Length and sex-specific associations between spiny dogfish (Squalus acanthias) and hydrographic variables in the Bay of Fundy and Scotian Shelf

The associations between spiny dogfish ( Squalus acanthias ) and hydrographic variables (temperature, salinity and depth) were examined in the Bay of Fundy and Scotian Shelf from 1970 to 1998. Data were obtained from standard groundfish bottom trawl surveys. Dogfish sex affected habitat associations. Males were found to occupy bottom water of significantly higher salinities and depths than that occupied by females. Length also significantly affected habitat associations. Smaller dogfish occupied relatively deep, high salinity bottom water compared with larger dogfish. Overall, the occupied temperatures, salinities and depths were significantly different from those which were available. Dogfish occupied warmer temperatures along a narrow range (6.62–9.19°C) compared with those which were available (1.57–9.35°C). Occupied salinity (32.70–34.43 ppt) and occupied depth (88.62–184.66 m) were also distributed along a narrower range than available salinity (32.16–34.79 ppt) and available depth (55.00–218.10 m). Sex-specific, length-specific and overall environmental preference by dogfish may bias traditional `offshore' groundfish surveys while large scale changes in hydrographic parameters may alter dogfish distribution and their interactions with other marine fauna.     

A coccolithophorid algal dermatitis of the spiny dogfish, Squalus acanthias L.

Abstract. Skin diseases of sharks and algal diseases of animals are reviewed. A specific progressive skin disease of wild, laboratory-maintained and display-aquaria populations of spiny dogfish, Squalus acanthias L., observed during a 2.5-year period at Woods Hole, Massachusetts, is described. Skin lesions, from 1mm to over 1cm in diameter, developed in the following sequence: petechial and ecchymotic haemorrhages; dome-shaped vesicles; larger lesions with central ulceration; and hyperpigmented granulations in the final repair stage. A coccolithophorid algal agent could be demonstrated in skin lesions and is described. Since both sharks and coccolithophorid algae are primitive organisms, the possible evolutionary implications of algal symbionts modified to become pathogens are discussed.     

Naturally occurring lesions and micro-organisms in two species of free-living sharks: the spiny dogfish, Squalus acanthias L., and the smooth dogfish, Mustelus canis (Mitchill), from the north-western Atlantic

Twenty-three smooth dogfish, Mustelus canis L., and 20 spiny dogfish, Squalus acanthias (Mitchill), were examined for the presence of diseases. Sharks were collected from the north-western Atlantic between April and September 2000. Major organs were sampled for histopathology and bacterial cultures were taken from kidneys. Macroscopic lesions were infrequent and included intestinal cestodiasis and gastric and dermal erosions. Microscopic lesions were common in both shark species. Mustelus canis had numerous degenerative lesions involving the pancreatic ducts, seminiferous tubules and coronary vessels. The most frequent lesions in S. acanthias were parasitic and included pancreatic nematodiasis and biliary myxosporeosis. Additionally, both species had focal meningitis, encephalitis, dermatitis, gastritis, enteritis and glomerulomesangial thickening. Microscopic parasites included intestinal coccidiosis, unclassified gastric and testicular protozoa, skeletal muscle and renal tubular myxosporeans, a branchial trichodinid ciliate, olfactory and branchial trematodes, gastrointestinal cestodes and larval nematodes. Shewanella putrefaciens , Photobacterium sp., Vibrio sp., Pseudomonas sp. and Alteromonas sp. were isolated from kidneys of nine sharks. The role of the above lesions in the natural mortality and morbidity of the two shark species is unknown. The finding that apparently healthy sharks can harbour potentially debilitating lesions warrants the inclusion of histopathological studies in the management and conservation of sharks.     

