Changes in the parasite fauna of whiting Odontogadus merlangus L. with age and sex of host, season, and from different areas in the vicinity of the Isle of Man

Infestation of whiting with the helminths Derogenes varicus Müller, Hemiurus communis Odhner, Grillotia erinaceus Van Beneden (plerocercoids) and Contracaecum clavatum Rudolphi, and the copepod Lernaeocera branchialis L., increased with the age of the fish but infestation with the helminths Lecithaster gibbosus Rudolphi, Stephanostomum pristis Looss and Podocotyleatomon and the copepod Clavella uncinata Müller decreased as the fish aged. Infestation with the gill monogenean Diclidophora merlangi Kuhn remained at much the same level in fish 1–5+ years old. Derogenes, Hemiurus, Lecithaster, Cotracaecum and Stephanostomum showed seasonal fluctuations in the levels of their populations in whiting. In all cases the parasites reached a main peak in the summer and early autumn, a time when juvenile digeneans were most apparent.
Whiting from Morecambe Bay were less infested with Clavella than whiting taken from other areas. Experimental evidence suggests that the lower salinity of Morecambe Bay may be responsible; however, this could not account for the lower infestation of Morecambe Bay whiting by Diclidophora which appeared to be unaffected by a lowered salinity. Whiting from the east side of the Isle of Man were more infested with Lernaeocera but less infested with Diclidophora than fish from the west side of the island. The myxosporidian Myxobolus aeglefini Auerbach was externally visible in the sclera of whiting from the east side of the island but absent from the sclera of whiting from the west side of the island. It is, therefore, suggested that whiting to the east of the Isle of Man form a separate sub-stock from those to the west of the island.     

The fish populations in inshore waters of the west coast of Scotland. The food and feeding of the whiting (Merlangius merlangus L,.)

The food and feeding of the whiting ( Merlangius merlangus ) of the inshore waters and sea lochs of the west of Scotland were studied from 1969–1973. Fish and Crustacea were the main food items and their occurrence in the stomachs was clearly related to the size of the whiting and also to their seasonal abundance. The diurnal changes in feeding were also investigated and the results indicated that the size of fish was again an important factor which could affect the interpretation of the seasonal data.     

Movements of 0-group plaice Pleuronectes platessa L. as shown by latex tagging

0-group plaice were caught in Red Wharf Bay, Anglesey, North Wales, tagged with coloured liquid latex, and released in the bay or, after transplantation, at a position on a sandbank 3–5 km offshore. The pattern of movement shown by recaptures of plaice caught and released at the same position in the bay was one of extremely restricted movement of less than 0–5 km over several months, with only a slight interchange of fish between the sides of the bay and the centre. These restricted movements contrasted sharply with relatively long distances travelled by fish displaced to an unusual depth and position offshore and to a position at the other side of the bay 3 km away. In the first case a high proportion returned rapidly to the usual depth preference inshore and in the second a recapture pattern significantly different from that of control fish was demonstrated. Both results indicated a return to a preferred or familiar situation.     

Mitochondrial DNA sequence variation and genetic stock structure of Atlantic cod (Gadus morhua) from bay and offshore locations on the Newfoundland continental shelf

Bay cod, Atlantic cod (Gadus morhua) that over-winter in the deep-water bays of northeastern Newfoundland, have historically been regarded as distinct in migration and spawning behaviour from offshore (Grand Bank) cod stocks. To investigate their genetic relationships, we determined the DNA sequence of a 307-base-pair portion of the mitochondrial cytochrome b gene for 236 adult cod taken from the waters off northeastern Newfoundland, including fish found over-wintering and spawning in Trinity Bay. Although 17 genotypes were found, a single common genotype occurs at a frequency of greater than 80% in all samples, and no alternative genotype occurs at a frequency of greater than 3%. Genotype proportions did not differ significantly among samples. Measures of genetic subdivision among sampling locations are nil. Cod over-wintering in Trinity Bay are not genetically distinct from offshore cod. In combination with tagging and physiological studies, these data suggest that there is sufficient movement of cod between bay and offshore locations to prevent the development or maintenance of independent inshore stocks. Adult cod that over-winter in Trinity Bay appear to represent an assemblage of temporarily nonmigratory fish that have become physiologically acclimated to cold-water inshore environments. The pattern of genetic variation in northern cod suggests a recent population structure characterized by extensive movement of contemporary individuals superimposed on an older structure characterized by a bottleneck in the population size of cod in the north-western Atlantic.     

