Three methods ofEnteromorpha proliferaseeding, for commercial cultivation, were compared at the seaweed cultivation grounds in Yosino River, Tokusima Prefecture. The three methods were “natural”, “direct” and “artificial”. E. proliferafronds grew well on culture nets seeded by any of the methods applied; daily growth rates were between 20-40 %, with a maximum of 73.4 % during the test period. Plants only attained harvestable size when the nets were held at depths of 30-90 cm.

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This paper reports on a novel method of artificial seeding of the green algaEnteromorpha prolifera. Fronds of E. proliferawere chopped up in a rotary blender, the tissue then released large numbers of spores, for several days, once transferred to seeding tanks containing culture nets. This new method of production was used to seed nets twice during the year, viz. March-April and September-November; thereafter the culture nets with attached spores were transferred to the nursery grounds. Juveniles of E. proliferagrew well during the nursery phase when subjected to a 2 hourly daily cycle of drying.

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The tolerance ofCorbicula japonicato low concentrations of dissolved oxygen (DO) was examined in laboratory experiments using individuals collected from Lake Shinji, Japan. Tolerance varied with water temperature. In anoxic conditions, C. japonicasurvived for more than 17 days at 10°C and 20°C, while all individuals at 30°C died with in 10 days. The tolerance to anoxia seemed no difference between juveniles and adults. Oxygen consumption of C. japonicawas higher at 30°C than 20°C. Even after conditions became anoxic due to respiration, all individuals maintained at 20°C survived more than 50 days. Individuals maintained at 30°C, however, died with in 8 days. The minimum oxygen requirement at 28°C with in a 30-day period was between 1.0 mg/l and 1.5 mg/l.

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Sulfide tolerance in the bivalve Corbicula japonica was determined based on laboratory experiments using individuals collected from Lake Shinji, an estuarine lagoon in Japan. The median tolerance time (LT₅₀) of individuals immersed in a 50 mg/l sulfide solution at 18°C was 23 days, while the LT₅₀in 1.0mg/l sulfide solution at 28°C was 21 days. At any given water temperature, the tolerance time decreased as sulfide concentration increased. The sulfide tolerance seemed similar between juvenile and adult C. japonica. C. japonica has a much higher sulfide tolerance than other macrobenthos that was reported at sulfide tolerance, which may reflect the adaptation of C. japonicato brackish environments where salinity stratification commonly causes anoxia and sulfide formation at the bottom.

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Horizontal starch gel electrophoresis was used to analyze the genetical variation between Takatsu River (=stocked) and Lake Jinzai (=wild) populations of Japanese mitten crab Eriocheir japonica. Ten enzymes and 16 allozymic loci were examined using muscle, gill, and hepatopancreas tissues. Six loci, AAT-1, AAT-2, FH-2, GPI, IDHP-1, and MDH-2, were found to be polymorphic. The value of mean heterozygosity was 0.029 for the Takatsu River (=stocked) and 0.027 for Lake Jinzai (=wild) . The difference of allele frequency between these populations was not significant. Nei's genetic distance between these populations was 0.0001.These results suggest that these populations show no genetical difference at the present time.

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Initial feeding traits of larval red snapper Lutjanus argentimaculatus were investigated by supplying nauplii of the calanoid copepod Acartia sinjiensis and rotifers. The gut content of larvae consisted solely of A. sinjiensis nauplii (mean 2.1-7.2 nauplii/larva) on 0-2 days after initial mouth opening (days 0-2) . The mean body width of the nauplii ingested was 0.058 mm on day 0, subsequently increasing with larval age. Feeding on rotifers (mean lorica width, 0.117 mm) was observed from day 3 (mean 0.92 rotifers/larva), with the number ingested increasing markedly on days 4 and 5. The mouth width of red snapper larvae on day 0 (0.166-0.188 mm) was larger than the body width of the nauplii and rotifers but smaller than those of other fish species conventionally reared using only rotifers. This small mouth size may have been initially restrictive, allowing only the seizure of early nauplii at the onset of feeding. The larvae grew well from 2.84 mm in mean total length (TL) on day 0 to 3.38 mm TL on day 5, without significant mortality. Nauplii of A. sinjiensis constitute a promising initial food for early red snapper larvae and very likely also for those of other marine fishes with a small mouth size.