Branchial carbonic anhydrase is present in the dogfish, Squalus acanthias

The distribution of branchial carbonic anhydrase (CA) in the shark, Squalus acanthias, was studied using in situ measurements of pH disequilibrium states in post-branchial saline, and immunological techniques, immunofluorescence microscopy and Western analysis, employing rabbit polyclonal antibodies against rat pulmonary membrane associated CA IV and chick retinal cytosolic CA II. In the in situ saline perfused gill preparation, the CA inhibitor acetazolamide produced a pH disequilibium (0.063 ± 0.022 pH units) while control and bovine carbonic anhydrase perfusions did not (0.012 ± 0.017 and 0.023 ± 0.018 pH units, respectively). These results indicate that the HCO₃ ^- dehydration reaction is accelerate by endogenous extracellular CA. Western analysis of saline perfused gill membrane preparations revealed an immunoreactive 48 kDa band with the CA IV probe. In crude gill homogenates, a 33 kDa and 31 kDa pair of bands is identified by the CA II probe. The pattern of immunolabeling for CA II in the gill epithelium was either diffuse or punctate within both lamellar and filament epithelial cells while eyrthrocytes and pillar cells displayed a diffuse staining pattern.     

Reducing elasmobranch bycatch: Laboratory investigation of rare earth metal and magnetic deterrents with spiny dogfish and Pacific halibut

Spiny dogfish (Squalus acanthius) comprises a significant unwanted bycatch on demersal longlines set for halibut and cod in shelf waters of the east and west coasts of North America. In this laboratory study, attacks on baits were tested in the presence of two different rare earth materials (neodymium–iron–boride magnets and cerium mischmetal) believed to deter elasmobranch catch. Experiments were made with spiny dogfish and with Pacific halibut (Hippoglossus stenolepis) in pairwise tests of the rare earth materials and inert metal controls. Dogfish attacked and consumed baits tested with cerium mischmetal at a lower frequency than controls. Times to attack the baits were significantly higher in the presence of mischmetal, as were numbers of approaches before first attack. The time differential between mischmetal and control treatments and the number of baits consumed converged with increasing food deprivation (1 h, 2 d, and 4 d), but treatment differences were always significant. Cerium mischmetal appeared to be irritating to dogfish and may disrupt their bait detection and orientation abilities. Magnets also appeared to irritate dogfish but provided no protection for baits in feeding trials. Pacific halibut showed no reaction whatsoever to the rare earth magnets or cerium mischmetal. Mischmetal, therefore, may be useful in reducing spiny dogfish bycatch in the halibut fishery. Disadvantages in using mischmetal in commercial operations are expense, hazardous nature, and relatively rapid hydrolysis in seawater.     

Pacific herring, Clupea pallasi, recruitment in the Bering Sea and north-east Pacific Ocean, I: relationships among different populations

We examined recruitment and average weight-at-age time series for Pacific herring ( Clupea pallasi ) populations from the Bering Sea and north-east Pacific Ocean to determine similarities. Statistical correlation and multivariate clustering methods indicated Pacific herring populations form large-scale groups. Large year classes occur synchronously among several Pacific herring populations. Multivariate cluster analyses of recruitment and weight-at-age data indicated that Bering Sea herring populations are distinct from north-east Pacific Ocean populations. Within the NE Pacific Ocean, there appear to be three groups of herring populations: a British Columbia group, a south-east Alaska coastal group, and an outer Gulf of Alaska group. Jackknife and randomization tests indicate these groups are robust and not the result of random chance. Deviations from observed herring population groups were examined for indications of anthropogenic perturbations. The Prince William Sound herring populations did not show any strong deviations corresponding to the oil spill of 1989. There might not yet be enough data since the spill to detect changes in the recruitment or weight-at-age data since that time, particularly if oil spill effects were concentrated on the early life history stages.     