Bay-scale population structure in coastal Atlantic cod in Labrador and Newfoundland, Canada

Polymorphisms at five microsatellite DNA loci provide evidence that Atlantic cod Gadus morhua inhabiting Gilbert Bay, Labrador are genetically distinguishable from offshore cod on the north-east Newfoundland shelf and from inshore cod in Trinity Bay, Newfoundland. Antifreeze activity in the blood suggests that Gilbert Bay cod overwinter within the Bay. Gilbert Bay cod are also smaller (weight and length) for their age and consequently less fecund for their age, than cod elsewhere within the northern cod complex. The productivity and recruitment potential of coastal cod off Labrador may thus be much lower than that of offshore northern cod or of inshore cod farther south, implying that a more conservative management strategy may be required for cod from coastal Labrador than traditionally practised for northern cod inhabiting less harsh environments. Relatively high F _ST and R _ST measures of population structure suggest that important barriers to gene flow exist among five components that include two inshore (Gilbert and Trinity Bay) and three offshore cod aggregations on the north-east Newfoundland Shelf and the Grand Bank. D _A and D _SW estimates of genetic distance that involve Gilbert Bay cod are approximately three- and 10–fold larger, respectively, than estimates not involving Gilbert Bay cod. The differences between inshore cod from Gilbert Bay and Trinity Bay raise the possibility that other genetically distinguishable coastal populations may exist, or may have existed prior to the northern cod fishery collapse. Harvesting strategies for northern cod should recognize the existence of genetic diversity between inshore and offshore components as well as among coastal components.     

Seasonal and interannual variation in abundance of Calanus finmarchicus (Gunnerus) and Calanus helgolandicus (Claus) in inshore waters (west coast of the Isle of Man) in the central Irish Sea

The seasonal and interannual variability in abundance of Calanusfinmarchicus and Calanus helgolandicus in the Irish Sea wasexamined on the west side of the Isle of Man (central IrishSea) between 1995 and 2001. There was considerable interannualvariability in abundance of both species that was greater thanthat seen in adjacent seas. In general, maximum abundance occurredbetween May and July each year with C. finmarchicus tendingto occur earlier in the year than C. helgolandicus. There wasa significant difference in interannual maximum abundances inthe area (14–18 stations treated as replicates) with mostyears having a low abundance and one year a relatively highabundance. The maximum abundance of C. finmarchicus (1996) coincidedwith a low (negative) index value of the North Atlantic Oscillation(NAO), and with a high abundance of young gadoids (cod, haddockand whiting) in the water column and a large settlement of plaice.A high abundance of C. helgolandicus coincided with a relativelyhigh (positive) index value of the NAO in 2000. The magnitudeof interannual and seasonal variability in abundance was inclose agreement with data from an inshore area (Port Erin Bay,Isle of Man) between 1907 and 1920. As with many Calanus populations,the adults in both species were predominantly female. As shownpreviously, Calanus is not one of the numerically dominant copepodspecies in the Irish Sea. However, the presence of young stagesof Calanus within the central Irish Sea suggests that it mustsupport a breeding population.     

Winter growth of juvenile plaice on the Port Erin Bay (Isle of Man) nursery ground

Juvenile plaice ( Pleuronectes platessa ) were studied in Port Erin Bay, Isle of Man, U.K. between September and March 1989/1990 and 1990/1991. Plaice (>90 mm) were tagged and individual growth rates calculated for the autumn, winter and over-winter time periods. During the study the population of fish >90 mm remained fairly stable both within a study season and between years. Autumn growth rates ranged from 0 to 0.39 mm day⁻¹ (mean₁₉₈₉=0.13 mm day⁻¹, mean₁₉₉₀=0.10 mm day ⁻¹) and winter 0 to 0.5 mm day⁻¹ (mean₁₉₉₀=0.11 mm day⁻¹ and mean₁₉₉₁=0.17 mm day ⁻¹). In general, growth rates were higher at higher mean seasonal temperatures. However, relative growth rate was significantly higher in the colder winter period of 1991 than 1990.     

