Atypical Aeromonas salmonicida infection in naturally and experimentally infected cod, Gadus morhua L.

Cod, Gadus morhua L., of wild origin, were reared at different temperatures for 12 months. During this period, moribund and newly dead fish were examined and samples collected for bacteriology and histopathology. Atypical Aeromonas salmonicida was isolated from 10 individuals reared at or above 7 °C. The isolates were homogeneous with respect to biochemical and antibiogram characters and similar to the ssp. achromogenes National Collection of Industrial and Marine Bacteria, UK, type strain 1110 and reference strains that have been isolated from salmonids and haddock in Iceland. Histopathological analysis of the naturally infected cod showed typical ulceration associated with atypical A. salmonicida infection and also widespread granulomatous formations. One‐year‐old cod of farmed origin, kept at 9 °C, received intraperitoneal or intramuscular injection with different doses of atypical A. salmonicida, isolated from the above wild cod. Mortalities were monitored for 28 days and the LD₅₀ calculated. The route of bacterial injection influenced the mortality rate and LD₅₀ value and affected, to some extent, the pathological changes observed and humoral immune parameters. Pathological changes, including haemorrhage, early stages of granuloma formation and necrotic changes, were seen in several organs. Infection appeared to induce non‐specific antibody activity against trinitrophenyl (TNP)‐haptenated protein and may have activated the complement system. Specific antibody response against atypical A. salmonicida was not detected.     

几种深水网箱养殖鱼类行为习性的观察

运用鱼类生态学、鱼类行为学以及水产养殖学研究方法，对几种深水网箱养殖鱼类的行为习性进行了观察，结果表明：对干露的耐受力强弱依次为黑鲷、真鲷、鲈鱼、美国红鱼和大黄鱼；大黄鱼分布于中下层网箱边缘、集群、不争斗，美国红鱼均匀分布于中下层、集群、争斗激烈，鲈鱼均匀分布于中下层、较少集群、争斗激烈，真鲷分布于下、底层网箱边缘、较少集群、争斗，黑鲷分布于下、底层网箱边缘、较少集群、争斗；摄食节律明显，与潮水涨落有关，在接近早晨、傍晚的平潮或停潮时间内形成两个摄食高峰；对饵料具有选择性，对饥饿的耐受能力较强，不同投饵方式对鱼类摄食强度有影响，对饥饿的耐受力随着水温的降低而增强；7-8月份日平均摄食率最高，2月份最低，鱼类的摄食率与水温有密切的关系；昼夜活动习性不明显，流急时分布于网箱底部或下游网箱边缘，流缓时活动分布范围明显扩大；抗风、浪、流能力强弱依次为美国红鱼、鲈鱼、大黄鱼、黑鲷、真鲷。     

Quality Changes During Salt-Curing of Cod (Gadus morhua) at Different Temperatures

ABSTRACT

The main aim of this study was to assess the quality changes and their causes during cod salt-curing for up to 76 days at different temperatures and a relative humidity below 80%. Salt-curing made the fish more yellow (L*a*b* scale), a color change that is more easily detected in sensory analysis against a cream color scale. Intense proteolytic breakdown took place at 12 and 18°C, leading to a greater proteolysis degree and a higher pH. A red surface discoloration of the flesh was apparent after 76 days at 18°C due to the high number of red-halophilic bacteria. These bacteria were also responsible for the highest intensity of “off”-odors and mucus obtained under these conditions. Cod salt-curing should be done below 12°C to reduce the spoilage activity of halophilic bacteria and is best done at chill temperature (close to 6°C) to obtain a good quality product.     

Benchmarking growth of farmed Atlantic cod,Gadus morhua: a case study in Ireland

The growth performance of different stocks of farmed North Atlantic cod over several years in Irish rearing conditions is described. The growth trajectories for all stocks reared were similar. From all growth data, it was found that weight at 180 and 365 days post hatch (dph), with mean values of 17.7 and 158.7 g, respectively, are accessible and useful indicators of hatchery growth performance. The importance of using standard benchmarking points to facilitate concerted and improved research efforts is highlighted here. Growth performance was evaluated against existing predictive models and these were found to be quite robust and very useful within certain constraints. Comparative growth modelling using prevailing ambient sea surface temperature regimes for five different countries (Ireland, Norway, Canada, Iceland and the Faeroes) was also undertaken. Harvest size of 2.5 kg was estimated to be reached in approximately 36 months post hatch in the Faeroes, 38 months in Ireland, 37 months in Norway, 40 months for Canada and up to 42 months in Iceland.     

Exploring the temperature optima and growth rates of Atlantic cod at the south‐easterly limit of its range

Four size groups of juvenile farmed Celtic Sea cod (2.7–41.8 g) were reared at a range of constant temperatures (8–19°C). The optimum temperature for growth (T_opt.G) decreased from 15.1°C for ~3 g fish to 12.5°C for ~42 g fish. A comparison of these results with those published for a more northerly population (Icelandic) suggests that there is no significant difference in the optimal temperature for growth of cod stocks within the size range studied. In contrast, the growth rates of Celtic Sea cod were lower than those derived from these established models (for a northerly stock) for small juveniles (<5 g), but similar for larger fish (>40 g). Thus, while T_opt.G appears fixed across the range, there may be high plasticity in local growth performance throughout the Holarctic distribution. Some possible explanations for these differences are considered.     