Age and growth of the silky shark Carcharhinus falciformis from the Pacific Ocean

ABSTRACT:   The present study estimated the age and growth of the silky shark Carcharhinus falciformis in the Pacific Ocean. Samples and biological data were collected from Japanese tuna longline and purse seine fisheries from 1992 to 1999. Vertebra centra were picked from 145 males and 153 females for age determination. The number of annual rings observed for males and females was 0–8 and 0–13, respectively. Combined sex von Bertalanffy growth equations were obtained as follows: L_t  = 216.4(1 − e^{−0.148( t +1.76)}) where L_t is precaudal length in cm at age t . A mature size for males was considered to be approximately 135–140 cm (precaudal length), with an estimated age of 5–6 years, whereas corresponding values for females were 145–150 cm and 6–7 years, respectively. Birth size ranged from 48 to 60 cm. There was no remarkable difference in growth, birth size and age at maturity between the Pacific and Atlantic Oceans. The life history parameters of the silky shark are approximately the same in both oceans.     

Body-length frequency and spatial segregation of the North Pacific spiny dogfish <Emphasis Type="Italic">Squalus suckleyi</Emphasis> in Tsugaru Strait,northern Japan

The present study elucidated the length structure and habitat segregation of North Pacific spiny dogfish (SPD) Squalus suckleyi in the Tsugaru Strait of northern Japan. Length–frequency distributions using kernel density estimation were determined for SPD captured by the bottom longline fishery landed at Minmaya from 1999 to 2011 and at Ohma from 2007 to 2011. Length–frequency distributions significantly differed between landings at the two ports; SPD at Minmaya were on average larger (65–85 cm precaudal length: PCL) than at Ohma (55–75 cm PCL). This difference is evidence of the length-based spatial segregation of the SPD. The seasonal landing pattern of the SPD was also different between the two ports. The SPD landed at Minmaya were largest during February–June and SPD < 75 cm PCL were caught at Ohma throughout the year. This different landing pattern was related to seasonal differences in bottom-layer water temperatures between the two fishing grounds. Females were thought to be dominant at Minmaya, whereas males dominated in most of the catches at Ohma. These results suggest spatial patterns of sexual segregation for this species in the Tsugaru Strait and require elucidation of the SPD stock condition at Minmaya and Ohma.     

Genetic population structure in the Chilean jack mackerel, Trachurus murphyi (Nichols) across the South-eastern Pacific Ocean

The Chilean jack mackerel Trachurus murphyi, is a pelagic fish from the Carangidae family that is distributed in the South Pacific Ocean. Because this species constitutes an important economic resource across the South Pacific and plays an important ecological role in this ecosystem there is a growing interest in determining its population structure. In this study, we used molecular markers (mitochondrial DNA sequences and microsatellites) from Chilean jack mackerel samples to investigate its genetic population structure across the South Pacific Ocean. The mitochondrial DNA did not detect a genetic structure in T. murphyi populations in the Pacific Ocean, but revealed very low haplotype diversity and a short genealogy history compared to other small-pelagic species. The same general pattern of a lack of genetic structure was found with microsatellite loci; however, a large genetic diversity was revealed with microsatellite markers. The present results did not support the existence of different stock units for T. murphyi across the South Pacific Ocean but a more holistic approach will be necessary to determine an adequate management strategy for this fishery.     

福建漳浦太平洋牡蛎微卫星等位基因比较

本文采用Ucdcg153、157、202微卫星分子标记对福建漳浦从广东饶平引人的太平洋牡蛎育苗亲贝进行等位基因比较.两组样品(Cg♀和cg♂)携带的等位基因在微卫星重复区间及其附近存在高度相似的变异特征.这些特征区间分别是:Ucdcg153 23～40位碱基区间,Ucdcg157 73～100位碱基区间,Ucd-cg2...     

An epizootic of lymphoma in northern pike, Esox lucius L., from the Åland Islands of Finland

Abstract. An epizootic of lymphoma in northern pike, Esox lucius L., occurring in the Åland Islands in Finnish waters of the Baltic Sea is described. Macroscopic inspection of 19 tumorous pike, 17 males and two females, as well as tissue observations by light and electron microscopy showed that this lymphoma is similar to those previously reported in esocid fishes from North America, Ireland and Sweden. Haematoxylin and eosin-stained light microscopic sections of tumour tissue suggested its classification as a lymphoblastic or stem cell lymphoma. Tumour cells cultured during several months at 4°C showed morphological features of differentiation and resembled plasma cells. No conclusive evidence of the presence of viruses in the lesion was obtained.     