The life-history strategy of deepwater sculpin, Myoxocephalus thompsoni (Girard), in Lake Michigan: dispersal and settlement patterns during the first year of life

Deepwater sculpin, Myoxocephalus thompsoni (Girard), were sampled from six stations from the 15–100 m depth contours in Lake Michigan between April 1983 and July 1984. In south-eastern Lake Michigan M. thompsoni lay benthic eggs in offshore waters, which hatch between November and August, with peak hatching in March. Abundance of larvae in pelagic samples was higher offshore than inshore, but larval size was greater and development more advanced at inshore stations, indicating an inshore movement after hatching. Larvae reached metamorphosis at 20 mm and settled to the bottom beginning in July. Pelagic larvae 20–40 mm were found in the lower water column at all stations, but newly settled individuals were only captured with bottom trawls at inshore locations (≤60 m depth). Data from ichthyoplankton and bottom trawl samples in 1983 and 1984 indicated that locations for successful settlement of larvae to the bottom extended only as deep as the shallowest fringe of the adult population (> 50 m in 1983). In 1983, maximum density of larvae reached 0.4 individuals m⁻³ by June. Survival from the pelagic larval stage to the demersal young-of-year stage in 1983/1984 was c . 0.1–0.4%. The specific mechanism of mortality at the time of transition to a demersal habit has not been determined.     

The novel use of pop‐off satellite tags (PSATs) to investigate the migratory behaviour of European sea bass Dicentrarchus labrax

A total of 12 adult European sea bass Dicentrarchus labrax were tagged with pop‐off satellite archival tags (PSAT) in Irish coastal waters and in offshore waters in the north‐east Celtic Sea between 2015 and 2016. Archived data were successfully recovered from five of the 12 tags deployed, three from fish released in inshore Irish waters and two from fish released offshore in the eastern Celtic Sea. All three fish tagged in inshore waters were found to undertake migrations into the open ocean coinciding with the spawning period. These fish also exhibited fidelity to inshore sites post‐migration, returning to the same general location (within c. 73 km, which is roughly the predicted mean accuracy of the method) of their original release site. Although the number of tracks obtained here was limited, some degree of aggregation between inshore and offshore tagged fish in the eastern Celtic Sea was noted during the expected spawning period suggesting PSATs can provide new information on specific spawning locations of European sea bass.     

Evidence for secondary planktonic transport of post‐larvae of seagrass‐associated King George whiting

Stomach contents and stable isotope analyses were used to determine if secondary planktonic dispersal of King George whiting Sillaginodes punctata post‐larvae from shallow inshore habitats in a large embayment in south‐eastern Australia was initiated by wave disturbance. Benthic harpacticoid copepods, which live in and amongst seagrass shoots, were found in the stomachs of S. punctata caught offshore in the plankton only during rough weather. Stable isotope analyses showed that the base of nutritional support, estimated from values of δ¹³C, of S. punctata collected in the plankton changed significantly during rough (waves > 0·25 m) compared to calm (waves < 0·25 m) weather conditions. Values of δ¹³C collected from S. punctata in the plankton during rough weather were more consistent with S. punctata values found in the seagrass. Sillaginodes punctata collected in the plankton and seagrass during rough and calm weather failed to show differences in δ¹⁵N values. Dietary and isotope analyses support a model whereby newly arrived S. punctata larvae can be resuspended from seagrass beds and dispersed offshore by wave action during onshore winds. Secondary planktonic dispersal in S. punctata would provide a mechanism by which seagrass beds further inside Port Phillip Bay are colonized.     

Biological tags for stock separation in Pacific herring Clupea harengus pallasi in California.