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A deformity consisting of abrupt or steady lateral curvature of the lower lobe of the caudal fin was recognized in artificially produced Ayu, Plecoglossus altivelis, fly. The deformity was related to the current in the rearing tank: a counterclockwise current induced curvature to the left in 6.5 to 23.3% of the fish, whereas a clockwise current induced curvature to the right in 23.3 to 34.5 % of the fish. The deformity rates could be reduced by periodically inverting the current direction and feeding fish with rotifers, Brachionus plicatilis.

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Growth and physiological conditions of diploid and triploid Japanese pearl oyster, Pinctada fucata martensii were compared from May 1995 to January 1996. Food availability, as indicated by phytopigment concentration (chlorophyll-a + pheopigment) in environmental water, was approximately 1.0μg/l and 0.5μg/l from May to September and October to January, respectively. Both types of oysters grew satisfactorily from May to September, but had negligible growth from October to January. About 30 % of the oysters died between October and January. The diameter of pearls did not grow in the period of mortalities. The glycogen content in the adductor muscle and total protein content in the serum decreased in autumn. Moreover, 6-phosphofructokinase activity of diploids decreased from September to November whereas their fructose-1, 6-bisphosphatase activity increased remarkably in November. From these results, it is suggested that the primary cause of Autumn mortality was starvation due to a shortage of food.

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Hepatopancreatic parvo-like virus (HPV) is a kind of virus detected from the epithelial cells of the mucosa of the fore-midgut and those of the hepatopancreas of the Chinese prawn, Penaeus chinensis. In order to verify its pathogenicity, experimental infections were made in healthy larva and adults by the immersion and oral feeding methods, respectively. The results indicated that Z-3, P-7, and adults can all be infected. The mortalities caused by HPV infection were highest in Z-3 followed by P-7 and lowest in adults. These results consistent with mortalities due to HPV in natural pathogenesis. Histopathological changes in the infected prawns were similar to those of naturally infected prawns, which are the occurrence of basophilic or acidophilic inclusion bodies in the nuclei of the epithelial cells of hepatopancreas or in the mucosa of the fore-midgut. Electron microscopic observations showed that there were large numbers of virions, 22-24 nm in diameter, in the virogenic stroma. The above results prove that HPV is a pathogen responsible for the pathological changes in the hepatopancreas and fore-midgut and consequently for the death of Penaeus chinensis.

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The effects of oral administration of estradiol-17β (E₂) to young on gonadal sex and growth of Japanese eel were examined. Juveniles were fed on a diet containing E₂ at a dose of 10 mg/kg diet for various periods after adaptation to the fomulated feed. The female ratio was significantly increased in all E₂-treated groups when compared to the control. The highest female ratio was observed in the group reared for 4 months on the feed containing E₂.
The growth of females treated with E₂ was similiar to that of controls up to about 200g body weight. Thereafter, the growth of female eel treated with E₂ was accerelated when compared to male of control. At the age of about 2.5 years, E₂-treated females had grown to the same size of wild-caught sexually-maturing eels.

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The changes in ovarian development during final oocyte maturation and ovulation induced by different hormonal treatments in cultured tiger puffer Takifugu rubripes were monitored by ovarian biopsy. Single implantation of LHRH-a (des-G1y¹⁰ [D-Ala⁶] -LHRH ethylamide) cholesterol pellet (LHRH-a 400, μg/kg) or osmotic pump (LHRH-a 50 μg/day/fish for 2 weeks) successfully induced ovarian maturation and ovulation in three-year-old cultured tiger puffer with yolk-laden oocytes. Repeated injections of HCG (500 IU/kg) combined with chum salmon pituitary (SP) homogenate (7 mg/kg) every 5 days also induced ovarian maturation and ovulation. Overall, the mean time span from the beginning of hormonal treatment of fish with initial oocyte size between 800 and 900 μm in diameter to ovulation was 18.8 days. In contrast, the mean time span in fish with initial oocyte size over 900μm in diameter was 10.6 days. Oocytes in the control fish receiving no hormones did not develop and became atretic. The results obtained indicate that a single implantation of LHRH-a cholesterol pellet is efficient for inducing maturation and ovulation of cultured tiger puffer. Also, the monitoring of initial oocyte diameter by ovarian biopsy was found to be important for achieving synchronous spawning of several fish.