Occurrence of postmortem myoliquefactive kudoosis in Atlantic mackerel, Scomber scombrus L., from the North Sea

Members of the myxosporean genus Kudoa occur in various marine teleosts worldwide. Several species are of concern to the fishery and aquaculture industries as they may produce unsightly cysts in the fish host's musculature or are associated with postmortem myoliquefaction of the fish muscle, commonly referred to as 'soft flesh'. This study describes the occurrence and effects on a host of a Kudoa species in Atlantic mackerel, Scomber scombrus , from the northern North Sea. Generalized postmortem myoliquefaction associated with Kudoa sp. occurred in 0.8% of the examined fish, i.e. 11 of 1339 mackerel developed 'soft flesh'. There was a significant difference in the prevalence of myoliquefaction between medium sized (400–600 g) and large mackerel (>600 g). The prevalence reached 8.9% in the latter host size group. No subclinical infections of Kudoa sp. were detected when examining fresh muscle ( n  = 103) and blood ( n  = 165) samples for spores using light microscopy. Affected mackerel developed generalized myoliquefaction after 38–56 h post-catch. No inflammatory host response was associated with the presence of plasmodia within single body muscle fibres of 'soft flesh' affected fish. Based on comparison of myxospore dimensions and analysis of the nuclear small subunit (SSU) ribosomal DNA, the present Kudoa species is assigned to Kudoa thyrsites . However, due to the species' apparently very wide geographical distribution and host range, its varying effect on different fish host species, together with the still unknown life cycle of Kudoa spp., the taxonomic status of K. thyrsites appears not to be fully resolved.     

Homing patterns of Baltic salmon, Salmo salar L., from smolts released from two hatcheries in the River Dalälven, Sweden

The River Dalälven Baltic salmon, Salmo salar L., population has been maintained by stocking reared fish since the early 1920s. Initially, all rearing was carried out at one hatchery, but since the late 1980s two have been used. Both hatcheries are situated 9–10 km from the river mouth but some 600 m apart. All broodfish were caught in a single fish trap situated some 700 m upstream of the upper hatchery. The salmon smolts were released just below the water outlets of each hatchery, respectively. About 2% of the released smolts from each hatchery were tagged annually with Carlin tags. Total recapture rates were higher for smolts from the lower hatchery. A higher proportion of recaptured fish was reported from the home river for salmon from the upper hatchery. The migration within the river to the fish trap was more precise for fish from the upper station. Strays were very late in the season and of a higher number from the lower hatchery. Observations of jumping salmon by the outlet from the lower station indicated that salmon returned to that point. The lower recaptures in the trap were considered a result of a shorter river migration of salmon from the lower hatchery.     

Acute stress alters the intestinal lining of Atlantic salmon, Salmo salar L.: An electron microscopical study

Groups of Atlantic salmon (Salmo salar L.) in feeding (guts filled with faeces) or fasted (three days of diet deprivation) states were subjected to 15 minutes of acute stress. Blood samples and intestinal tissue were collected and prepared for chemical and ultrastructural analyses at intervals post stress until 53 h of recovery. Subjecting fish to acute stress led to significant alterations of the ultrastructure of the enterocytes lining the gastrointestinal tract (GI tract). The most notable effect was substantial damage to the intercellular junctional complexes in midgut regions. These effects appeared within the first hour after stress, were maintained for at least 12 h and were more pronounced in fed than fasted fish. In contrast, hindgut was influenced less by stress and damage was rarely observed. Stress also influenced fish intestinal microbiota. Adherent bacteria decreased in both midgut and hindgut of stressed fish, and this was accompanied by a significant increase in the bacterial contents of faeces. It is suggested that this was due to the sloughing off of mucus eliminating existing microflora and allowing remaining bacteria (also pathogenic) in the gut lumen to colonize the surface of the enterocytes. Although blood haematocrit and plasma cortisol increased following stress, the response appeared to be greater in fasted fish. There were also significant differences in carbohydrate metabolism. While liver glycogen stores were depleted in fasted fish following the mobilization of glucose into plasma, liver glycogen was never depleted in fed fish. As a consequence, plasma glucose levels remained high for more than 12 h of recovery. In fed fish, plasma lactate was also higher than in fasted salmon, and the clearance rate appeared slower. Acute stress induced oxidative stress, as measured through plasma malondialdehyde, but the effect was marginal and nonsignificant. This revised version was published online in July 2006 with corrections to the Cover Date.     