A survey of the parasites of Pacific herring (Clupea harengus pallasi) off northern California identified 1 species of Acanthocephala, 1 species of Cestoda, 2 species of Copepoda, 1 species and 1 family of Digenea, 3 species of Nematoda, and 3 species of Protozoa. From this survey, Lacistorhynchus dollfusi (Cestoda), Parahemiurus merus (Digenea), and Anisakis simplex, Contracaecum sp., Hysterothylacium sp. (Nematoda) were selected as potential tags. Herring were collected in Tomales, San Francisco, and Monterey bays for the following 9 yr and examined for these select parasites. The results suggest that these parasites can be used to distinguish the spawning stocks of San Francisco and Tomales bays. The distribution of the definitive hosts of the respective parasites suggests that the Tomales Bay fish are offshore during the nonbreeding season and the San Francisco Bay fish onshore. The similarity in parasitism between San Francisco Bay and the nonspawning population in Monterey Bay suggests that these 2 populations represent a single stock.     

The food of larval blue whiting, Micromesistius poutassou (Risso), in the Rockall area

Larval blue whiting of 3–42 mm total length, taken in 1967 and 1968 in the Rockall Bank area, were found to have fed almost exclusively on various stages of small crustaceans; the eggs, nauplii and copepodites of copepods, along with fewer numbers of larval euphausiids and Evadne nordmanni , formed the major proportion of the diet. The guts of the larger larvae contained a greater number of, and larger organisms, than those of the smaller larvae. Feeding incidence was generally lower at night. There was a general increase in the weight of the gut contents as the daylight hours progressed followed by a decrease during the night. Diurnal variation in the percentage composition of the food was also demonstrated. Comparisons of the diet in the two years showed that more food was consumed by almost all sizes of larvae in 1968.
It has previously been suggested that blue whiting larvae may find better feeding conditions on Rockall Bank than off the Bank. However the present study suggests that larvae, particularly of 8 mm and longer, took more food when off the Bank. A brief comparison is made of the gut contents of the larvae of blue whiting and of the other eight most abundant species.     

Analysis of the demersal community of fish and cephalopods on the Agulhas Bank, South Africa

The demersal fish and cephalopod communities of the continental shelf and upper slope from 17 to 395m deep were studied during five annual cruises between Cape Agulhas and Port Alfred, South Africa. The cruises showed a consistent pattern of an inshore community (<100m), a shelf community ( c . 90–190m) and a shelf-edge/upper slope fauna (>200m). These groups were identified by dendrograms and multidimensional scaling cluster analysis, which supported on-board observations of catch variation with depth. Although the boundaries are not clearly defined, examination of physical features at the clustered stations suggests that depth, temperature and, to a lesser extent, oxygen concentration are important in the grouping. Occasional, apparently anomalous associations of inshore stations suggested that water temperature and oxygen may over-ride the normal depth distributions of the species groups. This intimates that patterns offish and cephalopod distribution may be dynamic and in part related to the physical parameters of the water body.     

The distribution of some helminth and copepod parasites in tissues of whiting, Merlangius merlangus L., from Manx waters

In an examination of 1352 whiting 0–5+ years old from Manx waters it was found that the digeneans Hemiurus communis Odhner and Derogenes varicus Müller were restricted to the stomach. Stephenostomum pristis Looss, Podocotyle atomon Rudolphi and Leci-thaster gibbosus Rudolphi were most commonly found in the anterior intestine and caeca of mature fish but were found more posteriorly along the intestine of young whiting. The metacercaria of Cryptocoty lingua Creplin were found predominantly in the skin above the lateral line. The fins contained fewer cysts than expected from the area available. Plerocercoids of Grillotia erinaceus Van Beneden mainly infested the musculature of the pyloric stomach and those in the perivisceral cavity were concentrated in the extreme posterior corner. Unencapsulated forms of the nematode Contracaecum clavatum Rudolphi were commonest in the anterior intestine and stomach. Encapsulated forms were most abundant in the liver. The acanthocephalan Echinorhynchus gadi Rudolphi was usually found in the posterior intestine and its presence further restricted Contracaecum to the anterior intestine. In young whiting over two-thirds of the copepod Clavella uncinata Müller were attached to the operculum and posterior rim but in older whiting the majority were attached to the gill rakers. The first gill arch was the most heavily infested and the middle region of the gill arches contained most parasites. The frequency distributions of most of the helminths described more or less a negative binomial distribution. The frequency distribution of Contracaecum did not conform to either a negative binomial or a Poisson distribution.     

