Comparative analysis of using cereal grains and compound feed in semi-intensive common carp pond production

The semi-intensive system of carp farming is dominant in inland aquaculture. Although it appears to be simple, this system has a whole range of options, from those based on traditional rearing methods with use of plants from the region where the fish are reared to production based on the use of high-quality concentrated feeds. In this paper, we conduct a comparative analysis of the effect of using cereal grains as opposed to compound feed (pelleted and extruded) on the quantity of fish produced, flesh quality, histological changes in the digestive tract, water quality, and structure of the biocoenosis in the pond ecosystem. When the fish are fed cereal grains, production ranges from 500 to 1500 kg/ha, while using compound feed gives production that is twice as great. The proportions of protein and water are higher and that of lipids lower in flesh of common carp reared on compound feed in relation to fish fed cereal grains. Use of extruded feed gives better content of n-3 polyunsaturated fatty acids and a better n-3/n-6 ratio than when pelleted feed and cereal grains are used. Comparison of water quality in carp ponds under conditions of using various types of feed indicates that there are no significant differences. Although it was expected that feed with a higher percentage of proteins would cause disturbances in the aquatic ecosystem, their continual incorporation into the cycling of matter in the water contributes to maintenance of ecological equilibrium and even indirectly promotes growth of the common carp.     

Post-molt processes of cuticle formation and calcification in the Japanese mitten crab <Emphasis Type="Italic">Eriocheir japonicus</Emphasis>

This study examines the following in the Japanese mitten crab: (1) the structure of the exoskeleton with special reference to its calcification; (2) the progression of post-molt cuticle formation and calcification. In the crab, the structure and calcification state of the exoskeleton at the molt and during the inter-molt stage were similar to those of other crustaceans. During the inter-molt, the exoskeleton consisted of four cuticle layers; the outermost epicuticle, the exocuticle, the endocuticle and the innermost membrane layer. Intense calcification was observed in the exo- and endocuticle. At the molt, the synthesis of the epi- and exocuticle was already complete, and the addition of the endocuticle began after the molt. Calcification of the exocuticle initiated soon after the molt, but there was a delay between endocuticle matrix synthesis and calcification. Histology showed that the process of calcification was similar to that in other crustaceans. However, calcium concentrations within the exoskeleton continued to increase and never reached the levels of the inter-molt stage at the end of the experiment. This suggests that the Japanese mitten crab is relatively slow to calcify compared to other crustaceans.     

Relative potencies of natural estrogens on vitellogenin and choriogenin levels in the Indian freshwater spotted snakehead, <Emphasis Type="Italic">Channa punctata</Emphasis>: in vivo and in vitro studies

The relative efficacies of three natural estrogens viz., estrone (E₁), estradiol-17β (E₂) and estriol (E₃) to induce synthesis of vitellogenin (Vg) and choriogenin (Chg) were assessed in primary hepatocyte cultures of the Indian freshwater spotted snakehead, Channa punctata. Hepatocytes were isolated from the spotted snakehead liver by a non-enzymatic protocol. Optimum culture conditions were standardized for ensuring their viability and functioning. Isolated hepatocytes were cultured for 48 h for monolayer formation and then exposed to various concentrations (0.001–10 μM) of the three estrogens. Competitive homologous ELISAs, developed and validated for spotted snakehead Vg and Chg were employed to determine the amounts of these two proteins secreted into the culture medium after 48 h of incubation. The results reveal that although all the three estrogens were effective in inducing the production of Vg and Chg in a dose-dependent manner, there were differences in their relative potencies. Of three estrogens, E₁ was the least potent and could induce synthesis of Vg and Chg only at a minimum concentration of 0.5 μM; whereas significant levels of both the proteins were quantified in culture medium by exposing the hepatocytes to E₂ or E₃ even at a concentration of 0.001 μM. All three estrogens were effective in inducing synthesis of Vg and Chg in vivo also. These results suggest the possibility of employing the above in vitro experimental design to monitor the presence of estrogens/estrogen-like chemicals in natural waters, which could interfere with the estrogen receptor system of fish. This study further points to the possibility of using Chg, in addition to Vg, as a parameter for screening various chemicals for their estrogenic activity.     

