Growing depth limit of <Emphasis Type="Italic">Zostera caulescens</Emphasis> in coastal waters along the Japan Sea coast of Honshu,Japan

There is a possibility that deep coastal marine macrophytes will be less critically affected by thermal stress associated with climate change and remain as refugia. Thus, information on them is expected to contribute to conservation of biodiversity in coastal areas affected by climate change. To document the deep-growing Zostera caulescens in relation to the light environment, field surveys were conducted in coastal waters of the central area along the Japan Sea coast of Honshu, Japan, and then the relationship between the light environment and seagrass depth limit was examined. In the coastal waters of Sado Island and Noto Peninsula, the presence of deep coastal communities of Z. caulescens was confirmed in the depth range of 20–25 m. Biomass and shoot density for Z. caulescens, ranging 34.1–51.3 g DW m^?2 and 83–112 shoots m^?2, were recorded at a depth of 20 m in Ryotsu Bay, Sado Island. For the genus Zostera including the deep-growing Z. caulescens, the relation between the extinction coefficient and seagrass depth limit was described by the fitted regression equation. The minimum light requirement of the deep-growing Z. caulescens was markedly lower than that of the shallow-growing Zostera marina.     

<Emphasis Type="Italic">Neoheterobothrium hirame</Emphasis> (Monogenea) alters the feeding behavior of juvenile olive flounder <Emphasis Type="Italic">Paralichthys olivaceus</Emphasis>

We monitored feeding behavior and survival of starved juvenile olive flounder experimentally infected with the gill monogenean Neoheterobothrium hirame. Infected flounder increased amount of the time spent in the water column by 117% when trying to capture live mysids, Neomysis sp. They also showed different feeding patterns from those of uninfected fish and made fewer attacks towards prey during one feeding attempt. Although the average numbers of mysids captured by individuals were similar between infected and uninfected fish, heavily infected fish tended to catch less prey. These results indicate that N. hirame reduces the feeding efficiency of the host for capturing live prey and possibly makes them more vulnerable to predation during feeding. We could not detect any obvious difference in survival rates between uninfected, lightly and heavily infected fish during 3 months of starvation. There was no evidence that starvation makes fish more susceptible to N. hirame. The present study provides first experimental evidence that N. hirame affects feeding behavior of juvenile olive flounder and supports the idea that this parasite indirectly reducing the host’s survival and may be responsible for the recent reduction of the flounder population in Japan.     

Relationship between light and diel vertical migration of <Emphasis Type="Italic">Diaphus theta</Emphasis> and <Emphasis Type="Italic">Euphausia pacifica</Emphasis> off eastern Hokkaido

Underwater irradiance in sound-scattering layers (SSLs) during diel vertical migration (DVM) of marine organisms was investigated by a drifting vessel at locations in the western North Pacific during the period August 24–27, 2008. The inhabitants of the layers were identified via sampling as Diaphus theta, a type of myctophid fish, and Euphausia pacifica, a species of zooplankton. Underwater irradiance was estimated by the Beer–Lambert law using irradiance measurements on the deck and the diffuse attenuation coefficients obtained in the water. During DVM, the mean irradiances at 490 nm at the lower and upper boundaries of the SSL composed of E. pacifica were ?54.0 and ?45.3 dB, respectively. In contrast, the values for the boundaries of the D. theta SSL were ?82.5 and ?59.3 dB, respectively. It was possible to distinguish between D. theta and E. pacifica based on these ranges and the differences between the mean volume-backscattering strength (ΔMVBS) at 120 and 38 kHz. It was also possible to distinguish between D. theta/E. pacifica and other causes of scattering more clearly using these two parameters together than when using the ΔMVBS parameters separately. Our results suggest that underwater irradiance is an important parameter for discriminating among organisms in DVM.     

Pathological characteristics of olive flounder <Emphasis Type="Italic">Paralichthys olivaceus</Emphasis> experimentally infected with <Emphasis Type="Italic">Streptococcus parauberis</Emphasis>

Pathological characteristics of olive flounder Paralichthys olivaceus experimentally infected with Streptococcus parauberis were studied. Various stressful conditions, aeration and netting stress in particular, led to induced mortality by S. parauberis. Netting stress-induced mortality was positively correlated to bacterial dose and stressful conditions. Inflammation of the heart and pericarditis was the major pathological change observed in olive flounder experimentally infected with S. parauberis. During the infected period, the number of bacteria in the infected olive flounder was recorded over time. S. parauberis remained in all fish organs tested, especially in the heart and brain.     

