Analysis of food preference and competition based on stomach contents of fish species inhabiting fresh and brackish waters in South Korea

We analysed the stomach contents of fish species inhabiting fresh and brackish waters of South Korea to improve our understanding of feeding preferences and competition among them. The stomach contents of 54 fish species contained 237 genera, 187 families, 84 orders, 37 classes and 25 phyla. Faunal food items included 164 genera, 129 families, 47 orders, 23 classes and 16 phyla. Floral food items were relatively limited, comprising 73 genera, 58 families, 37 orders, 14 classes and nine phyla. The most consumed faunal food item was Chironomidae (Diptera), whereas the most consumed floral food item was Fragilariaceae (Fragilariales). The 54 fish species were classified into six groups using hierarchical and nonmetric multidimensional analysis based on their food preferences: Group 1 (G1) fishes were zooplanktivores; group 2 (G2) fishes mainly consumed Malacostraca, Maxillopoda and other fishes (e.g. Osmeriformes); groups 3 (G3) and 4 (G4) consumed Chlorophyta, Cyanobacteria and Bacillariophyta; and groups 5 (G5) and 6 (G6) consumed macroinvertebrates. Network analysis was used to link fishes with their food items. The highest hub score for food items was for macroinvertebrates, including Diptera (13.9), Ephemeroptera (11.1) and Trichoptera (8.2). Niche breadth analysis represented the diversity of food items among the feeding groups (G1–G6). Food item diversity was high for planktivores (G1 and G3) and omnivores (G4). Conversely, the dietary diversity of carnivores (G2) and insectivores (G5) was limited. Competitive relationships between fishes, as represented by the niche overlap in G5 (insectivores), were higher than those between other groups.     

Increase in estrogen signaling in the early brain of orange-spotted grouper Epinephelus coioides: a mini-review

Despite neurosteroidogenic enzymes are playing important roles in the regulation of brain development and function, the potential link between brain and gonad by the action of steroid hormones during gonadal sex differentiation is still not clear in teleosts. In this mini-review, we summarized our understanding on the early brain development related to the synthesis of neurosteroids and receptor signaling during gonadal sex differentiation in protogynous orange-spotted grouper, Epinephelus coioides (functional females for the first 6 years of life and start to sex change around the age of 7 years) and protandrous black porgy (functional males for the first 2 years of life but begin to change sex during the third year). We found a similar profile in the increased expression of brain aromatase gene (aromatatse B or cyp19a1b), aromatase activity, estradiol (E₂), and estrogen signaling in the brain of both grouper and black porgy fish during gonadal sex differentiation. In contrast to mammals, teleost fish Cyp19a1b expressed in a unique cell type, a radial glial cell, which is acted as progenitors in the brain of developing and adult fish. In agreement with these pioneer studies, we demonstrated that the grouper cyp19a1b/Cyp19a1b was expressed in radial glial cells. Further, in vivo data in the grouper brain showed that exogenous E₂ upregulated Cyp19a1b immunoreactivity (ir) in radial glial cells. These data suggest the possible roles of Cyp19a1b and E₂ in early brain development which is presumably related to gonadal sex differentiation.     

油菜蚤跳(虫甲)生物学特性研究

通过室内饲养和田间调查，较系统地研究了油菜蚤跳甲的生活史，各虫态发育历期，成，幼虫习性及发生与油菜播期，种植方式，油菜品种，类型，土壤质地等条件的关系，首次报道了油菜蚤跳甲成虫秋季交配产卵习性及在室内部分孵化现象。     

An ecosystem-based assessment of the Korean blue crab trammel net fishery in the Yellow Sea and management implications

Landings in the blue crab, Portunus trituberculatus, fishery in Korean waters of the Yellow Sea have declined substantially from 11,000 t in the 1980s to 2,300 t in 2004. Blue crab habitat quality in the Yellow Sea has been degraded by anthropogenic activities including sand mining, land reclamation, and coastal pollution. Various traditional management measures have been implemented, including closed seasons during spawning and size limits, but these measures alone have been unsuccessful to conserve blue crab stocks. Consequently, a total allowable catch and a stock-rebuilding program using an ecosystem-based management approach were implemented in 2003 and 2006, respectively to rebuild blue crab stocks and restore habitats. This program involved assessment of both blue crab stock status and trammel-net fishery impacts at an ecosystem-level using an ecosystem-based fisheries assessment method ( [Zhang et al., 2009] and [Zhang et al., 2010]), which considered fishery data from catch and effort time-series, crab population biology, and ecosystem characteristics, including habitats and environmental conditions. Recent (2008) management status indices have shown significant positive change compared to conditions in 2000 with respect to sustainability of the stock and fishery and with regards to biodiversity and ecosystem habitat quality.     