Guanine-cytosine contents of the host and symbiont cDNA in a symbiotic coral

ABSTRACT:   Hermatypic (reef-building) corals harbor dinoflagellate endo-symbionts Symbiodinium spp. In studying gene expression in such symbiotic corals, problems arise regarding how to distinguish the coral and symbiont mRNA, and how to estimate their fractions in the mRNA population of the holobiont (symbiotic complex of the coral and Symbiodinium cells). In this study, these issues were addressed using juveniles of hermatypic coral Acropora tenuis in symbiosis with Symbiodinium cells of strain PL-TS-1. First, the guanine-cytosine (GC) contents were determined in expressed sequence tags (EST) from PL-TS-1 cells cultured in vitro and symbiont-free larvae of A. tenuis , and their average GC contents were found to be significantly different. The average GC content of the EST from the holobiont was much closer to that of A. tenuis larvae, suggesting that the majority (>90%) of mRNA isolated from the holobiont originated in the host. In protein-coding sequences, little overlap was observed between the GC-content distributions of PL-TS-1 cells and A. tenuis larvae. All of the coding sequences ( n  = 59) found in the A. tenuis EST had GC contents below 0.5, whereas the GC content exceeded 0.5 in the majority (43/44) of coding sequences from the nuclear genome of PL-TS-1 cells.     

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.     

Microsatellite marker isolation and cultured strain identification in <Emphasis Type="Italic">Carassius auratus gibelio</Emphasis>

Microsatellites have become the preferred molecular markers for strain selection and genetic breeding in fish. In this study a total of 105 microsatellites were isolated and identified in gibel carp (Carassius auratus gibelio) by microsatellite sequence searches in GenBank and other databases and by screening and sequencing of positive clones from the genomic library enriched for AG and GATA repeats. Moreover, nineteen microsatellites were randomly selected to design locus-specific primer pairs, and these were successfully used to identify and discriminate different cultured strains of gibel carp including strains A, D, L, and F. Three different types of microsatellite pattern were distinguished by the number and length of fragments amplified from the 19 primer pairs, and some microsatellite primer pairs were found to produce different microsatellite patterns among strains and strain-specific fragments. In addition, some duplicated alleles were also detected in two microsatellite patterns. Therefore, the current study provides direct molecular markers to discriminate among different cultured strains for selective breeding and aquaculture practice of gibel carp.     

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.     

Relationship between zooplankton abundance and the early marine life history of juvenile chum salmon <Emphasis Type="Italic">Oncorhynchus keta</Emphasis> in eastern Hokkaido,Japan

Interannual variations in abundance, timing of outmigration from rivers, growth rate and condition of juvenile chum salmon (Oncorhynchus keta) were studied in the Nemuro Strait (eastern Hokkaido, Japan) during 1999–2002 to establish a possible relationship to zooplankton abundance. The otolith microstructure of juveniles was examined each year in late June to determine their time and size at sea entry (i.e., outmigration), and to estimate the early marine growth rates. Salmon outmigration peaked in mid- or late May, which coincided, in three of the four study years, with the peak release of juveniles into rivers within the study area. Abundance, growth rate and condition of fish were higher in 2001, when—compared to other years—smaller fish experienced higher growth rates, coinciding with greater zooplankton abundance for that year. Our results suggest that high zooplankton abundance positively influenced juvenile chum salmon growth and the condition of the fish during their early marine life despite their small size at sea entry.     

Development of an in vitro culture system for producing eel larvae from immature ovarian follicles in Japanese eel <Emphasis Type="Italic">Anguilla japonica</Emphasis>

To standardize conditions during the final maturation and ovulation of ovarian follicles from Japanese eel, we have developed a culture system for the production of fertilizable eggs from post-vitellogenic ovarian follicles in vitro. Post-vitellogenic ovarian follicles were incubated in culture medium supplemented with 17α,20β-dihydroxy-4-pregnen-3-one (DHP) with or without bovine serum albumin (BSA) to assess the effects of protein concentration. Eggs that ovulated during incubation were fertilized, and the remaining follicles were incubated in prostaglandin F_2α (PGF_2α) for a further 3 or 6 h before fertilization. Male eels were injected repeatedly with human chorionic gonadotropin. The quality of eggs obtained under the different culture conditions was evaluated after artificial fertilization in terms of hatching success. Hatching rates tended to decrease with increasing concentrations of BSA in the incubation medium in a dose-dependent manner. The addition of PGF_2α drastically increased the number of eggs that ovulated, but the rate of hatching was greatly decreased compared with eggs obtained earlier by DHP incubation alone. The larvae obtained from artificially fertilized eggs produced in vitro survived for 14 days without feeding. We conclude that in vitro culture systems thus have a great potential for the acquisition of good quality eggs under tightly controlled artificial conditions, culminating in the production of eel larvae.