Hybridization success of three common European cyprinid species, <Emphasis Type="Italic">Rutilus rutilus,Blicca bjoerkna</Emphasis> and <Emphasis Type="Italic">Abramis brama</Emphasis> and larval resistance to stress tests

ABSTRACT:   Hybridization success at early developmental stages and larval resistance to osmotic, thermal and fasting tests in roach Rutilus rutilus , silver bream Blicca bjoerkna , common bream Abramis brama and their F1 hybrids were investigated. Results revealed that hybrid survival rates were similar to parents. At the eyed embryo stage, however, a maternal effect was observed as a general trend during hatchling and larval stages. After these stages, hybrids displayed a higher survival rate than their parents. Under stress tests, no survival was observed after 40 min for osmotic and thermal shocks and after 24 days for the prolonged fasting test in these species and their F1 hybrids. The median survivals of hybrids were intermediate between the two parents. For total mortality, hybrids were also affected by a maternal effect but to the advantage of the hybrids.     

Association between bacterial community structures and mortality of fish larvae in intensive rearing systems

Bacterial community structures were analyzed in water used for rearing fish larvae by fluorescence in situ hybridization. In Experiment 1, red sea bream Pagrus major larvae were reared in two commercial seed production tanks. The survival rate in Tank 1 was higher than in Tank 2, even though phytoplankton, Nannochloropsis sp., was added to both tanks. In Tank 2, γ-proteobacteria became dominant (∼70% of total bacteria) on day 13, there after heavy larval mortalities occurred. In Tank 1, however, α-proteobacteria and the Cytophaga-Flavobacterium cluster were predominant from day − 1 until day 13; no significant mortality was recorded. In Experiment 2, marble goby Oxyeleotris marmoratus larvae were cultured with or without Nannochloropsis sp. At the end of the experiment, larval survival rates in aquaria with Nannochloropsis sp. were significantly (P <0.05) higher than those without. In rearing water without Nannochloropsis sp., γ-proteobacteria increased during rearing. In rearing water with Nannochloropsis sp., α-prote obacteria and the Cytophaga-Flavobacterium cluster were predominant at the beginning of the experiments and the relative abundance of γ-proteobacteria was maintained at a lower level throughout the experiments. The predominance of α-proteobacteria and the Cytophaga-Flavobacterium cluster appears to be a good indicator of successful larval production.     

Induction of (<Emphasis Type="Italic">Z</Emphasis>)-8-heptadecene in marine green alga <Emphasis Type="Italic">Bryopsis maxima</Emphasis> by mechanical wounding

ABSTRACT:   After mechanical wounding of the marine green alga Bryopsis maxima in a phosphate buffer, one main organic component was released to the solution. The organic compound was characterized by a molecular ion at 238  m/z by gas chromatography–mass spectrometry (GC-MS) and was deduced as 8-heptadecene by the fragment pattern. To identify the stereochemistry of 8-heptadecene, synthetic ( Z / E )-8-heptadecene was coinjected to the solution of wounded B. maxima . Comparing retention times and mass spectra with the synthetic sample, the target hydrocarbon obtained from wounded B. maxima was coincident with ( Z )-8-heptadecene.     

Tench (<Emphasis Type="Italic">Tinca tinca</Emphasis> L.) larvae rearing under controlled conditions: density and basic supply of <Emphasis Type="Italic">Artemia</Emphasis> nauplii as the sole food