Homogeneity of <Emphasis Type="Italic">Streptococcus dysgalactiae</Emphasis> from farmed amberjack <Emphasis Type="Italic">Seriola dumerili</Emphasis> in Japan

Streptococcus dysgalactiae strains have been isolated from cultured amberjack Seriola dumerili and yellowtail Seriola quinqueradiata in Japan. To characterize the fish isolates, we performed genetic analysis and compared the biochemical properties of these isolates with those of the S. dysgalactiae subsp. dysgalactiae and S. dysgalactiae subsp. equisimilis strains isolated from mammals. The genetic analysis revealed that the fish isolates were genetically very similar to each other with high DNA–DNA relatedness (>95.4%) and sequence homology. Meanwhile, the DNA relatedness between mammalian isolates and the fish isolates was 73.4–82.6%. In biased sinusoidal gel electrophoresis (BSFGE) analysis, the restriction patterns of mammalian isolates were different from those of fish isolates. The fish isolates did not show streptokinase activity in plasminogen obtained from mammals. These characteristics enabled us to distinguish between the fish isolates and the Sdd and Sde strains isolated from mammals. In order to obtain epidemiological information on the fish isolates, BSFGE patterns from 284 S. dysgalactiae strains from fish in Japan were examined. Based on the results of BSFGE analysis, the fish isolates were classified into 16 groups (AP1–AP16) with restriction enzyme ApaI. The dendrogram based on BSFGE analysis indicated that all fish isolates using in this study were closely related.     

Induction of diploid gynogenesis in turbot <Emphasis Type="Italic">Scophthalmus maximus</Emphasis> with left-eyed flounder <Emphasis Type="Italic">Paralichthys olivaceus</Emphasis> sperm

Turbot Scophthalmus maximus exhibits sexually dimorphic growth, with females growing faster and reaching larger adult sizes than males. Thus, development of techniques for preferentially producing females is necessary to optimize production of these species. In this paper, gynogenetic diploids of turbot were induced by activating egg development with ultraviolet (UV)-irradiated left-eyed flounder Paralichthys olivaceus sperm combined with cold shock to prevent extrusion of the second polar body. The results of UV irradiation experiments showed that survival, motility, and duration of activity of P. olivaceus sperm generally decreased with increase in UV dose. The typical Hertwig’s effect was observed after fertilized turbot eggs with UV-irradiated P. olivaceus sperm and the optimal UV dose for gynogenetic haploid production was 36,000 erg mm⁻². At 15°C, appropriate timing of cold shock for retention of the second polar body in turbot eggs was at 6 min after fertilization. Results of different combinations of two shock temperatures (1 or 3°C) and four shock durations (15, 25, 35 or 45 min) at 6 min after fertilization demonstrated that shock of 25 min at 1°C gave the highest production of diploid gynogens (39.58% relative to its diploid control). The results of this study reveal that the use of UV-irradiated P. olivaceus sperm for activation of turbot eggs and cold shock for polar body retention is an effective method to produce gynogenetic offspring.     

Reproductive biology of <Emphasis Type="Italic">Sillago aeolus</Emphasis> in Okinawa Island,Japan

ABSTRACT:   A total of 414 fish (female, 59.3–275.0 mm and male, 61.0–220.0 mm standard length) were collected from December 2000 to March 2002 around Okinawa Island, Japan, for the determination of sex, spawning season, maturity and fecundity. Monthly changes in the gonadosomatic index (GSI) exhibited similar trends for both sexes and the mean GSI maintained a high level between February and May. Furthermore, the percentage frequency of hydrated oocytes and the spermatozoic activity suggested that main spawning occurred between February and May. Some hydrated oocytes were found throughout the year, with a GSI value greater than 1.0, suggesting that sporadic spawning occurred. Length at first maturity was determined for females and males as 120 and 113 mm standard length, respectively. Almost 50% and 100% males were matured at the end of their 0 and 1 year of age group, respectively. In contrast, no females were found to be mature at 0+ age group, and almost 60% of females were mature at 1+ age group. At ages over 2 years, all males and females were found to be mature. Batch fecundity (BF) of 33 females was related to standard length, and the relationship between standard length and BF was expressed by the exponential equation: BF = 269.5e^0.020954SL.     

Age and growth of two gizzard shads, <Emphasis Type="Italic">Nematalosa come</Emphasis> and <Emphasis Type="Italic">N. japonica</Emphasis>, in coastal waters around Okinawa Island,southwestern Japan

The age and growth of two Nematalosa species around Okinawa Island were examined using sectioned otoliths collected from September 2003 to April 2006. Monthly changes in the frequency of the appearance of a translucent band on the outer margin of the otoliths indicated that ring formation occurred once a year from January to July for Nematalosa come and from January to March for Nematalosa japonica. The von Bertalanffy growth equations for both species were as follows: N. come: L _t  = 365.5{1 − exp[−0.111 × (t + 0.288)]} for females and L _t  = 214.7{1 − exp[−0.700 × (t – 1.110)]} for males; N. japonica: L _t  = 205.1{1 − exp[−1.068 × (t − 1.180)]} for females and L _t  = 195.5 {1 − exp[−1.293 × (t − 1.269)]} for males. The maximum ages observed for N. come and N. japonica were 11 and 6 years old, respectively. The growth of these species was characterized by the slow growth of N. come over many years, resulting in a larger size than N. japonica.     

