Development of nursery culture techniques for the mud crab Scylla paramamosain (Estampador)

Cannibalism is one of the main causes of mortality in the culture of the mud crab Scylla paramamosain, particularly in the early post‐larval and juvenile stages when the densities of hatchery‐reared crabs may be very high before stocking into ponds or release into the wild for stock enhancement. In a series of experiments investigating cannibalism mitigation, the influence of stocking density, the effectiveness of sand substrate, brick and shell shelters and feed type were compared in culture of crabs from instar 1 for short nursery periods of 15–30 days. Inclusion of brick and shell shelters significantly increased survival over sand substrate alone. However, inclusion of shelters did not affect growth rates. In scaled‐up nursery production in lined‐ponds, with shelters, live Artemia biomass and fresh chopped shrimp or tilapia were found to be equally effective feeds for juvenile crabs stocked at a density of 70 m⁻² from instar 1 and grown for 30 days [52–66% survival, 21.6–24.6 mm carapace width (CW)]. In an extended nursery period for a further 30 days, crabs of 22 mm CW, stocked at 30 m⁻² in the same ponds, attained a final size of 34.5–36.2 mm CW with a survival of 64.3–67.0% using the same feeds.     

Atlantic coast feeding habits of striped bass: a synthesis supporting a coast-wide understanding of trophic biology

The recent increase in the Atlantic coast population of striped bass, Morone saxatilis (Walbaum), prompted managers to re‐evaluate their predatory impact. Published and unpublished diet data for striped bass on the Atlantic Coast of North America were examined for geographical, ontogenetic and seasonal patterns in the diet and to assess diet for this species. Diets of young‐of‐the‐year (YOY) striped bass were similar across the Upper Atlantic (UPATL), Chesapeake and Delaware Bays (CBDEL) and North Carolina (NCARO) areas of the Atlantic coast where either fish or mysid shrimp dominate the diet. For age one and older striped bass, cluster analysis partitioned diets based on predominance of either Atlantic menhaden, Brevoortia tyrannus (Latrobe), characteristic of striped bass from the CBDEL and NCARO regions, or non‐menhaden fishes or invertebrates, characteristic of fish from the UPATL, in the diet. The predominance of invertebrates in the diets of striped bass in the UPATL region can be attributed to the absence of several important species groups in Northern waters, particularly sciaenid fishes, and to the sporadic occurrences of Atlantic menhaden to UPATL waters. In all regions, across most seasons and in most size classes of striped bass, the clupeiod fishes; menhaden, anchovies (Anchoa spp.) and river herrings (Alosa spp,) and Atlantic herring, Clupea harengus L., dominated the diets of striped bass above the first year of life.     

Stocking density and artificial habitat influence stock structure and yield from intensive nursery systems for mud crabs Scylla serrata (Forsskål 1775)

Intensive nursery systems are designed to culture mud crab postlarvae through a critical phase in preparation for stocking into growout systems. This study investigated the influence of stocking density and provision of artificial habitat on the yield of a cage culture system. For each of three batches of postlarvae, survival, growth and claw loss were assessed after each of three nursery phases ending at crab instars C1/C2, C4/C5 and C7/C8. Survival through the first phase was highly variable among batches with a maximum survival of 80% from megalops to a mean crab instar of 1.5. Stocking density between 625 and 2300 m⁻² did not influence survival or growth in this first phase. Stocking densities tested in phases 2 and 3 were 62.5, 125 and 250 m⁻². At the end of phases 2 and 3, there were five instar stages present, representing a more than 20‐fold size disparity within the populations. Survival became increasingly density‐sensitive following the first phase, with higher densities resulting in significantly lower survival (phase 2: 63% vs. 79%; phase 3: 57% vs. 64%). The addition of artificial habitat in the form of pleated netting significantly improved survival at all densities. The mean instar attained by the end of phase 2 was significantly larger at a lower stocking density and without artificial habitat. No significant effect of density or habitat on harvest size was detected in phase 3. The highest incidence of claw loss was 36% but was reduced by lowering stocking densities and addition of habitat. For intensive commercial production, yield can be significantly increased by addition of a simple net structure but rapidly decreases the longer crablets remain in the nursery.     

池养条件下革胡子鲶仔幼鱼摄食习性与生长的初步研究

本文报道了在人工饲养条件下革胡子鲶仔幼鱼的摄食习性和生长的研究结果。仔鱼孵出2或3日,尚残存卵黄囊时即行开口摄食。仔鱼适口的开食饵料是轮虫,随着鱼体的生长,摄食枝角类、桡足类和摇蚊幼虫的比例迅速增加。幼鱼昼夜摄食强度有一定的节律,夜间18:00～22:00时摄食强度最大。经测量和数理统计分析,确定革胡子鲶仔幼鱼的全长与日龄呈直线关系,体重与日龄和全长对体重的关系均为幂函数关系,并计算出它们相应的回归方程式。     

Is batch variability in hatching time related to size heterogeneity and cannibalism in pikeperch (Sander lucioperca)?

Larval size heterogeneity is known to induce cannibalism, and procedures to avoid larval size differences are consequently implemented already during egg incubation and hatching. We investigated the relation between larval development variability, size heterogeneity and cannibalism in pikeperch. Larvae were sorted into five groups according to the time of hatching during a 65‐h period. The larvae with different times of hatch were then reared separately or together during an 18‐day period. Late hatched larvae were longer (P=0.003) and had less yolk remaining (P<0.001) than early hatched individuals at the time of hatching. However, on 11 days post fertilization, the late‐hatching larvae tended to have larger yolk reserves than earlier hatched individuals (P=0.07). Furthermore, the next day, a lower proportion in the late fraction had switched to exogenous feeding (P=0.024). That larvae with a late hatching time developed slower suggests a positive relationship between the hatching time and the embryonic developmental rate. However, differences in the length and available yolk reserves at hatching between larval fractions with different hatching times suggest that hatching is not strictly associated with a specific developmental stage, and that factors other than the development rate of the embryo are involved in the timing of hatching.     