After artificial reproduction of tench, larvae must be maintained indoors, and studies on rearing conditions are needed, focussing on the reduction of labour and costs. Three experiments on larvae (5th day post-hatch) were conducted for 25 days using Artemia nauplii as the sole food in order to determine basic feeding and density conditions during the first rearing period. Tench were maintained in 25 l fibreglass tanks, supplied with an artesian water flow throughout of 0.2 l min⁻¹. Water temperature was 22.5 ± 1°C, and the photoperiod was natural. Larvae fed on a restricted amount of nauplii reached high survival rates, even with the minimum of 50 nauplii larva⁻¹ day⁻¹. This amount of food may be sufficient at least for the first 25 days of exogenous feeding if fast growth is not the priority, and high densities can be maintained with good survival rates (over 90% up to 160 larvae l⁻¹ and 77% with 320 larvae l⁻¹). When food was supplied in excess once a day, high survival rates were achieved (91–97%), without differences among the densities tested. Animals at a density of 100 l⁻¹ reached the highest length (15.57 mm) and individual weight (46.8 mg). This growth is greater than those reported in studies feeding several times a day. It could be deduced that, while live food remains available for tench, it is not necessary to feed so frequently. Considering the relationship among the initial number of animals, final survival and growth and ration supplied, the new data reported here are useful to establish suitable stocking densities under both culture and experimental conditions.     

Masculinization of Convict Cichlid (<Emphasis Type="Italic">Cichlasoma nigrofasciatum</Emphasis>) by immersion in <Emphasis Type="Italic">Tribulus terrestris</Emphasis> extract

We have examined the effects of Tribulus terrestris (TT), a non-toxic herb, on sex reversal in the Convict Cichlid Cichlasoma nigrofasciatum with the aim of introducing a new environmentally friendly method for masculinization in C. nigrofasciatum. TT is a natural plant product that elevates the testosterone levels in humans and animals. Different concentrations (0.0, 0.10, 0.20 and 0.30 g/l) of TT extract were tested for their effect on sex reversal in C. nigrofasciatum by immersing newly hatched offspring once weekly for 2 months in TT extract. Of the dosages used in the present study, 0.30 g/l TT was the most effective in terms of masculinization, resulting in a maximum male ratio of 87.23% (P < 0.001). Sex ratios of 79 and 85% at 0.10 and 0.20 g/l TT, respectively, were also significantly different from the expected 1:1 ratio (P < 0.001). Histological examinations revealed that the testes of fish treated with TT extract contained all stages of spermatogenesis, clearly demonstrating that the administration of TT extract to C. nigrofasciatum stimulated spermatogenesis. Total survival rates in all treatments and the control were uniformly high, ranging from 88.57 to 90% (P > 0.05). We concluded that TT had no negative effect on the survival rate of C. nigrofasciatum. In addition, all groups of TT-treated fish exhibited successful growth acceleration compared to the control group, but only the 0.30 g/l TT treatment significantly improved the growth rate of C. nigrofasciatum. (P < 0.01). Sex reversal in C. nigrofasciatum demonstrated that TT-treated 0-day-old larvae showed successful sex reversal, spermatogenesis and a better growth rate than untreated progenies.     

Effects of fish size and water temperature on the acute toxicity of boron to Japanese flounder <Emphasis Type="Italic">Paralichthys olivaceus</Emphasis> and red sea bream <Emphasis Type="Italic">Pagrus major</Emphasis>

ABSTRACT:     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.     

Optimum temperature and salinity conditions for growth of green algae <Emphasis Type="Italic">Chlorella ellipsoidea</Emphasis> and <Emphasis Type="Italic">Nannochloris oculata</Emphasis>

ABSTRACT:   The effects of temperature and salinity on growth of green algae Chlorella ellipsoidea and Nannochloris oculata were determined to compare the optimum culture conditions. A four-temperature (15, 20, 25, and 30°C) × three-salinity (10, 20, and 30) factorial design with triplicates was applied. Specific growth rate (SGR), maximum density, and duration to reach maximum density of C. ellipsoidea were significantly affected by both temperature and salinity. The highest SGR was observed in C. ellipsoidea at 25°C and salinity 10, but the maximum density was very low. The highest maximum density was achieved in C. ellipsoidea at 15°C and 10. The slope constant of the linear relationship between semilogarithmic growth of C. ellipsoidea and day of culture was highest at 15°C and 10. The SGR and duration to reach maximum density of N. oculata were significantly affected by both temperature and salinity. However, maximum density of N. oculata was significantly affected by temperature, but not salinity. The highest maximum density was achieved in N. oculata at 25°C and 30, but SGR was significantly lower than that of N. oculata at 25°C and 10. The slope constant of the linear relationship between semilogarithmic growth of N. oculata and day of culture was highest at 25°C and 30. Based on these results, the condition of 15°C and salinity 10 seemed to be optimal for maximum density of C. ellipsoidea , and the condition of 25°C and 10 and 30 for SGR and maximum density for N. oculata , respectively.     