Annual changes in distribution depths of bighand thornyhead <Emphasis Type="Italic">Sebastolobus macrochir</Emphasis> off the Pacific coast of northern Honshu,Japan

ABSTRACT:   Body size dependent distribution patterns of bighand thornyhead Sebastolobus macrochir were examined using bottom trawl surveys in the Tohoku area, off the Pacific coast of northern Honshu, Japan. In northern and southern Tohoku, distribution depths of ≤10-cm standard length (SL) fish increased from 500–600 m in 2003 to 600–700 m in 2005 with an increase in density of 11–20-cm SL fish at depths of 500–600 m. In 2004–2005, small fish (≤10 cm SL) were distributed in deeper waters than large fish (11–20 cm SL). In ≤20-cm SL fish, the main distribution depths changed from 300–600 m in 1997–2002 to 500–600 m in 2003 in southern Tohoku, but not in northern Tohoku. Stepwise multiple regression analysis showed that negative correlations were found in biomass densities between a few demersal fish species and bighand thornyhead at depths of 300–400 and 400–500 m in southern Tohoku. These results suggest that distribution of bighand thornyhead was affected by intra- and interspecific competitions in the Tohoku area.     

Reproductive cycle of yellow croaker <Emphasis Type="Italic">Larimichthys polyactis</Emphasis> in southern waters off Korea

The reproductive cycle and batch fecundity of yellow croaker Larimichthys polyactis were examined in 981 specimens (286 males, 695 females) caught from waters around Mokpo, Busan, and Jeju-do (Korea) between February 2008 and January 2009. Males and females with ripe-stage gonads were collected between April and June, at which time the mean gonadosomatic indices were also high, indicating that the spawning season of yellow croaker around the waters off southern Korea occurs from April to June. Degenerating postovulatory follicles as well as oocytes in the migratory-nucleus stage or hydrated stage were found in ripe-stage gonads, suggesting that this species can spawn repeatedly in a season. Batch fecundity in 45 females with migratory-nucleus or hydrated oocytes ranged from 19,396 to 106,311 eggs in fish varying from 20.0 to 26.7 cm in total length and was found to be positively related to total length and body weight. Our findings should assist in implementing a proper stock assessment of yellow croaker around the waters off Korea.     

Reproductive cycle of yellow sea bream <Emphasis Type="Italic">Dentex tumifrons</Emphasis> in Wakasa Bay,the Sea of Japan off central Honshu

ABSTRACT:   To determine the spawning season and reproductive cycle of the yellow sea bream, Dentex tumifrons , in Wakasa Bay, in the Sea of Japan off central Honshu, seasonal change in the gonadosomatic index ( GSI ) was examined and histological observations of both ovaries and testes were conducted. The female GSI gradually increased from May, maintained a high level between August and October and then rapidly decreased. The histological observations of the ovary showed that vitellogenesis began from May and developed until September. Spent fish began to be observed in October and all the fish collected in December were spent. There was only one peak in the seasonal change in GSI of males and females in Wakasa Bay. Thus, yellow sea bream spawn only in autumn in Wakasa Bay. Differences in the reproductive cycle and number of spawning seasons were found between the two different latitudinal areas, Wakasa Bay and the East China Sea (low latitudinal area) where the spawning seasons were spring and autumn. An increase in water temperature is an important factor to initiate gonadal maturation (recrudescence) and is terminated by the short day-length in Wakasa Bay.     

Monitoring of <Emphasis Type="Italic">Francisella noatunensis</Emphasis> subsp. <Emphasis Type="Italic">orientalis</Emphasis> in farmed Nile tilapia (<Emphasis Type="Italic">Oreochromis niloticus</Emphasis>) in Brazil

Francisella noatunensis orientalis is a bacterium that causes emerging bacteriosis in Nile tilapia (Oreochromis niloticus) in many parts of the world, including Brazil. It is a non-motile, Gram-negative, strictly aerobic, facultative intracellular coccobacillus. This species of bacteria is responsible for low to high mortality in fish farms, causing economic losses for fish farmers. This study aimed to detect the presence of F. noatunensis orientalis using qPCR (real-time polymerase chain reaction) and to describe lesions caused by the bacterium in O. niloticus in Brazilian aquaculture. For this purpose, 360 fish from six fish farms (30 per farm) were sampled at two time points (n = 180 per sampling). Necropsies and histopathology were performed for lesion observation, in addition to qPCR and sequencing for detection and identification of Francisella species. Environmental data were collected using a multiparameter sonde YSI EXO2. All measured limnological variables were within the optimum range for cultivation of Nile tilapia. The major lesions present were melanization of the skin, splenomegaly, granulomas, and inflammatory cell responses. The prevalence of francisellosis varied from 0 to 86.66% between time periods and fish farms analyzed, and an outbreak was observed during the second sampling period. This study describes the prevalence of francisellosis in O. niloticus and reports that the lesions found are not exclusively associated with this bacterial disease.     