小窑湾浮筏养殖区底质沉积物初步研究

20 0 0年 10月对小窑湾底质沉积物进行了 10个项目的海上调查 ,结果表明 :小窑湾底质重金属含量均为国家一类标准 ,符合渔业生产条件 ;硫化物、有机质含量虽然为国家一类标准 ,但已趋于上限 ,说明底质已被污染 ;油类已达国家二类标准 ,超出了渔业生产的许可范围 ;底质沉积物中每天向海水中释放的氮为 12 936mg/(m2 ·d) ,释放的磷为 0 4 95mg/ (m2 ·d)。     

三种扇贝种间血液生理指标比较及热胁迫对栉孔扇贝血液生理指标的影响

为了比较3种扇贝血液中的K⁺、Na⁺、Ca²⁺和Cl^-浓度,血氧(pO₂)和血二氧化碳(pCO₂)气体分压及血液酸碱度(pH)的差异情况,实验利用血气分析仪对栉孔扇贝、虾夷扇贝和海湾扇贝的血液生理指标进行测定。结果显示,扇贝的血液生理指标呈现显著的物种差异,其中栉孔扇贝血液的K+浓度[(15.74±1.47) mmol/L]、Na+浓度[(388.07±11.38)mmol/L]、Cl-浓度[(462.43±6.88) mmol/L]和p O2[(140.13±15.35) mmHg]最高。此外,栉孔扇贝和虾夷扇贝的Ca²⁺浓度和pCO₂含量较高,而海湾扇贝的pH最高。对相同月龄不同大小栉孔扇贝血液指标进行比较,发现栉孔扇贝的血液pH值与其壳高呈正相关(r=0.611),而生理指标与壳高呈负相关。随着温度的升高,栉孔扇贝血液的Ca²⁺浓度显著增加,而pO₂显著下降,K<...     

Cloning, tissue distribution and hormonal regulation of stearoyl-CoA desaturase in tilapia, Oreochromis mossambicus

The stearoyl-CoA desaturase cDNA in tilapia (Oreochromis mossambicus) was cloned by RT-PCR and RACE, and it was compared with those in grass carp, common carp and milkfish. Nucleotide sequence analysis revealed that the full length of cDNA (1172 bp) clone encompasses 1008 bp open reading frame (ORF) encoding 336 amino acid residues. The deduced amino acid sequence shares 78–82% identity with the teleosts and 64–66% with mammals compared, and like these fish, the cloned tilapia stearoyl-CoA desaturase amino acid sequence conserves three histidine cluster motifs (one HXXXXH and two HXXHH), which functioned as non-heme iron binding sites, essential for stearoyl-CoA desaturase activity. RT-PCR and Northern blot analysis reveal that tilapia stearoyl-CoA desaturase is expressed only in liver, but the stearoyl-CoA desaturase expression in multiple tissues was observed in milkfish, grass carp and carp. Further, the hormonal regulation of stearoyl-CoA desaturase gene expression was investigated by a single injection of 17β-estradiol and testosterone. The results showed that the administration of 17β-estradiol to tilapia led to a greater increase in desaturase activity than testosterone, and higher doses of steroids produced greater increases in enzyme activity. The comparative RT-PCR analysis showed that the stearoyl-CoA desaturase mRNA level increased significantly in 17β-estradiol treated animals, especially in the groups receiving a single injection of 50 mg 17β-estradiol. This was reflected in the decrease in the saturated fatty acids and the increase in the monounsaturated fatty acids. The proportion of the polyunsaturated fatty acids was not affected.     

Establishment,characterization, virus susceptibility and transfection of cell lines from cobia,Rachycentron canadum (L.), brain and fin

Establishment and characterization of two cobia, Rachycentron canadum, cell lines derived from cobia brain (CB) and cobia fin (CF) are described. Caudal fin and brain from juvenile cobia were dissociated for 30 and 10 min, respectively, in phosphate‐buffered saline containing 0.25% trypsin at 25 °C. The optimal culture condition for both dissociated cells (primary cell culture) was at 28 °C in Leibovitz‐15 medium containing 10% foetal bovine serum. The cells have been sub‐cultured at a ratio of 1:2 for more than 160 passages over a period of 3 years. Origin of the cultured cells was verified by comparison of their sequences of mitochondrial cytochrome oxidase subunit I genes (cox I) with the cox 1 sequence from cobia muscle tissue. The cell lines showed polyploidy. No mycoplasma contamination was detected. Susceptibility to grouper iridovirus was observed for the CB cell line but not the CF cell line. Both cell lines expressed green fluorescent protein after being transfected with green fluorescent reporter gene driven by the cytomegalovirus promoter.     

Effects of temperature and dietary protein on the growth performance and IGF‐I mRNA expression of juvenile mirror carp (Cyprinus carpio)

Juvenile mirror carp were fed with five different diets containing 303, 322, 341, 361 and 379 g kg^?1 protein and reared at three different water temperatures (18, 23 and 28 °C) for 60 days. We investigated the insulin‐like growth factor I (IGF‐I) mRNA expression, growth performance and the relationship between IGF‐I mRNA expression and the growth performance. The results indicated that the IGF‐I mRNA expression, final body weight, specific growth rate (SGR) and feed efficiency (FE) were enhanced significantly with increasing dietary protein levels (P < 0.05), whereas the protein efficiency ratio, hepatosomatic index (HSI) and viscerosomatic index (VSI) were decreased. Moreover, the IGF‐I mRNA expression, final body weight and SGR were increased significantly with temperature, whereas the HSI and VSI indices were decreased significantly with temperature. Correlation analysis showed that the IGF‐I mRNA expression levels in the brain and liver were positively related to the SGR and FE growth indices (P < 0.01). Finally, the optimal protein requirements for fish growth in different seasons were determined based on the values of SGR and FE, that is 343–348 g kg^?1 protein at 18 °C, 354–352 g kg^?1 at 23 °C and 371–362 g kg^?1 at 28 °C. In this way, we can adjust the dietary protein levels according to culture temperature to reduce any negative impacts on dietary costs and environmental pollution.