Improvement of larval rearing technique for mass seed production of snow crab <Emphasis Type="Italic">Chionoecetes opilio</Emphasis>

Larval rearing experiments were conducted to examine the potential for mass seed production of the snow crab Chionoecetes opilio using a total of eight 20-kL tanks. Tanks were equipped with agitators, which move the water using a rectangular blade to prevent the zoeas sinking to the bottom of the tank. Larval rearing water was treated with sodium nifurstyrenate once a week to reduce the chance of larval infection by pathogenic bacteria. Zo eas were fed with rotifers and Artemia nauplii. A total of 122 830 megalops and 16 660 first-stage crabs were produced. Thus, the potential for mass seed production of snow crab was determined. Survival rates up to the megalopal stage were high in tanks with a feeding regime that fed rotifers to larvae through an entire zoeal stage. This study also describes the fatty acid composition of snow crab larvae. It revealed that the first zoeas had a high DHA content and DHA/EPA ratio, but these values significantly decreased in the second stage zoeas and megalops. Improving the DHA content and/or DHA/EPA ratio of larvae should be important in studies on mass seed production technology of the snow crab.     

<Emphasis Type="Italic">Myxobolus nagaraensis</Emphasis> n. sp. (Myxozoa: Myxosporea) causes abdominal distension of freshwater goby <Emphasis Type="Italic">Rhinogobius</Emphasis> sp. OR type from the Nagara River

ABSTRACT:   A new myxosporean parasite was found in the body cavity and caudal peduncle of the freshwater goby Rhinogobius sp. Orange type (OR) collected from the Nagara River, Gifu Prefecture, Japan. Infected fish exhibited substantial swelling of the abdomen caused by large parasitic cysts approximately 10 mm in size, formed in the visceral cavity. The cyst was a compacted aggregate of several smaller cysts, similar to a bunch of grapes in appearance. Histological examination showed that plasmodia developed within the renal capsule, and finally occupied the visceral cavity. Spores were ovoid with an attenuated anterior end. Sutural ridges were conspicuous with several folds on the edge. Average spore size was 11.9 (10.5–13.5) μm long, 9.0 (8.0–10.0) μm wide, and 6.5 (6.0–7.0) μm thick. Two equal polar capsules were 5.5 (4.5–6 0) μm long and 3.0 (2.5–4.0) μm wide. Partial small subunit ribosomal DNA sequences of the myxosporean were distinct from those of other myxozoan species in GENBANK. A new species name, Myxobolus nagaraensis , is proposed for this parasite.     

Identification of a telomere sequence type in three sponge species (Porifera) by fluorescence <Emphasis Type="Italic">in situ</Emphasis> hybridization analysis

The telomere sequence type (TTAGGG)_n is known to be distributed in various phyla in the Animalia and in Mastigophora (Protista). However, the telomere type of Porifera (sponges), a phylum comprising the lowest multicellular animals, has not been reported. In this study, we examined the three sponge species Leucetta chagosensis, Halichondria japonica, and Halichondria panicea for the presence of the telomere type (TTAGGG)_n by fluorescence in situ hybridization (FISH). The oligonucleotide probe (TTAGGG)₇ clearly displayed signals on the interphase nuclei of all three sponges. In contrast, the (TTAGG)₇ probe, which has one base fewer than (TTAGGG)₇, did not display the signals. These results suggest that the telomeres of the three sponges consist of (TTAGGG)_n, which is identical to the sequence type found in many higher multicellular animals and in Mastigophora. Additionally, this is the first study to reveal a telomere sequence type for Porifera. Moreover, these results suggest that Porifera are phylogenetically related to Mastigophora, and supports the general theory that Porifera evolved from Mastigophora. Further, this study strongly suggests that the origin of the (TTAGGG)_n telomere sequence is to be found in a common ancestor of either the Bilateria and Porifera, or the Protista.     

