Seasonal changes in oocyte size and maturity of the giant jellyfish, Nemopilema nomurai

To determine the reproductive season of the giant jellyfish Nemopilema nomurai, we investigated gonadal maturity in specimens collected from the East China Sea, Korea Strait, Wakasa Bay, and the Shonai Coast of Yamagata Prefecture. After the sex of the samples was determined, the long axis of at least 256 oocytes from each female was measured. In specimens collected from the coast of Japan in 2005 and in 2006, all gonads were sufficiently developed to determine sex. However, 18 of the 20 specimens from the East China Sea collected in July 2005 were immature, and sex could not be determined. The maximum and third quartile of oocyte length had a significant correlation with days elapsed from 30 June, but they were not related to bell diameter. Observations of gonad tissue sections of specimens collected in Wakasa Bay in 2006 confirmed that oocyte length was a good proxy for female maturity. Male maturity could also be determined. In conclusion, the sex of all of the small-sized medusae collected along the coast of Japan was determinable, and their gonads were at various stages of development up to fully mature. Therefore, the occurrence of small-sized jellyfish during the autumn in Wakasa Bay is not caused by recruitment of young population from the nearby coast.     

Evaluation of stock management procedures for walleye pollock in northern waters of the Sea of Japan using a simulation

To evaluate walleye pollock stock management procedures in the northern waters of the Sea of Japan, 30-year population dynamics, including uncertainties, were forecast. Errors in current stock size estimation, variability in future recruitment and changes in future fishing mortalities were incorporated. Results of virtual population analysis (VPA) from resampled catch-at-age data with bootstrap methods was used as the current stock size estimation with uncertainty. Performances of each scenario were evaluated using conservation, utilization, stability and reliability factors. Twenty-two management scenarios and continuing the current fishing mortality were evaluated. Scenarios with minor regulation changes and continuing the current fishing mortality showed poor stock conservation performances. Scenarios with minor regulation changes produced good short-term but poor long-term utilization. Stabilities were poor in continuing the current fishing mortality and fishing ban scenarios. Reliability in all scenarios after 30 years was smaller than in continuing the current fishing mortality; however, small differences among scenarios were observed. The simulation results indicated that multilateral assessment is needed to evaluate the management candidates. Uncertainty caused by recruitment variability mostly affected future population dynamics. The role of simulations in the production of effective scientific advice is discussed.     

Replacing the substitute—Guar meal as an alternative for non‐genetically modified soybean meal in the nutrition of rainbow trout (Oncorhynchus mykiss,Walbaum, 1792)

Soybean meal (SBM) is widely used in aqua feed products. In the European Union, only non‐genetically modified (non‐GM) SBM is accepted. However, global production of non‐GM soybeans is declining and is limiting its utilization in aqua feeds. Therefore, non‐GM SBM alternatives are required. In this study, guar meal was evaluated as a substitute for non‐GM SBM in test feeds for rainbow trout (Oncorhynchus mykiss). Fish (initial weight of 57 ± 10.1 g) were stocked to 12 experimental tanks of a freshwater recirculation system with a stocking density of 6 kg/tank (500 L). Fish were organized in triplicate groups and received isonitrogenous and isocaloric experimental feeds designated as control and test feeds 1–3, where 0, 50, 100 and 150 g/kg feed of non‐GM SBM was replaced by guar meal. During the experimental test period of 56 days, fish were fed twice a day until apparent satiation. Compared to the control group, daily feed intake of test feeds 1–3 was significantly increased by guar meal inclusion. No significant differences in feed conversion ratio and specific growth rate were detected among all the treatments. Furthermore, guar meal inclusion did not affect protein efficiency ratio. However, protein productive value was significantly impaired when guar meal incorporation was above 100 g/kg feed. In accordance with the affected protein productive value, the crude protein content of the proximate whole fish body declined significantly. In contrast, condition factor, hepatosomatic index, slaughter yield and fillet yield provided no significant differences between the experimental groups. In conclusion, this study demonstrated that non‐GM SBM could be entirely replaced by guar meal without affecting the general performance of fish and suggests guar meal as an appropriate alternative for non‐GM SBM in the nutrition of rainbow trout.     

Age estimation of the wild population of Japanese mantis shrimp <Emphasis Type="Italic">Oratosquilla oratoria</Emphasis> (Crustacea: Stomatopoda) in Tokyo Bay,Japan, using lipofuscin as an age marker

ABSTRACT:   In this study, the age composition of the Japanese mantis shrimp, Oratosquilla oratoria , in Tokyo Bay, central Japan, was investigated using lipofuscin, an autofluorescent pigment, as an age marker. Lipofuscin in a histological section of protocerebral bridge cell mass (PBCM) in the brain was identified by confocal microscopy, and its concentration was quantified by image analysis. Modal analysis of the lipofuscin concentration showed four regularly-spaced modes that could each be regarded as a distinct age group. This implied a constant lipofuscin accumulation in PBCM at a 6.5 × 10⁻²% volume fraction per year; it also implied the existence of individuals that are at least 4 years old. The lipofuscin concentration was found to be a more appropriate index than body length for estimating the age of O. oratoria , because the modal analysis on the body–length histogram failed to detect apparent age groups. This was probably a result of the declining growth rate with age and the individual variations in growth through molting leading to considerable overlap in the size between different age groups. The lipofuscin analysis suggested that fast-growing individuals in each cohort are recruited to the fishery, and most individuals attain the exploitable size between 2 and 3 years of age.     

Characterization of a monoclonal antibody against the 47- kDa antigen of Cryptobia salmositica Katz and its use in an antigen-capture enzyme-linked immunosorbent assay for detection of parasite antigen in infected rainbow trout, Oncorhynchus mykiss (Walbaum)

A monoclonal antibody (designated MAb-007) was produced against the pathogenic haemoflagellate Cryptobia salmositica Katz. This IgG3 antibody recognized the 47-kDa antigenic polypeptide of C. salmositica (SDS-PAGE and Western immuno-blotting). The antibody did not agglutinate live parasites, and there was no change in the staining intensity of the 47-kDa band on Western immunoblots after immunoabsorption of MAb-007 with live intact parasites. The 47-kDa antigen recognized by MAb-007 was localized in the cytoplasm of the parasite (immunogold labelling and electron microscopy). The monoclonal antibody cross- reacted with the 47-kDa polypeptides of C. bullocki Srrout and C. catostomi Bower & Woo. It was used in an antigen-capture ELISA for the detection of parasite antigen in the plasma of rainbow trout inoculated with the parasite, or with an attenuated vaccine strain of C. salmositica. All pre-infection plasma were negative while all infected fish with detectable parasitaemias were positive for antigen at 1–9 weeks after infection. Parasite antigen was even detected in vaccinated fish that were negative for parasites using the wet mount microscopic technique. The antigen-capture ELISA detected C, salmositica antigen in whole cell lysate preparations at concentrations as low as 0.5 μg ml^-1. Fifty microlitres of fish plasma was required in the antigen-capture ELISA, and the use of a plate reader and 96-well plates facilitated rapid analysis of a large number of plasma samples. The sensitivity of the assay makes it a potentially useful tool for detection of Cryptobia infections.