower section of one of these tributaries has been stocked annually. We found no evidence of interbreeding between fish from the upper section and the released hatchery fish. The third tributary has no artificial dams or similar constructions and genetic introgression from hatchery fish into the wild population was revealed. Our results may be used to direct conservation program for the native amago salmon in the Nahari River system.

View full abstract

To elucidate the feeding and growth of larval greater amberjack Seriola dumerili with non-inflated, normal inflated and over-inflated swim bladders, we measured the total length, swim bladder volume and number of rotifers in the gut of larvae reared in small tanks of 500 l volume and large tanks of 80 kl volume. Anesthetize larvae with inflated swim bladders were introduced into the beaker containing the seawater (25°C; mean specific gravity, 1.0266); then, larvae surfaced (floating larvae) and those sunk or showed neutral buoyancy (larvae with normal inflated swim bladders) in the beaker was separated. Proportion of larvae with inflated swim bladders showed ~70-100%. Floating larvae were detected from 6-7 days after hatching in both small and large tanks, and their proportion to the total number of larvae with inflated swim bladders reached ~40% on average in large tanks. Swim bladder volume of floating larvae was significantly larger than that of larvae with normal inflated swim bladders, i.e., floating larvae had over-inflated swim bladders. Feeding and growth of larvae with non-inflated and over-inflated swim bladders was inferior to those of larvae with normal inflated swim bladders.

View full abstract

Morphological characteristics of fixed phagocytes (FP) in the antennal gland of kuruma prawn Marsupenaeus japonicus were examined by electron microscopy. Four types of FP (type 1-4) were observed in this gland. Type 1 FP was located on the basal membrane of the gland tubule and phagocytosed foreign substances such as colloidal carbon and latex beads injected into abdominal muscle of the prawn. Electron-dense materials which considered as residual body (RB) after phagocytosis were also observed in the type 1 FP. Type 2, 3 and 4 FP did not phagocytose foreign substances described above. However, RB or phagosome was observed in these types of FP. Type 2 FP was situated in the fibrous area between the gland tubule and the coelomosac, therefore, this FP may be mesangial cell. Podocytes (type 3 FP) in the coelomosac of the gland contained various materials in the large vacuoles. Type 4 FP with many fine granules was observed in the lumen of the antennal gland tubule.

View full abstract

We investigated the acid-base balance of the pearl oyster Pinctada fucata martensii under normoxic conditions by measuring the pH, total CO₂ content (Tco₂), O₂ partial pressure (Po₂), CO₂ partial pressure (Pco₂) and bicarbonate concentration ([HCO₃^-]) of the hemolymph collected from the adductor muscle (HAM). The Pco₂ and [HCO₃^-] were calculated by using Henderson-Hasselbalch equation that substituted the values of the apparent dissociation constant of carbonic acid (pK) determined in this study. The hemolymph pH, Tco₂, Pco₂ and [HCO₃^-] were 7.284-7.330, 1.90-2.10 mM, 2.08-2.10 mmHg and 1.83-2.04 mM, respectively. The pH, Tco₂, Pco₂ and [HCO₃^-] of the hemolymph collected from the anterior aorta (HAA) were 7.284-7.375, 1.77-2.10 mM, 1.79-2.33 mmHg and 1.72-2.00 mM, respectively. The pH, Tco₂, Pco₂ and [HCO₃^-] in both HAM and HAA sampled repeatedly every one hour did not show any significant difference. There were no significant difference between HAM and HAA in terms of pH, Tco₂, Pco₂ and [HCO₃^-]. The non-bicarbonate buffer values and pK of the HAM were similar to those of HAA.

View full abstract

A study was conducted to determine the interactive effects of vitamin C (VC, AsA) and E (VE, α-Toc) supplementation with dietary oxidized fish oil (OFO) on tissues α-Toc and AsA concentrations and reduction of oxidative stress of red sea bream. A 21-days feeding trial on red sea bream (average weight 28.9±0.1 g) was reared in sixteen tanks (200 l, 6 fish per tank, in duplicate), and fed with eight test diets containing two degree of fish oil (8.9 meq/kg and 156.9 meq/kg) with varying levels of AsA (500 and 1,000 mg AsA equivalents/kg diet) and α-Toc (100 and 200 mg α-Toc equivalents/kg diet) supplementation, respectively. No difference (P>0.05) on growth performance was observed. Increasing dietary AsA and α-Toc concentrations significantly increased liver α-Toc and AsA concentrations, respectively. Fish fed dietary OFO with supplemental 500 mg/kg of AsA and 200 mg/kg of α-Toc showed higher (P>0.05) oxidative stress condition. However, supplementation of α-Toc (200 mg/kg) or/and AsA (1,000 mg/kg) improved health condition of fish. In conclusion, we suggested that higher concentrations of AsA and α-Toc in diets may reduce oxidative stress levels, supplement of 1,000 mg/kg diet could be needed to maintain health condition of red sea bream.