Characteristics of burnt meat in cultured yellowtail <Emphasis Type="Italic">Seriola quinqueradiata</Emphasis>

ABSTRACT:   In order to understand the characteristics of burnt meat in cultured yellowtail Seriola quinqueradiata , fish were kept at two different temperatures (13 and 30°C) and slaughtered by either spinal cord destruction (SCD) or suffocation in air (SA). Early postmortem changes during storage at 32°C were analyzed by rheological, biochemical, and histological methods. The burnt meat (with lightness parameter, L* ≥ 55) was observed at 1-h storage in the SA 30°C group, at 2 h in SCD 30°C, and at 4 h in SA 13°C; meat was normal for the SCD 13°C group until 6 h of storage. Breaking strength scores were higher for the normal meat (200 g/cm²) than burnt meat (70 g/cm²) at 4 h of storage. Expressible water content was higher for the burnt meat than for the normal meat. Adenosine triphosphate concentrations for the SCD groups were higher than for the SA counterparts. Moreover, pH decrease was much faster in the 30°C groups, showing pH 5.6 at 2 h of storage. A negative correlation between the pH and lactic acid contents in muscle ( P  < 0.001) was found. Histological analysis evidenced a larger pericellular area (40%) in the burnt samples than in the normal samples (16%). It was confirmed that a higher fish-keeping water temperature and a stressful slaughter method (faster glycolytic process) were determinative factors that influence the occurrence of burnt muscle in yellowtail, and that the effect of the former is larger than the latter.     

Improving growth in juvenile turbot (<Emphasis Type="Italic">Scophthalmus maximus</Emphasis> Rafinesque) by rearing fish in switched temperature regimes

The effect of thermal history (16 and 20°C) on growth of juvenile turbot, Scophthalmus maximus (initial mean weight 72.6 g, n = 157) was studied. Fish were divided into four groups, two groups remaining at constant temperature (C16, C20), while fish in the other groups were transferred from either 16 to 20°C (F16-20) or from 20 to 16°C (F20-16). Between 35 and 42 fish in each tank were individually tagged at the start of the experiment. The final mean weights were significantly higher in the F20-16 group (230 g) than in the C20 (213 g), F16-20 (211 g) and C16 (205 g) groups. The overall growth rate was highest in the F20-16 group (1.17% day⁻¹) but comparable in the three other groups (1.00–1.04% day⁻¹). Our findings indicate that, even at near-optimal temperature for a given size, the temperature history of the fish may influence future growth. Based on these indications, we conclude that as turbot grow larger, the temperature should be reduced to take advantage of the change in optimal temperature for growth with increasing fish size rather than rearing at constant temperatures.     

Settlement of larval top shell <Emphasis Type="Italic">Turbo (Batillus) cornutus</Emphasis> in response to several marine algae

ABSTRACT:     The settlement of larval top shell Turbo  ( Batillus )  cornutus in response to seven macroalgal and three benthic diatom species was examined in the laboratory. The percentages of larval settlement differed significantly among algal species, and were significantly higher on two red algal species ( Marginisporum crassissima , an articulated coralline alga, and Gelidium elegans , an agarophyte) than on the green algae, brown algae and benthic diatoms tested. Marginisporum crassissima induced larval settlement most strongly throughout the experiments. The percentage of larval settlement on a crustose coralline alga (unidentified species), which is known as a suitable substratum for abalone larvae, was much lower than on M. crassissima and G. elegans , which have morphologically complex growth forms . The percentage of settled individuals on ethanol-killed M. crassissima was much lower than on intact M. crassissima . The results indicate that physical structure is unlikely to be the main inducer of settlement; therefore, settlement of top shell larvae seems to be strongly induced by chemicals from the two red algal species. The specific distribution of juvenile top shell in the field may be at least partly determined by the strong induction of larval settlement by articulated coralline and gelidiacean algae.     

