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Hatching rates and hatching times (50% hatch) of red sea bream, Pagrus major (Temminck & Schlegel), eggs in culture media that were prepared to dilute rotifer Brachionus plicatilis Muller extract at 4000-, 6000-. 8000- and 10 000-fold with artificial sea water (σ15, = 24.0) were investigated. Although differences in hatching rate between the culture media and control artificial sea water were negligible, hatching time was significantly shorter in media at 4000- and 6000-fold dilutions than in media at 8000- and 10 000-fold dilutions and in the control artificial sea water, when the eggs immediately post spawning were incubated. The hatching rates of eggs at three developmental stages, immediately post-spawning, gastrula stage and heart-beat initiation stage, incubated respectively in the medium at 6000-fold dilution and the control, did not differ either, yet the hatching times at each egg stage in the medium were significantly shorter than that in the control. These results suggest that hatching enzyme secretion from the hatching glands is promoted to perceive chemical stimuli in the water-soluble fraction of rotifer extract via the embryo's chemoreceptors, from the heart-beat initiation stage to immediately before hatching, thus shortening the hatching time.

A captive-raised Pacific bluefin tuna, Thunnus orientalis, 145.6 cm L T , 35.2 kg M, was found to be a hermaphrodite. This is the first record of hermaphroditism in this species.

Control and stressed groups of juvenile Japanese parrot fish Oplegnathus fasciatus were fed diets (moist pellet) supplemented with 0, 75, and 300mg of ascorbic acid (AsA) per 100g. Fish in the stressed group were intermittently exposed to decreasing water oxygen levels every 3 or 4 days for 16 weeks. In the fish given a diet containing no AsA supplement, AsA-deficiency symptoms were manifest-ed earlier, and to a greater extent, in the stressed fish than in the non-stressed ones. Similarly, the growth of stressed fish fed on a diet supplemented with 75mg AsA per 100g was inferior to the growth of the control group, and in the stressed fish there was a reduction in AsA levels in the plasma, kidneys, and gills. On the other hand, fish fed on a diet supplemented with 300mg of AsA per 100g were barely affected by the stressor. These results indicate that, in Japanese parrot fish under these experimental conditions, ex-posure to intermittent hypoxic stress not only induced AsA-deficiency disease early, but also in-creased the AsA requirement. It was also shown that high doses of AsA increased the ability of these fish to resist the stressor.

Summary The capability of planktonic yolk-sac larvae of red sea bream Pagrus major in detecting food was examined in the laboratory to ascertain basic knowledge on the early life history of this marine fish. After infrequent vertical burst swimming followed by slight rising or sinking, the larvae remained motionless within thin layers of concentrated food extract (rotifer, Brachionus plicatilis). At the moment of hatching, the larvae already have receptor cells with several cilia arranged radially in their open nostrils. Thus it is likely that by means of their vertical movement they are capable of sensing the thin food patch layer. We suggest that planktonic larvae of Pagrus major are capable of detecting and remaining within food patches even before the onset of feeding. The onset of food detection in the earlier stages may be, to some extent, the more efficient strategy for larval survival and growth because this ability could contribute to a reduction in energy consumption.

Feeding stimulants for the marbled rockfish Sebasticus marmoratus were identfied by the omission test uding the synthetic extract of krill Euphausia pacifica. The fish were fed on a purifiedcasein diet supplemented with constituents of the extract for 6 days. The feeding stimulant activity was evaluated by the daily feeding rate. The nucleotide fraction of the extract was the most effective, followed by the amino acid fraction which showed a littel activity. Inosine had the highest activity among all constituents of the extract. With increasing supplementary level to the diet, amino acids such as L-alanine, L-methionine, L-serine and L-proline and nucleotides such as adenosine-5'-diphosphate, adenosine-5'-monophosphate and inosine-5'-monophosphate became positive. When inosine together with, L-alanine, L-methionine, L-serine and L-proline was supplemented to the diet, its activity for the fish was remarkably improved, becoming to the synthetic extract.

Thyroid hormones (THs) are essential for the embryonic and post-embryonic development of fish. We studied the role of THs during the early, post-embryonic, development of Pacific bluefin tuna. Embryos were treated with L-thyroxine (T(4)) or the anti-thyroid drug methimazole (MMI), and reared in microtitre plates for 3 days. Immersion in MMI, but not T(4), led to retardation of retinal pigment epithelium (RPE) pigmentation 3 days post-hatching (dph). Concurrent immersion in T(4) and MMI had no effect of RPE pigmentation. We also measured the expression of TRalphaA, TRalphaB, and TRbeta mRNA using real-time RT-PCR. Treatment with MMI significantly reduced TRbeta mRNA expression. Taken together these results suggest that the development of RPE pigmentation is mediated by TH, most likely via TRbeta.