View full abstract

We examined new external marking methods for swimming crab by removing or incising the abdominal segment using micro scissors. The 6 and 7th abdominal segments were removed from crabs of about 10 mm in total carapace width and for crabs of about 30 mm in total carapace width incised longitudinally from the tip of the tail to the middle of the 6th abdominal segment. Most of crabs exhibited no recovery of the 7th abdominal segment after removal. When a few crabs recovered them, the recovered portion was bent. The 7th abdominal segment was cleaved into two pieces, or the tip of the 7th abdominal segment was split by the incision method. The deformity was formed within a few molts and subsequently remained over 450 days. In addition, we observed no similar deformity in wild crabs. These results suggest that these marking methods are suitable for practical use for mark-recapture surveys for swimming crab. We expect that the incision method is particularly effective, because this method showed no significant difference in survival rates between marked crabs and control crabs.

View full abstract

This study was performed to investigate the beneficial use of yuzu pomace as a feed additive in young yellowtail. The antioxidant effects of grated yuzu rind from pomace (yuzu paste) in the prevention of dark muscle discoloration during storage of sliced young yellowtail were tested. Dark muscle discoloration during storage at 4°C was significantly reduced in fish fed a yuzu paste-supplemented diet (50 g yuzu paste in 1,450 g of diet, wet basis). This result indicates that the supplementation of yuzu paste to diets is effective to prevent dark muscle discoloration in young yellowtail.

View full abstract

Antimicrobial activity against water mold disease during artificial breeding of rosy bittering Rhodeus ocallatus by the schales method was investigated using solutions: 0.1% saline, 0.5% saline and 0.0001% methylene blue. The growth of Oomycota was inhibited by all three solutions. The highest survival rate was recorded in the case with methylene blue solution. However, the saline solutions did not contribute to the improvement of the survival rate. These results showed that the sterilization with the methylene blue solution was effective for controlling water mold disease infection.

View full abstract

The number of pectoral fin rays (PFRs) in the juvenile masu salmon Oncorhynchus masou masou on the Sea of Japan side of Hokkaido Island was analyzed to determine geographical variation. Thirteen populations were collected and PFRs were counted. A significant latitudinal cline was observed. The number of PFR was higher in southern rivers than in northern rivers.

View full abstract

The influence of seagrass vegetation of Zostera marina on the sediment meiofauna was investigated by making a faunal comparison between vegetated and unvegetated areas in the subtidal zone in the middle of Tanoura Bay, Shizuoka Prefecture. The vegetation and season did not affect the number of taxa. The meiofaunal diversity was not influenced by vegetation but by season. The abundances of Copepoda, Malacostraca, Oligochaeta and Ostracoda were influenced by season. On the other hand, the abundance of Nematoda was influenced by area as well as season. Consequently, Nematoda is considered to be an indicator for investigating the impact of seagrass vegetation on the sediment meiofauna in the middle of Tanoura Bay.

View full abstract

Morphological change of hemocytes with cytoplasmic deposits of kuruma prawn Marsupenaeus japonicus were examined by electron microscopy. The hemocytes were not hyaline cell, but granulocytes. The granules of the granulocytes were exocytosed (degranulated) in vitro. Previous investigators reported the hemocyte type as hyaline cell. They would observe the degranulated granulocytes. Some granulocytes without cytoplasmic deposits also showed degranulation.

View full abstract

To determine the temperature conditions inducing deformity of inter-nostril epidermis in the mass seedlings of red sea bream at high frequency for use as an external marker in stocking surveys for enhancement, we conducted the rearing experiments in the hatchery for mass seedlings. After the temperatures of all three intensive rearing experiments were kept at 20°C from hatching to (ca.) 5 mm (total length), their three temperatures were increased slowly from 5 mm to 8 mm. Then we kept them at 21°C, 23°C and 25°C, respectively, in mean until after 40 days after hatching. Another temperature of one rearing experiment was natural condition (23°C) in the relatively extensive experimental pond for mass seedlings. We inferred the possibility of producing a percentage of ca. 80-90% of deformed inter-nostril epidermis of mass-seedlings by controlling the temperature at 20-21°C from 0-36 days after hatching. In contrast, the percentages of deformed inter-nostril epidermis on the other higher temperatures were ca. 1-35%. Because our experiments were relative higher temperatures, it is also important to note some morphological abnormalities except deformed inter-nostril epidermis.

View full abstract