Reproduction related immunoglobulin changes in rainbow trout

Annual changes in plasma immunoglobulin (IgM) levels were investigated in three strains of rainbow trout Oncorhynchus mykiss which have different spawning periods, i.e., September–October, November–December, and January, reared under constant water temperature and natural day length. Plasma IgM levels decreased during the spawning season in all strains tested. The IgM changes became reversed in response to significant increases in plasma testosterone (T) and estradiol-17 in females and T and 11-ketotestosterone in males. Though the IgM decline showed a connection with suppressed immunocompetence, since many mature fish caught fungal diseases, no clear differences were observed in the plasma IgM levels between infected and noninfected fish during the spawning season. Incidentally, plasma IgM levels in infection prone fish were higher than in noninfection prone fish prior to the spawning season, whereas coincident differences in the plasma steroid levels were observed. Immature fish reared under lower water temperatures showed lower IgM levels. The effect of water temperature may have to be considered when analyzing the defense mechanism during the spawning season in rainbow trout.     

Genetic evaluation of interindividual relatedness for broodstock management of the rare species barfin flounder Verasper moseri using microsatellite DNA markers

ABSTRACT:   The barfin flounder has been recently declared to be rare, as the number of wild individuals in Japan has greatly reduced since 1975. The Japanese National Center for Stock Enhancement started the stocking program for this species on 1987. In the present study, microsatellite DNA loci were applied in order to determine the pedigree of the hatchery-produced juveniles for stock enhancement. Additionally, using six polymorphic microsatellite markers, the accuracy to assign dyads to categories of kinship was estimated using the relatedness estimator ( R _XY), similarity indexes (individual genetic identity [GI] and proportion of shared alleles [ P _S]), identification of kin groups using unweighted pair group method with arithmetic mean (UPGMA) clustering based on interindividual genetic distances (1- R _XY, 1- P _S, and 1-GI), a likelihood ratio approach, and partition methods to separate individuals into cohorts. The results were compared with the pedigree relationship previously obtained from parentage analysis. Estimation of the kinship relationship between individuals could be better inferred by means of UPGMA dendrogram clustering based on 1-GI or 1- P _S as interindividual genetic distances, or using computer software to perform partitioning of set of individuals.     

Supplemental effect of bile salts to soybean meal-based diet on growth and feed utilization of rainbow trout <Emphasis Type="Italic">Oncorhynchus mykiss</Emphasis>

A feeding experiment was conducted to evaluate the supplemental effect of bile salts to a defatted soybean meal-based non-fish meal diet for rainbow trout Oncorhynchus mykiss. A fish meal-based diet (FM) and two non-fish meal diets with and without bovine bile salts (SC+B and SC, respectively) were fed to fish (13 g initial weight) for 10 weeks. Fish fed diet SC showed inferior growth and feed efficiency, while bile salt supplementation improved the parameters to the same levels as fish fed diet FM. Crude fat and starch digestibility of diet SC-fed fish decreased after the 10-week feeding trial compared to the data obtained with fish that had no experience of the diet. Total biliary bile salt content and intestinal maltase activity of fish fed diet SC were the lowest among treatments, while these parameters were improved by bile salt supplementation. Morphological changes occurred in the distal intestine and liver of the diet SC group, although the histological features of fish fed diet SC+B were similar to those of fish fed diet FM. These results suggest that bile salt supplementation to a soybean meal-based diet improves the nutrient utilization by normalizing digestive processes in rainbow trout.     

Estimating and monitoring the stock size of sandfish <Emphasis Type="Italic">Arctoscopus japonicus</Emphasis> in the northern Sea of Japan

ABSTRACT:   The stock size of sandfish in the northern Sea of Japan was estimated by a virtual population analysis (VPA) and sensitivity analyses were attempted on the VPA estimate. The stock size estimates were approximately 600–900 million until 1975, but since 1976 they have rapidly decreased. In the sensitivity analyses, the estimates of absolute stock size were not sensitive against the changes in the fishing mortality coefficient for terminal age and the measurement error in catch-at-age. This suggested that the relative stock size remains almost unaffected by the error in the data used in the VPA, if the degree of catch-at-age error and the natural mortality coefficient is correct. The relationships between the biomass estimated by the VPA and the density index from Danish seine fisheries, and between the biomass and the catch per unit effort (CPUE) from the experimental survey using Danish seine nets, were also examined. The density index and the CPUE indicated significant relations with the biomass. Consequently, the CPUE is useful to monitor the relative stock size in a timely manner, and the VPA estimate and the CPUE should be utilized for adjusting the total allowable catch in the multiseasons.     

Models for forecasting sandfish catch in the coastal waters off Akita Prefecture and the evaluation of the effect of a 3-year fishery closure

SUMMARY: The sandfish Arctoscopus japonicus in the coastal waters off Akita Prefecture had been landed in amounts of more than 10 000 t continuously from 1963 to 1975. From 1976, however, it began to decrease sharply and fell to only 74 t in 1984. The fishery society of Akita Prefecture closed the fishing from 1 September 1992 to 30 September 1995. Since 1995, the total allowable catch (TAC) allocated in each year has increased. However, the mechanism behind the increment of catch has not been clearly demonstrated. The aim of this study is to elucidate the mechanism behind the increase of catch using catch forecasting models constructed with past water temperature and catch data. The results were as follows: (i) the effect of water temperature in the depth strata 200–300 m, September of year t –1, t –2 and t –3 of station 1 would be important for forecasting the catch in year t; (ii) coastal catch in year t –1 and t –2 would be important for forecasting the catch in year t; (iii) the effect of a fishery closure would be significantly related to the period of the closure and the environmental condition such as water temperature; and (iv) the TAC system would be important for the recovery of stock and to avoid the depletion of abundance.     