Accumulation of plerocercoids of Triaenophorus crassus in the second intermediate host Coregonus lavaretus and their effect on growth of the host

Patterns of accumulation of Triaenophorus crassus in its second intermediate host whitefish Coregonus lavaretus s.l. were studied between 1991 and 1996 from two host populations in two separate areas of Lake Saimaa, Finland. Whitefish were infected commonly with several T. crassus plerocercoids and the parasites were aggregated into the oldest hosts. In one host population the annual parasite accumulation was 0·9 parasites in all host age groups between 3 and 8 years. In the other host population the annual accumulation was 1·6 parasites in 3–5-year-old fish, but increased up to 3 to 4 parasites per year in fish over 5 years old. The increase did not coincide with the period of maturation or any increase in whitefish growth, both of which could alter the food intake of the fish. The sharp increase in the annual accumulation suggests a threshold intensity above which the probability of acquiring further parasites increases. In spite of a heavy aggregation of parasites there was no evidence of parasite-induced host mortality. The annual increase in mean abundance was not correlated with the mean annual weight increase in 2–4-year-old fish within cohorts. However, evidence of a negative effect of parasites on whitefish growth was revealed by back-calculation of lengths of uninfected and infected whitefish and correlations between length or weight of fish and intensity of infection with fish age. Both analyses suggested that larger young fish harboured more parasites than the smaller ones while in older fish the reverse was true, a pattern that has not been shown earlier for parasitized fish.     

Population biology of the myctophid fish Gymnoscopelus nicholsi (Gillbert, 1911) from the western South Atlantic

Thirty-three collections of Gymnoscopelus nicholsi were made between 1976 and 1981 in the South Atlantic using both krill and bottom trawls. In the Antarctic waters the main part of the stock consisted of adult fish 3–7 years old, characterized by a benthopelagic mode of life. Fish of year-class I were observed only in the vicinity of South Georgia, South Sandwich Islands and the Scotia Sea; year-class II individuals were absent from Antarctic samples. In the notal zone of the western South Atlantic, fish aged 1–5 years were found. The existence of only one population in the region is a possible explanation of these findings: this population is divided into a pelagic stock of juveniles and sub-adults which occur in the offshore waters of the western South Atlantic and benthopelagic stocks of adults distributed over the slope regions off Argentina, South Georgia and Antarctic archipelagos.
The computed values of K (von Bertalanffy growth) were 0.48, 0.41 and estimated total annual instantaneous mortality rates (Z) were 0.45, 0.67, and 0.70 for South Georgia, South Shetlands and notal zone of western South Atlantic stocks, respectively.     

海州湾秋季小眼绿鳍鱼摄食习性的空间异质性

研究海州湾小眼绿鳍鱼摄食习性的空间异质性,对于海州湾食物网构建和资源保护具有重要意义。根据2011及2013-2016年秋季在海州湾海域进行的渔业资源底拖网调查数据,结合小眼绿鳍鱼（Chelidonichthys spinosus）的空间分布特征及其胃含物样品的分析结果,研究了海州湾小眼绿鳍鱼的摄食热点海域及其摄食习性的空间异质性。结果表明,小眼绿鳍鱼是海州湾秋季底层鱼类群落中的优势鱼种,且各年均主要分布在海州湾35 °N附近及以北海域。细螯虾（Leptochela gracilis）、戴氏赤虾（Metapenaeopsis dalei）和疣背宽额虾（Latreutes planirostris）是小眼绿鳍鱼最重要的三种饵料生物。研究发现,海州湾小眼绿鳍鱼的摄食热点海域主要集中在30 m等深线附近,且尚未呈现出明显的年间变化趋势。根据各站位小眼绿鳍鱼食物组成的相似性,将调查海域划分为两个区域,即近岸区和远岸区,近岸区小眼绿鳍鱼的体长和体重均显著小于远岸区（P < 0.05）,小眼绿鳍鱼在近岸区主要摄食细螯虾和疣背宽额虾,在远岸区则主要摄食戴氏赤虾。近岸区小眼绿鳍鱼的空胃率显著小于远岸区（P < 0.05）,条件指数显著大于远岸区（P < 0.05）,平均胃饱满指数大于远岸区,但尚未呈现出显著差异（P > 0.05）,表明海州湾秋季小眼绿鳍鱼的摄食习性存在明显的空间异质性。     