We studied the profiles of 3,5,3'-l-triiodothyronine (T3), thyroxine (T4), and thyroid hormone receptors (TRs) in Pacific bluefin tuna (Thunnus orientalis) during embryonic and post-embryonic development. Both T3 and T4 were detected in embryos just before hatching, and it was found that the levels of both were increased in postflexion fish. The thyroid follicles were increased in both size and number in postflexion fish compared with preflexion fish. A TRbeta cDNA clone was generated by RACE. Two TRalpha cDNA clones were also partially identified and analyzed by real-time RT-PCR in this study. The TR mRNA levels in embryos were determined, and these were found to be lower than those in preflexion fish. Therefore, we considered that thyroid hormones function during early post-embryonic development as well as during embryonic development. Moreover, there was a peak in the TR mRNA level during postflexion stages, as seen during metamorphosis in Japanese flounder and Japanese conger eel. It is possible that thyroid hormones control the early development of scombrid fish through TRs, as they do for Pluronectiformes and Anguilliformes.

A cDNA encoding transthyretin was cloned from the Pacific bluefin tuna (Thunnus orientalis). This cDNA contains a complete open reading frame encoding 151 amino acid residues. The deduced amino acid sequence is 81% and 55% identical to the gilthead seabream and common carp forms, respectively, and 33-39% to mammalian, reptilian, and amphibian forms. A 1.0-kb transcript was found in the the liver and ovary; the liver is the main source of this protein. Analysis of triiodo-L-thyronine (T(3)) and L-thyroxine (T(4)) binding demonstrated that both T(3) and T(4) bind to bluefin transthyretin. The binding activity of T(3) for bluefin transthyretin is higher than that of T(4). These results indicate that bluefin transthyretin acts as a transporter of thyroid hormones (THs) in the plasma, and plays an important role in the function of THs in target cells.

Summary Human melanocytes respond to UV irradiation by increasing the synthesis of melanin. While much is now understood of the pathways governing this process and the nature of the melanin synthesized, little is known of melanins produced by lower vertebrates and their capacity to respond to UV. Here we report that a fish, red seabream, can undergo ‘suntanning’. Histological, colorimetric and chemical assays were performed for suntanned red seabream fish bred in net cages to analyse the melanins and compared with shaded or wild red seabream fish. For color evaluation, the L* values of suntanned fish were dramatically lower than those in the other two groups. Pyrrole-2,3,5-tricarboxylic acid (PTCA), an indicator of eumelanin, was detected in suntanned fish at five times higher levels than in shaded or wild fish while 4-amino-3-hydroxyphenylalanine (4-AHP), a marker for pheomelanin, could not be detected in any of the samples. Histological analysis showed that melanocytes in the suntanned skin enlarged and increased in number to form a monolayer at the surface of the skin. Analysis of L* values and PTCA levels showed quite a high correlation coefficient (r ¼ )0.843). When comparing shaded and wild red seabream fish, the scores were closer but some significant differences were still found in some body areas. These results indicate that eumelanin accumulates in suntanned fish during the increase in skin color, which is induced by sunlight, presumably by ultraviolet radiation.

A croaker (Nibea mitsukurii) has a high incidence of the skin melanoma, chromatophoroma, in a Pacific coastal area in Japan. A sea catfish (Plotosus anguillaris) bearing skin melanosis is also found in the same area. For elucidation of a correlation between these pigment cell neoplasms of the skin and environmental contaminants, an epidemiological survey was conducted to determine the distribution and prevalence of tumor-bearing fish. Based upon observations of a high prevalence of skin neoplasms near the discharge point for kraft pulp mills, experiments were conducted to determine the neoplastic induction efficiency of the effluent on the croaker and sea catfish species. Isolation and identification of mutagens in effluent extracts were carried out using the Ames test, followed by mass spectral analysis of mutagenic fractions. The effluent induced a chromatophoroma on one croaker of the 100 tested, and it induced pigment cell hyperplasia on 70 to 100% of the sea catfish. These skin neoplasms were grossly similar to those observed in the field. Five chloroacetones were identified from the Ames-positive fractions of the effluent, and tetrachlorocyclopentene-1,3-dione and two α-dicarbonyl compounds were also detected as mutagens. The above experiments indicate that the mutagenic contaminants found in kraft mill effluent may play an important role in the induction of skin neoplastic disease in fish.