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Gonadal maturation in hybrids of red sea bream _??_ ×black sea bream_??_and red sea bream_??_×silver bream_??_reared for 4 years in net cages on the sea was compared with that of red sea bream, black sea bream, and gynogenetic diploid silver bream. The gonads of both hybrids were clearly immature in their appearance compared with those of the parent species during the same period. The gonado-somatic index of the three parent species peaked in April with average values highr than 8 whereas the values for hybrids never exceeded 1. Histological examination of the gonads revealed spermatogonia, spermatocytes, spermatids, and spematogenesis in the males of both hybrids, but oocytes were not observed. From these results, it was made clear that both males and females of the two types of hybrids showed hybrid sterility.

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The rates of oxygen consumption and ammonia excretion after feeding of the Japanese flounder Paralichthys olivaceus were measured over a 24-hour period for a group fed once at 09: 00 hours and a group fed once at 18: 00 hours. The specific dynamic action (SDA) magnitudes of the two groups after feeding were not significantly different, but they showed different patterns during the experimental period. The peak level of oxygen consumption for the group fed at 18: 00 hours was 24.5 % higher than that of the group fed at 09: 00 hours. There were no significant differences between either the peak ammonia excretion rate for each group or between the mean ammonia excretion rate for each group. A single peak in ammonia excretion occurred 3-6 hours after feeding for both groups during the 24-hour experimental period. The rate of ammonia excretion returned to the pre-feeding level approximately 24 hours after feeding.

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We compared feeding and growth potential between diploid and triploid rainbow trout Oncorhynchus mykiss under communal and separate rearing conditions. Under communal rearing conditions and at 100 % of the daily feeding rate of dry food recommended by Leitritz, significant differences in the body weight between diploid and triploid were noted from 16 weeks after the start of the feeding trial. At twenty weeks, the mean body weight of diploid and triploid trout were 18.62 ± 0.21 (SEM) and 17.38 ± 0.22 g, respectively. When using 50% or 30% of the feeding amounts recommended by Leitritz, there was a proportional decrease in the growth rate of triploids in comparison with that of diploids as feeding amounts decreased. Under separate rearing conditions and at 100 % feeding rate, triploid showed better growth than diploid. A comparison of the amount of food taken by diploid and triploid trout in communal rearing conditions revealed a progressive decrease in the food available for the triploids with decreased feeding rates. The growth hormone levels in plasma in both ploidies were not significantly different. These results suggest that the decreasing growth rates of triploids reared together with diploids was due to poor performance of the former in the competition for food.

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Effect of starvation on the temperature preference of young horse mackerel Trachurus japonicus was investigated with a vertical temperature gradient. The fish, which had been previously fed to satiation at 25°C, were starved for 56 days. Condition factor of the starved fish decreased from 1.85 to 1.43 during the experiment. The preferred temperatures of the fed and starved groups were 25.3 and 23.0 °C, respectively; no change in preferred temperature was observed during starvation. The thermoregulatoly behavior of starved fish may be effective in sparing the endogenous energy reserves, because the metabolic rate is conceivably less at lower sparing temperatures.

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Changes in chemical content and enzyme activity of red sea bream Pagrus major eggs with high hatching rates (HH) during embryogenesis were compared to the eggs with low hatching rates (LH) . Triacylglycerol contents of both LH and HH showed similar changes and fell linearly during embryogenesis. LH had lower free tyrosine, phospholipid, and phosphocreatine contents than HH between the early cleavage stage and the Kupffer's vesicles appearance stage. No significant differences between HH and LH were found in aspartate aminotransferase, creatine kinase, and alkaline phosphatase activities but LH showed significant lower alanine aminotransferase activity than HH at the embryo appearance stage. These results suggest that free tyrosine and phospholipid contents are possible criteria for estimating egg quality of red sea bream.

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Hatching times (50% hatch) and hatching rates of red sea bream, Pagrus major eggs incubated in 10^-5M single amino acid solutions with artificial seawater were investigated. The eggs were introduced into the culture media at the stage of heart-beat initiation. Hatching times in the media of L-glutamic acid, taurine, L-tryptophan, L-proline and L-cystine were significantly shorter than incontrol artificial seawater. The branched amino acids such as L-valine, L-isoleucine and L-leucine reversely delayed the hatching time as compared with the control. A linear correlation between hatching time (X) and hatching rate (Y) was noted; Y=242.6-147.2X (r=-0.75) . These results suggest that some amino acids can advance hatching time and increase hatching rate of red sea bream eggs, possibly through the promotion of hatching enzyme secretion or the differentiation and formation of organs.