杂交鳢和乌鳢池塘养殖对比试验

对杂交鳢和乌鳢进行池塘养殖对比试验.前者投喂人工饲料,后者投喂冰鲜鱼,结合水质调控和病害防治等技术,杂交鳢成活率80.9%,乌鳢53.9%;杂交鳢平均单产为5.2 kg/m~2,饵料系数1.367;乌鳢1.8 kg/m~2,饵料系数4.29.整个养殖过程杂交鳢塘换水2次,乌鳢塘换水6次.     

The prevalence of mycobacterial infections in striped bass in Chesapeake Bay

Several species of bacteria have been isolated from diseased striped bass, Morone saxatilis (Walbaum), in Chesapeake Bay. Mycobacteria species are of particular interest because of their association with chronic lesions in both fish and humans. The resulting disease in fish may be characterised by emaciation, inflammation of the skin, exophthalmia (pop‐eye), ascites (dropsy), open lesions, and ulceration. The prevalence of mycobacterial infection in 217 striped bass in the Maryland portion of Chesapeake Bay was determined to provide evidence of decreased overall condition of fish affected by these bacteria. The density of the granulomas was higher in the spleen and head kidney than either the heart or liver, and appeared to be most closely associated with the presence of an external lesion. Thirty‐eight per cent of the fish showed some sign of an external lesion. Granulomas appeared in at least one organ in 53% of the fish sampled regardless of the presence or absence of an external skin lesion. Condition factor was significantly higher for striped bass without external lesions (0.96) than those with lesions (0.82). Striped bass with no internal granulomas and no external lesion had the highest condition factor (0.99) and fish with granulomas and external lesions the lowest (0.81). Slopes of the regression log_e weight (g) and log_e length (mm) for striped bass with external lesions was significantly higher than those fish without external lesions and had a lower r². The results suggest that striped bass that are infected with mycobacteria have decreased overall health.     

饥饿胁迫对杂交鳢血液指标的影响

探索杂交鳢在饥饿不同时间状态下5项血液指标的变化情况。测定并比较饥饿处理7、14、21、28、35和42d实验组和对照组杂交鳢血液指标。结果显示,经过42d的饥饿处理,对照组与6个实验组相比,随着饥饿时间的延长,红细胞数量在0~42d内呈现下降的趋势,但在28d时测得红细胞数量突然增多,几乎达到了对照组水平,为(2.29±0.46)×1012/L。血红蛋白0~14d内呈现升高的趋势,第14d达到最高,为(82.36±7.26)g/L,在14~42d内整体上呈现降低的趋势,但在28d时测得血红蛋白含量突然升高,与14d测得的结果相当。沉降率在0~28d呈下降的趋势,28~42d内又明显上升。渗透脆性呈下降趋势。白细胞数量在0~42d内一直增加。     

养殖杂交鳢迟缓爱德华菌的分离鉴定

从患病杂交鳢[斑鳢（Channa maculata）♀×乌鳢（C.argus）♂]体内分离到2株致病菌（ZS201364-1和ZS201364-2）,通过对其生化特性与16S rRNA基因序列进行分析,确定为迟缓爱德华菌（Edwardsiella tarda）。该致病菌兼性厌氧,为革兰氏阴性短杆菌,能运动,能发酵葡萄糖、麦芽糖。吲哚试验和MR试验均为阳性。2株致病菌对杂交鳢的半致死剂量（LD50）分别为7.1×105cfu·g^-1和5.6×105cfu·g^-1。ZS201364-1最适生长温度为25～35℃、pH为7～8、氯化钠（NaCl）质量分数为1%,对头孢噻肟、环丙沙星、诺氟沙星等抗生素高度敏感。     

杂交鳢仔鱼饥饿试验及不可逆点的确定

利用人工孵化的杂交鳢初孵仔鱼,在水温(26±1)℃条件下进行其饥饿试验并确定仔鱼的初次摄食不可逆点(PNR)。结果表明,杂交鳢仔鱼孵化后第2天开始摄食,进入混合营养期,此时卵黄囊缩小至原来的1/2,与油球一同继续被仔鱼吸收;孵化后第7天卵黄囊和油球被完全吸收,混合营养期为5d。杂交鳢仔鱼最高初次摄食率出现在孵化后第6天,此时卵黄囊已吸收完全,油球有残留。当初次摄食率降至最高初次摄食率的50%时,仔鱼进入不可逆期,不可逆点出现在仔鱼孵出后的第7～8天。     

Impacts of climate change on snakehead fish value chains in the Lower Mekong Basin of Cambodia and Vietnam

ABSTRACT

The productive fisheries of the Lower Mekong Basin of Cambodia and Vietnam are essential to the food security and nutrition of 60 million people. Yet these fisheries, both culture and capture, are susceptible to the impacts of climate change. This article reports on a study undertaken to examine the vulnerability, as perceived by snakehead (Channa striata) fish farmers in Vietnam and fishers in Cambodia, to the impacts from climate change. Perceived impacts on various actors in the value chain are identified, as well as adaptation strategies currently being utilized and planned for the future. Recommendations are suggested to contribute to assisting snakehead farmers and fishers in adapting and preparing for the impacts of climate change.