Effects of stocking density on survival and growth of juvenile tench (<Emphasis Type="Italic">Tinca tinca</Emphasis> L.)

In two 120-day experiments, performed in the laboratory at 22°C, the effects of stocking density on the survival and growth of juvenile tench (Tinca tinca L.) were evaluated. Fish were kept in fibreglass tanks, supplied throughout with flow of artesian water, and fed a dry diet for salmonids, in excess, supplemented with restricted amounts of Artemia nauplii. In the first experiment four-month-old juveniles (0.31 ± 0.04 g and 32.00 ± 1.17 mm TL) were stocked at four densities—0.18, 0.88, 1.05, and 2.10 g l⁻¹. Survival was high (>89%) for all treatments. Final densities ranged between 1.10 g l⁻¹ (significantly lowest) and 10.46 g l⁻¹ (significantly highest). The density increase was significantly higher (611%) for fish stocked at the lowest initial density (0.18 g l⁻¹) than for fish stocked at 0.88, 1.05, and 2.10 g l⁻¹, for which the density increase averaged 457%. In the second experiment, 4.5-month-old juveniles (0.58 ± 0.17 g and 39.54 ± 0.83 mm TL) were stocked at three densities—1.05, 3.00, and 4.00 g l⁻¹. Survival was high (>96%) for all treatments. Final densities ranged between 4.08 and 16.53 g l⁻¹ and were significantly higher for greater initial densities. The density increase was greatest (413%) for fish stocked at the highest density (4 g l⁻¹) and was not significantly different for fish stocked at 1.05 and 3 g l⁻¹. Considering all the densities in the two experiments, for stocking at 4 g l⁻¹ the final density was 15 times higher than that reached after stocking at 0.18 g l⁻¹, without harmful effects on survival and growth. This final density (equivalent to 16.53 kg m⁻³) is in the range recommended for other fish species in this period under intensive conditions.     

Annual variation of potential predation impacts on larval and juvenile marbled sole <Emphasis Type="Italic">Pseudopleuronectes yokohamae</Emphasis> by sand shrimp <Emphasis Type="Italic">Crangon uritai</Emphasis> in Hakodate Bay,Hokkaido

An investigation was conducted to evaluate the annual variation in potential predation impact (PPI) on larval and juvenile Pseudopleuronectes yokohamae by Crangon uritai in Hakodate Bay using predator-prey size relationships. Laboratory experiments were designed to estimate the favorable prey size of C. uritai through back-calculation of body length (BL) of P. yokohamae from sagittal otolith diameter observed in the stomachs of C. uritai. The most favorable prey-predator size ratio (BL of P. yokohamae-total length (TL) of C. uritai) class was 0.15–0.19, and ranged from 0.12–0.31. There was a significant positive correlation between the BL increase of P. yokohamae and the bottom water temperature in the field, such that BLs stagnated during the cold year of 1999 from April to June, and increased during the warm year of 2002. In contrast, no significant correlation was found between the TL increase of C. uritai and the bottom water temperature. Moreover, there were no significant differences in the mean TL of C. uritai between months (April–June) or years (1998–2002). Variation of PPI depended on the relationships between the growth rates of P. yokohamae and bottom water temperature. Therefore, the warm year of 2002 resulted in higher potential predation impact (PPI≥20), and it was at least 20 days shorter than that of the cold year of 1999. These results suggest that increased bottom water temperature in the nursery area was one of the most important factors for cumulative predation loss.     