Hypoxic conditions induce centrum defects in red sea bream Pagrus major (Temminck and Schlegel)

A previous study elucidated that an extreme hypoxia during somitogenesis induced the most frequent skeletal malformation centrum defects in red sea bream (RSB), Pagrus major. In this study, details of the hypoxic conditions to induce them in RSB, dissolved oxygen (DO) concentration and exposure time to hypoxia, were investigated. Fertilized eggs were exposed to seawater of six DO concentrations (0%, 10%, 25%, 50%, 75% and 100% of saturation) for seven different periods (5, 10, 30, 60, 120, 240 and 360 min) during somitogenesis. Somitic disturbances in newly hatched larvae were induced by exposure to 0% and 10% DO concentration for 10 and 120 min and longer respectively. Rearing eggs exposed to hypoxic condition of 10% DO for 240 min for 40 days post‐hatch showed that the location and the frequency of somitic disturbances in larvae and centrum defects in juveniles were significantly correlated (P<0.01). Dissolved oxygen concentration of the interstitial water in the egg high density layer formed at the water surface in a stationary state abruptly decreased to 3.7% within 7 min. Centrum defect induction by exposure of eggs to extreme low DO concentrations for a short period, which is the probable situation in the practical juvenile production, suggests that careful maintenance of DO concentration is important in the incubating water of fertilized eggs during egg sorting and transportation, where eggs are made into a pile and undergo hypoxia, for the prevention of centrum defects.     

Diurnal rhythm of steroid biosynthesis in the testis of terminal phase male of protogynous wrasse, Pseudolabrus sieboldi, a daily spawner

The wrasse, Pseudolabrus sieboldi, is a diandric protogynous labrid fish. Spawning is performed by a terminal phase (TP) male and an initial phase (IP) female between 6:00 and 9:00 h daily during two-month-long spawning season. In the present study, to investigate the roles of steroid hormones in the diurnal spermatogenesis of the P. sieboldi TP male, all steroid hormones produced in the testis were identified and the synthetic pathways of these steroids were determined. Furthermore, the circulating levels of the major steroids produced were analyzed throughout a day at 3-hour intervals during spawning season. In the testis, 11-ketotestosterone (11-KT), estradiol-17β (E2), 17,20β-dihydoxy-4-pregnane-3-one (17,20β-P) and 17,20β,21-trihydroxy-4-pregnen-3-one (20β-S) were synthesized as the major metabolites. In vitro steroid biosynthesis experiments showed similar results to the circulation profiles of the major steroids. This study is the first to clarify the complete steroidogenic pathways in the gonads of a diandric protogynous species throughout its life, when combined with the results of the steroidogenesis in the ovarian follicles. This is also the first report of a clear diurnal rhythm of the steroid production corresponding to the spermatogenic process in the testis of a male teleost.     

Oxygen deficiency during somitogenesis causes centrum defects in red sea bream, Pagrus major (Temminck et Schlegel)

Vertebral deformities in red sea bream, Pagrus major, remain serious obstacles to the improvement of seedling quality for its aquaculture. However, the causalities of the deformities remain unclear and prevention methods have not yet been established. In this paper, oxygen deficiency during somitogenesis was demonstrated to cause centrum defects (formerly called fused vertebrae in many cases), which are the major vertebral deformity in cultured red sea bream. An induction experiment of centrum defects was conducted by placing fertilized red sea bream eggs under low dissolved oxygen conditions (10.3–16.6%). The low oxygen treatment was carried out for five different developmental stages of embryo: two‐cell stage to blastula stage; gastrula stage; three to 10 somites stage; 11–17 somites stage and 18–24 somites stage. Oxygen deficiency during somitogenesis induced a high incidence of centrum defects. In contrast, it hardly induced centrum defects during the other stages. The dissolved oxygen concentration in the rearing water should be carefully regulated for fertilized eggs, especially during somitogenesis to reduce the incidence of vertebral deformities in the red sea bream.     

Spatial variation of local stand structure in an Abies forest, 45 years after a large disturbance by the Isewan typhoon

Heterogeneity of forest stand structure often results from repeated small disturbances, but structural variation also arises in a stand that has regenerated after a single large stand-replacing disturbance. We explored the structural variation within a subalpine Abies forest in Japan that regenerated after a large typhoon in 1959. In 2004, four 50 × 50 m plots were established at two sites in the regenerated forest. To characterize local stand structure within each plot, we determined the stem density, stand basal area, mean diameter at breast height (DBH), and coefficient of variation (CV) of DBH in 10 × 10 m subplots. We analyzed the spatial distribution pattern of the trees in each subplot using the L(t) function and categorized the distributions as clumped or non-clumped. The analysis revealed marked variation among subplots in the stand’s structural characteristics. Although the spatial distribution patterns of the trees in all plots were clumped, 11 of 50 subplots at one site and 39 of 50 subplots at the other site were non-clumped. Subplots with a clumped distribution pattern generally had a smaller basal area, smaller mean DBH, and greater CV of DBH than subplots with the same density but a non-clumped pattern. These results illustrated the spatial heterogeneity of forest structure that can arise in Abies forest that has experienced a large disturbance, probably because of the different densities and distribution of saplings surviving the disturbance and the different forest growth dynamics that result.