Diel variability in catch rate of juvenile flatfish on two small nursery grounds (Port Erin Bay, Isle of Man and Porto Pirn Bay, Faial, Azores)

Variation in beach seine catches was examined in two juvenile flatfish populations (Port Erin, Isle of Man and Porto Pirn, Azores) to determine the importance of diel cycles while controlling for tidal rhythmicity. At Port Erin sampling was undertaken at each low water on consecutive days over a 2-week period in May/June and September 1991. There was no periodicity in the catches of plaice ( Pleuronectes platessa ) in May/June, but in September catches were higher at night. Other flatfish species ( Limanda limanda, Pleuronectes flesus, Scophthalmus maximus and S. rhombus ) sampled at Port Erin were nocturnal. At Porto Pirn, Azores, fish were sampled over 24 h each month from July 1989 to June 1990 and at each low water over a 2-week period in July 1991. The only flatfish species present was Bothuspodas , which had a diurnal pattern in catches over a 1-year period. Sampling at low water in July gave high catches at both midnight and midday.     

Effects of medium composition on the recovery of bacteria from sea water

Water samples were collected from offshore and inshore localities at various depths off the Connecticut coast over a two-year period. Spread plates for bacterial counts at 20 °C were made on a variety of complex solid media. Counts on Difco-Marine Agar were controls in all cases with counts on test media related to these in ratio form. Initially, nine media were used and represented some from the literature as well as personal formulations. Differences between inshore and offshore samples were greatest with media containing the highest peptone concentrations. Two media containing the peptones Gelysate and Trypticase showed the highest overall counts. A second phase concerned a comparative study of these peptones varying in concentration from 0.1 to 10.0 g/l in a constant basal medium. None of the media invariably gave counts greater than the control, but peptone concentrations of 10.0 and 5.0 g/l resulted in the lowest comparative counts. Considering all samples, peptone levels of 0.1 and 1.0 g/l showed the highest counts. Counts for both inshore and offshore water samples decreased as peptone concentration increased. Qualitatively, high peptone media showed large, mucoid, confluent colonies which made the counting of smaller ones difficult. Pigmented colonies were more frequent on low peptone media. Bacteria were isolated from all media and from all stations; the percentage of various groups varied with peptone concentration and source of sample.Media containing three fish peptones in varying concentrations have also been investigated. None produced overall counts greater than Difco-Marine Agar and counts decreased with increasing peptone levels: there was a trend towards higher counts in offshore waters with fish extracts. Quantitative and qualitative aspects of the work are discussed.     

Diel distribution patterns of fishes in a temperate large lowland river

During the day, juveniles and typical inshore species in the lower Oder River, Germany, inhabited the littoral (0·05–1·50 m deep) while potamal species inhabited the mid‐channel (40–100 m from the banks). During the night, two behavioural groups were distinguished: 1) potamal species and large individuals of other species, moved from offshore to the littoral, and 2) nocturnal foraging species, became active and increased in inshore and offshore habitats. Inshore, the most significant differences at night was the increasing density of silver bream Blicca bjoerkna increasing both total biomass and total length of fishes caught. Offshore, the increasing density of whitefin gudgeon Gobio albipinnatus at night was most significant. Additional night electrofishing improved the assessment of the abundance, age and size structure of typical potamal fish species. It should be incorporated in large river fish monitoring programmes.