Effects of heavy metals in river waters in Japan on immobility and mortality of <Emphasis Type="Italic">Daphnia magna</Emphasis> and <Emphasis Type="Italic">Oryzias latipes</Emphasis> larvae

ABSTRACT:   Samples of river waters containing high concentrations of zinc and other heavy metals but low concentrations of other anthropogenic contaminants were collected to investigate the relationship between toxicity of heavy metals and naturally present organic matters or hardness, as well as the effects of heavy metals on aquatic organisms. Acute toxicity tests were conducted for the water samples using Daphnia magna and medaka Oryzias latipes . Almost all the D. magna died in river waters containing high concentrations of zinc, but O. latipes in the same waters were hardly affected. Since the test organisms were not only exposed to zinc but also other heavy metals in the river waters, we examined the toxicity using toxic units composed of zinc, copper, lead, and cadmium. The results of a bioassay with the river waters showed that the mortality of D. magna did not depend solely on the total number of toxic units of heavy metals. The organic matters and the hardness of the river waters could decrease the acute toxicity of zinc and other heavy metals to D. magna .     

Effects of capture,loading density and transport stress on the mortality,physiological responses,bacterial density and growth of rohu <Emphasis Type="Italic">Labeo</Emphasis><Emphasis Type="Italic"> rohita</Emphasis> fingerlings

This study evaluated the effects of three levels of loading density (200, 300 and 400 g L⁻¹) and four levels of duration (1, 3, 6 and 9 h) on the mortality, plasma cortisol and chloride levels and growth of rohu Labeo rohita fingerlings in a transport simulation. While total immediate mortality was low (4–12%), delayed mortality was high (27–49%). Initial capture and handling were found to constitute the most stressful phase as indicated by elevated plasma cortisol. The levels of cortisol continued to rise at 6 and 9 h after transport, with the highest level observed at 9 h after transport. The level of plasma chloride fell after transport across all density levels and treatment durations. Specific growth rate (SGR, %/day) and total bacterial density (cfu/g) were not different between and within treatments, and between treatments and the controls. This study demonstrates that transport has a profound effect on the stress responses of rohu fingerlings. Although the level of immediate mortality was low, the higher level of delayed mortality has serious implications in terms of production inefficiency for grow-out farmers.     

Size selectivity of escape holes in conger tube traps for inshore hagfish <Emphasis Type="Italic">Eptatretus burgeri</Emphasis> and white-spotted conger <Emphasis Type="Italic">Conger myriaster</Emphasis> in Tokyo Bay

ABSTRACT:   In Tokyo Bay, conger tube-trap fishers voluntarily deployed escape holes of at least 13 mm diameter to reduce the by-catch of young conger smaller than the marketable size of 35 cm total length. Comparative fishing experiments in Tokyo Bay were carried out using tube traps with seven hole diameters (3, 9, 13.5, 14, 15, 17, and 19 mm), to obtain the size-selectivity of the escape-hole size for inshore hagfish Eptatretus burgeri and white-spotted conger Conger myriaster . On the assumption of the geometrical similarity in the combination of body g and hole perimeter m at a given retention probability, a single master curve s ( R ) = exp(−13.52 + 11.31 R )/(1 + exp [−13.52 + 11.31 R ]) was estimated for the two species in terms of relative R  =  g / m using the Share Each LEngth's Catch Total (SELECT) process based on a multinomial distribution. Almost all conger and hagfish with a girth equivalent to the hole perimeter were able to pass through the hole. Thus, the two species have a high ability to escape through a narrow space by squeezing the body through the hole in the rigid PVC tube. Optimum escape-hole size is discussed from several objectives for conger tube-trap fishery management, e.g. reduction of hagfish by-catch. This study also specifies the conditions for pooling data when fishing experiments using more than two fishing gears are replicated.