Proteolytic digestive enzyme response in Japanese flounder larvae <Emphasis Type="Italic">Paralichthys olivaceus</Emphasis> fed two types of rotifers <Emphasis Type="Italic">Brachionus plicatilis</Emphasis> species complex

Two common live feeds, the Brachionus plicatilis species complex SS-type and L-type were used to assess whether there were any differences in protein hydrolysis and digestive trypsin activity in first feeding Japanese flounder. There were no significant differences in hydrolysis activity at 2, 3 and 7 days after hatching (DAH). At 5 DAH, hydrolysis activity was significantly higher in larvae fed SS-type (p?<?0.05) at 50 kDa in 1.5- and 3-h incubation whereas L-type treatment had not completely hydrolyzed the proteins after 3 h at the same molecular weight. Larvae fed SS-type had significantly higher (p?<?0.05) trypsin activity at 3, 5, 6, 7 DAH. Contribution of live prey to trypsin fraction in larvae showed significantly higher (p?<?0.05) fraction for SS-type at 5 DAH (2.18?±?0.44%) and 6 DAH (2.04?±?0.29%) and the effect of exogenous trypsin from live prey was relatively low when compared to the total trypsin activity in larvae. This study discusses the differences in ability to digest proteins in Japanese flounder when fed different rotifer morphotypes and highlights the adaptability of this species to alternative rotifer morphotypes during its early developmental stages.     

Value-per-recruit analysis of bighand thornyhead <Emphasis Type="Italic">Sebastolobus macrochir</Emphasis> caught off the Pacific coast of northern Honshu,Japan

The yield-per-recruit (YPR) analysis has been used to assess growth overfishing of exploited fish stocks. Since the ex-vessel price per weight widely depends on the size of the fish, the result of the YPR does not imply the revenue. The value-per-recruit (VPR) analysis, which is an economic expansion of the YPR analysis, was conducted for bighand thornyhead Sebastolobus macrochir caught off the Pacific coast of northern Honshu, Japan. The results showed that, for the current age at first capture (t _c = 3), the current fishing mortality (F = 0.12) was close to the optimum level. However, for the current F, optimum t _c in the VPR model was 8 years and would lead to a 47% increase compared to the current revenue. The maximum YPR was obtained at t _c = 6 years, but the revenue at t _c = 6 only gave a 20% increase in the maximum revenue. The difference was caused by the size dependency of the ex-vessel price per weight. The VPR model would generate fisheries management plans with both economical and biological consideration and would help in making general consensus of fisheries management strategies.     

Evaluation of different <Emphasis Type="Italic">Pyropia yezoensis</Emphasis> extracts as feed additives for growth and immunity of Japanese flounder <Emphasis Type="Italic">Paralichthys olivaceus</Emphasis>

We evaluated the effects of diets incorporating the red algae Pyropia yezoensis, prepared by several different extraction methods, on the growth of juvenile Japanese flounder Paralichthys olivaceus. We assessed growth performance, as well as the levels of amino acids, fatty acids, insulin-like growth factor I (IGF-I) and interleukins (ILs). Four experimental diets were developed based on different methods of processing P. yezoensis. A commercial feed, laver powder (P), high-pressure heat extraction of laver (HPHE) and acid hydrolysis extraction of laver were used as the experimental diets. Three experimental replicates were established for each diet (40 fish/group, body weight 123.7 ± 1.1 g), and the fish were fed for 6 weeks. We found no significant differences in weight gain, specific growth rate or feeding efficiency among the groups (P > 0.05); however, the fish fed HPHE had the greatest growth performance. Fish fed the laver extracts exhibited the highest protein efficiency ratio compared with the control and P groups. The experimental groups fed P. yezoensis extracts had significantly higher levels of IGF-I (P < 0.05) than those of the control group. High levels of IL-2 were found in the P and HPHE groups, IL-12 in the HPHE group, and IL-6 in all experimental groups. Therefore, these results suggest that a P. yezoensis extract improved the growth performance and immunity of Japanese flounder. In particular, the high-pressure heating process was a useful extraction method for preparing a P. yezoensis extract, which had beneficial effects as a dietary supplement in Japanese flounder.