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Two groups of one female and two males of red sea bream Pagrus major broodstock were reared under starvation and feeding during the spontaneous spawning period. Both groups produced eggs almost every day through the spawning period. Regrdless of feeding protocol, the size, crude protein and phospholipid (PL) contents of eggs tended to gradually lower with increase in spawning water temperature, while egg triacylglycerol content remained relatively constant throughout the spawning period. Furthermore, the high egg crude protein and PL contents had an ill effect on the rate of buoyant eggs. These results show that red sea bream broodstock perform normal spawning behavior even under starvation through the spawning period and that egg crrde protein and PL contents have a tendency to reflect egg quality of red sea bream.

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Feeding experiments were conducted for 2 years in commercialscale net cages (10×10×8m) in order to evaluate the dietary value of a newly developed soft-dry pellet (SDP) for juvenile and adult yellowtail.
Three kinds of SDP were prepared from the same ingredients, but slightly varying their contents to produce diets containing 43-47% protein and 18-23% lipid. The diets were offered to three size groups of fish, both in Expt. I (average weights: 32, 38 and 54g) and in Expt. II (average weights: 34, 35 and 44g), from June to October. The fish in Expt. I grew upto 677, 750 and 1020g respectively; the corresponding feed gain ratios being 1.07, 1.08 and 1.19 and the survival rates being 70.2, 75.4 and 88.0%. In Expt. II the final fish weights were 750, 757 and 992g respectively; the related feed gain ratios were 1.68, 1.95 and 1.87 and the survival rates were 89, 91 and 95.2%. Dietary value of SDP at low water temperatures was also investigated (EXpt. III) by feeding 3 groups of 2-year old fish having average weights of 677, 750 and 1020g, for about six months from October to May. This experiment was the extension of Expt. I and the fish grew upto 1600, 1600 and 2000g respectively and the feed gain ratio ranged from 1.49 to 1.76.
These results demonstrate that the newly developed SDP is comparable or possibly superior in dietary value to raw fish and moist pellets which are commonly being used as feeds for yellowtail.

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The suitability of a combination of soybean meal (SBM), corn gluten meal (CGM), and meat meal (MM) as an alternative protein ingredient for fish meal in high energy dry pellet (DP) was examined for adult and juvenile red sea bream, Pagrus major. Fish weighing 565g and 35g on average were fed the experimental pellets containing combinations of SBM (20-30%), CGM (5-20%), and MM (3-6%) (replacing 42-62% of fish meal), for 85 and 56 days, respectively.
Adult fish fed all the combination diets showed the same growth rate and feed gain ratio as the control. In the case of juveniles, However, fish fed the diets containing CGM above 15% showed inferior performance and hemochemical characteristics.
These results demonstrated that a combination of SBM, CGM, and MM can succenfully replace 46-62% of fish meal in the DP for both adult and juvenile red sea bream though the CGM level should not be over 10% for juvenile fish.

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The Australian aquaculture industry in 1994/95 was worth about AU$ 419 million, and grows eleven main species. Significant research effort has been focused on the replacement of fish meal protein, for alternative proteins, more readily available within the country. Considerable research has been directed to techniques for the rearing of marine fish larvae and the adaptation of grow out technology to suit local conditions. Feed distribution technology is also an area receiving attention. The increasing cost of feed, the desire to improve husbandry techniques and a concern for the environment has prompted research into feed management and technology, particularly in the salmonid industry. Feed distribution technology using an underwater sensor with a ‘feedback’ algorithm was used to grow fish efficiently, displaying significant improvement over historical values. The relationship between fish behaviour/biology/feeding & activity rhythms is discussed in relation to the requirements for optimal growth and feed conversion of cultured fish. Three species were considered (S. salar, O. tshawytscha and L. calcarifer) and feeding patterns were demonstrated to relate to size, photoperiod, temperature and discussed in respect to fish hierarchies.

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In recent years large tracts of coastal lands are cleared by government bodies and private companies for shrimp and fish cultivation. These farms are usually located at banks of estuaries where the lands are low lying and subject to tidal influence. Intensive farming activities impose an heavy demand on water resources and the marine environment. The fragile aquatic ecosystems in these areas under pressure from both the aquaculture and urban activities. It is believed that with proper planning and farming methods the negative impact can be reduced cost-effectively for sustainable economic growth.

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