总氨态氮对太平洋鳕仔稚鱼的急性毒性研究

为确保太平洋鳕Gadus macrocephalus人工育苗生产过程中的水质安全,采用换水式水生生物毒性试验方法,研究了总氨态氮对不同规格(体长4.37、4.88、5.83、7.46 mm)太平洋鳕仔稚鱼的急性毒性。结果表明:在水温为8.5~10.0℃、pH为7.96~8.14、溶氧为7.0~8.0 mg/L、盐度为29~30条件下,水中总氨态氮对不同日龄太平洋鳕仔稚鱼的毒性不同;对于4、15、22和35日龄的太平洋鳕仔稚鱼,水中总总氨态氮的安全浓度分别为11.518、9.576、1.982、0.959 mg/L,对应非离子氨态氮的安全浓度分别为0.219、0.182、0.038、0.018 mg/L。研究表明,随着太平洋鳕仔稚鱼个体的发育,其对水中总氨态氮的耐受能力逐渐降低。     

Ecological role of the giant root‐rat (Tachyoryctes macrocephalus) in the Afroalpine ecosystem

Rodents with prevailing subterranean activity usually play an important role in the ecosystems of which they are a part due to the combined effect of herbivory and soil perturbation. This is the case for the giant root‐rat Tachyoryctes macrocephalus endemic to the Afroalpine ecosystem of the Bale Mountains, Ethiopia. We studied the impact of root‐rats on various ecosystem features within a 3.5‐ha study locality dominated by Alchemilla pasture, which represents an optimal habitat for this species, in 2 periods of a year. The root‐rats altered plant species composition, reducing the dominant forb, Alchemilla abyssinica, while enhancing Salvia merjame and a few other species, and reduced vegetation cover, but not the fresh plant biomass. Where burrows were abandoned by root‐rats, other rodents took them over and A. abyssinica increased again. Root‐rat burrowing created small‐scale heterogeneity in soil compactness due to the backfilling of some unused burrow segments. Less compacted soil tended to be rich in nutrients, including carbon, nitrogen and phosphorus, which likely affected the plant growth on sites where the vegetation has been reduced as a result of root‐rat foraging and burrowing.     

Molecular identification of laser‐dissected gut contents from hatchery‐reared larval cod,Gadus morhua: a new approach to diet analysis

The transition between endogenous and exogenous feeding in hatchery production of fish larvae has long been a bottleneck to increased production. Identification of alternative prey species with a wider array of nutritional profiles is essential for further expansion and diversification within the aquaculture industry. Traditional morphological methods to identify dietary composition are limited. In this study, we present a novel DNA‐based methodology for identifying the gut contents of larval fish that is independent of prey retaining identifiable characteristics. Laser capture microdissection is used to collect ingested material for DNA extraction, thus limiting contaminating DNA originating from the larval fish. PCR is then conducted using universal eukaryotic primers that have the potential to detect a wide diversity of prey items. Using this approach, we identified ingested Artemia salina from hatchery‐reared Gadus morhua larvae. Differential length amplification PCR was used to evaluate the effects of DNA degradation on the sensitivity of A. salina detection. Although it was possible to detect A. salina with relatively long (626 bp) fragments, targeting smaller fragments (264 bp) resulted in the highest return of prey sequences. This combined LCM and molecular approach to diet analysis could offer a more complete assessment of the diets of naturally feeding larvae.     

A follow‐up study of selected biomarkers of health in cod Gadus morhua L. collected from the southern Baltic off the Polish coast

Selected biomarkers of health were examined in 50 post‐spawning cod Gadus morhua collected in November 2015 from the southern Baltic. The biomarkers included condition factor (CF), macroscopic lesions, histopathology of spleen, liver and gonads, and morphometry of follicular atresia and hepatic and splenic melanomacrophage cells (MMC). All fish appeared in good body condition. One fish had a dermal ulcer, and in seven, macroscopic nematodes were noted within body cavity. Microscopic lesions in the liver included biliary myxozoanosis, microsporidial and necrocentric granulomas, parasitic hepatitis, multifocal necrosis, foci of cellular alterations, spongiosis, peliosis and cytoplasmic fibrillar inclusions. The spleen and gonads had microsporidial and/or necrocentric granulomas. Some of the biomarkers showed differences as compared to spawning cod collected in May from the same location in 2012, most importantly values an order of magnitude lower for splenic MMC in post‐spawning fish. In post‐spawning fish, there were statistically significant correlations between MMC, CF, follicular atresia, parasitic hepatitis and microsporidiosis. This is the first comparison of biomarkers of health in post‐spawning and spawning Baltic cod. Future studies need to examine the relationships of biomarkers to levels of pollutants in the environment and in tissues of cod.