An examination of the intestinal tract of Atlantic salmon, Salmo salar L., parr fed different varieties of soy and maize

This study was conducted to investigate the long-term effects of feeding plant products from both traditional breeding and from biotechnology on intestinal somatic indices, histology and cell proliferation in first-feeding Atlantic salmon, Salmo salar L. (initial weight 0.21 +/- 0.02 g). A standard fishmeal diet (standard fishmeal) was formulated to contain fishmeal as the sole protein source and suprex maize as the main starch source. Six experimental diets were then developed: two in which some of the fishmeal was replaced with commercially available, genetically modified Roundup Ready full-fat soybean meal (GM-soy) or commercially available, non-GM full-fat soybean meal (nGM-soy) at a level of 12.5% of the total diet, and four diets in which the suprex maize was replaced with two lines of GM-maize (Dekalb 1; D1 and Pioneer 1; P1), both products of event MON810, and their half-sibling non-GM counterparts (Dekalb 2; D2 and Pioneer 2; P2), at a level of 12.1% of total diet. Each diet was fed to fish in triplicate tanks and the experiment lasted for 8 months, during which the fish reached a final weight of 101-116 g. There was no significant effect of diet on the intestinal indices, nor were histological changes observed in the pyloric caeca or mid intestine. In the distal intestine, one of nine sampled fish fed nGM-soy showed moderate changes, two of nine sampled fish fed GM-soy showed changes, one with moderate and one with severe changes, and two of nine fish fed nGM-maize D2 had moderate changes. Using a monoclonal antibody against proliferating cell nuclear antigen (PCNA), cell proliferative responses to the experimental diets were assessed. In fish fed both soy diets, a significantly higher (P < 0.05) cell proliferation response was observed in the distal intestine concomitant with an increased localization of PCNA positive cells along the whole distal intestinal folds. The PCNA response among the nGM-soy group was significantly higher compared with all the other diet groups. In contrast, for fish exposed to dietary maize (type D) compared with fish fed the standard fishmeal, the soy-diets (GM-soy and nGM-soy) and maize (type P), a significantly lower (P < 0.05) cell proliferation response was observed in the distal intestine. Results indicated that the GM plant products investigated in this study, at about 12% inclusion level, were as safe as commercially available non-GM products, at least in terms of their effect on indices and histological parameters of the Atlantic salmon intestinal tract.     

Influence of river flow on rod catch of Atlantic salmon, Salmo salar L., from the lower River Derwent, north-west England

Abstract Twenty-seven years of daily salmon, Salmo salar L., rod catch and flow data from the River Derwent were analysed. Daily catch was standardized for each month between June and October and the mean value determined for each 2-cumec flow band. In June and July the mean standardized catch remained relatively low and stable for flows up to approximately 9 cumecs. Thereafter it increased steadily with increasing flow, reaching a peak at 21 cumecs and 41 cumecs for each month respectively. A linear model accounted for the greatest proportion of the variability in August and September with mean standardized catch increasing steadily up to a maximum value of 43 and 39 cumecs respectively. However, in October, a quadratic model was more appropriate, with mean standardized catch decreasing as flow increased up to 9 cumecs and thereafter increasing steadily with flow, reaching a maximum value at 21 cumecs. The pattern of the relationship at higher flows was not clear because of the paucity of data. These findings are discussed in relation to the management of the water resource for the maintenance of the fishery.