The digestive system in the ocellate puffer was histologically and biochemically examined. Also, the effect of scallop extract as a flavor in a diet on performance of the puffer was investigated.The ocellate puffer lacks a stomach, resulting that its expansion sea observed only esophageal epithelium and expansion sac-epithelium and that pepsin-like activity in the digestive tract from the esophagus to the opening portion of bile duct, excluding the expansion sac, maintained an extremely low level.Performance of the puffer fed the flavored diet for 20 days was much better than that fed the unflavored diet. Better protein digestibility was also recognized in the puffer fed the flavored diets. These findings suggest that favorite chemical stimuli caused by the dietary supplementation of the flavor promot digestive and absorptive functions even in the ocellate puffer having no stomach.

The effect of algae as feed supplementary was determined on yellow tail Seriola quinqueradiata in terms of serological parameters and proximate composition of the dorsal muscle. Fish of 144g in body weight were reared for 60 days in floating nets. Control group was fed on sand lance Ammodytes personatus.One percent of hot water-extract from Chlorella vulgaris (Chlorella-extract group) or 0.5% of kelp Laminaria digitata (kelp meal group) was supplemented to the above basal diet (sand lance). The supplementaries had no effect on body weight gain or feed conversion efficiency. The kelp meal depressed the lipid, non-protein nitrogen, and amino nitrogen levels in the serum, and elevated the muscle lipid level. Chlorella-extract, however, did not cause significant alteration in serum constituents and proximate composition of the muscle.After 60 days of feeding, the fish were kept in indoor tanks without feeding for 23 days. Body weight loss was not significantly distinct among the 3 groups. Nevertheless, the serum lipid and nonesterified fatty acid levels were characteristically changed under the starvation period in response to the dietary regimen. The muscle lipid loss was higher in the kelp meal group than the control group. Furthermore, the suppression of breakdown of muscle protein was found in the Chlorella-extract group and the kelp meal group.These results showed that the kelp meal contributed to accelerate the lipid deposition to the muscle and to mobilize the lipid to energy. The importance of algae supplement in yellow tail, was discussed in relation to improvement of lipid metabolism which had a close connection with the health condition of the fish.

Chromatophoroma in the croaker (Nibea mitsukurii) showed a unique geographic distribution. The contribution of environmental chemicals to the cause of chromatophoroma in the feral croaker is considered likely on the basis of the following results in our studies. 1) Chromatophoroma was induced in tank-reared N. mitsukurii by administration of certain kinds of known carcinogens such as 7,12-dimethyl-benz(a)anthra-cene, N-methyl-N'-nitro-N-nitrosoguanidine, and nifurpirinol. 2) Local accumulation of pigment-cell hyperplasia in the catfish (Protosus anguillaris) showed similar tendencies to those of chromatophoroma in N. mitsukurii. 3) Removal of contaminated sediment from the harbor and the river appeared to reduce the incidence from 47% in 1973–1983 to about 20% in 1985–1987. 4) Waste water from a factory located at the station where the incidence of the neoplasm was the highest contained mutagenic substances such as chloroacetones and glyoxals [5]. Exposure of catfish to the waste water induced pigment-cell hyperplasia on the skin. J Invest Dermatol 92:248S–254S, 1989

The nutritional disease of yellowtail Seriola quinqueradiata caused by feeding on raw sardine Sardinops melanosticta was diagnstically investigated by comparison with fish fed on sand lance Ammodytes personatus as a control. Fish fed on sardine showed retardation of growth, high mortality, and low feed conversion effciency. In the diseased fish, hematocrit value, serum albumin level, and serum lactate level were significantly lowered. The serum contained extremely large amounts of lipoperoxide, which specifically conjugated with lipoprotein of globulin fraction. The electrophoretic belavior of serum protein and liporprotein were considerably changed. Obvious pathological symptoms appeared in the kidney; necrosis of the tubular epithelia and numerical atrophy of the hematopoietic tissue, which would correlate to high ammonium-nitrogen and low urea-nitrogen levels in the serum. Nothing peculiar was seen in the spleen, gills, and digestive ducts. These results of the diagnostic investigation revealed that the disease caused by sardine feeding was appreciably different from a nutritional one caused by anchovy feeding.

The visual cell morphology in 2-90mm long larvae and juveniles, and adult of the red sea bream Pagrus major was examined histologically. The visual system of the larvae is poorly developed at hatching, but becomes functional in 36 hours. At this time, the eyes are well pigmented, cones are formed, and optic nerves connect with the optic tectum. The visual cells of larvae smaller than 10.6mm are all single cones. At 11mm TL, the single cones fuse to form twin cones, and rods appear at the same time. Red sea bream shifts from a pelagic to a benthic habitat when about 12-15mm long. The observed increase in visual sensitivity at 11mm appears to be a preadaptation to life at greater depths. Likewise, the specialized retinal region for acute vision shifts from temporal to dorso-temporal at a length of 30mm, implying a change in visual axis from fore to lower-fore direction, and an adaptation to the change in diet from planktonic to benthic animals.