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.     

Notes on helminth parasites of the whiting Odontogadus m. merlangus (L.) from the northern Irish Sea

In an examination of 1352 whiting from the Irish Sea 13 helminth species were discovered. One species, Scolex polymorphus Rudolphi, was a new species associated with whiting and 7 other species were new species for whiting from the Northern Irish Sea. The species of the digenean genus Podocotyle found in whiting is probably an ecotype of P. atomon. It was concluded that the bothridial structure of 5. polymorphus cannot be used for diagnostic purposes nor to determine early and late stages of the larvae. The number of Diclidophora merlangi Kuhn (Monogenea) from each monthly sample with eggs in the uterus is directly proportional to temperature, but egg production under experimental conditions was greatest at 6° C. Several theories are proposed to explain these apparently contradictory observations. The life-history of the digenean Stephanostomum pristis Looss, appears to be unusual in that the 2nd intermediate host may be planktonic. The nematode Contra caecum clavatum Rudolphi is found both as larvae and adults but larvae comprise the greater part of the worm population. The discovery of small stage II larvae in the stomach of whiting supports the theory that only one intermediate host is necessary for the development of Contmcaecum . There were significantly more female C. clavatum than male but a 1: 1 sex ratio is demonstrated by the acanthocephalan Echinorhynchus gadi Muller. Early and late forms of the plerocercoid of Grillotia erinaceus Van Beneden are identified. The early form occurred predominantly in the young whiting.     

The fish populations in inshore waters of the West Coast of Scotland. The distribution, abundance and growth of the whiting (Merlangius merlangus L.)

The whiting ( Merlangius merlangus ) is an important commercial species from the West Coast of Scotland. This paper describes the distribution, abundance, age composition and growth of juvenile whiting which are found in the inshore areas and sea lochs. No spawning was observed in the areas and it is assumed there was an active migration of whiting from the open sea. They were first caught by the bottom trawl in July, reached maximum abundance in November and December and thereafter declined in numbers until few remain by early summer. An exception to this occurs in Loch Etive and possible explanations for the fact that whiting tend to remain for longer periods and grow at a slower rate in this loch are discussed.     

Determination of age and growth ofBuccinum undatum L. (Gastropoda) off Douglas,Isle of Man

Age and growth ofBuccinum undatum off Douglas (Isle of Man, U.K.) were studied using four independent methods: length-frequency analyses (LFA), operculum analysis (OA), markrecapture experiment (MRE) and laboratory rearing (LR). Within the 16-month period between February 1989 and June 1990, only the January 1990 sample showed histograms allowing possible age group determination. Among the several length frequency analyses applied to this sample, the growth analysis program MIX calculated thatBuccinum reaches mean lengths of 28.5, 45.8, 59.9, 71.5 and 81.0 mm at the end of its first, second, third, fourth and fifth year, respectively, with an asymptotic length (L_∞) of 123.8 mm and Brody growth coefficient (K) of 0.20. Whilst the results from the LFA were supported by those from the OA and the MRE, growth in the laboratory differed; however, this was expected. Both K and L values found in this study are higher than those in two previous studies undertaken forBuccinum in northeastern England and northern France.     

Estimation of the density ofBuccinum undatum (Gastropoda) off Douglas,Isle of Man

The density of the common whelk (Buccinum undatum L.) off Douglas, Isle of Man, was determined by four methods: (1) pot sampling, (2) diving, (3) mark-recapture experiment, and (4) underwater television. Although the values obtained by these methods were comparable, the last two methods yielded overestimations ofBuccinum density. The results from diving survey and from pot sampling showed a good agreement, indicating that pot sampling can be used to determine the density of the common whelk, provided a good estimate of the pot attraction area is available. The range of whelk density between February 1989 and August 1990 resulting from pot sampling was between 0.08 and 0.38 individuals m⁻². The temporal fluctuations of the whelk densities are discussed in detail.     

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.     

Gastric digestion and nutrient absorption along the alimentary tract of whiting (Merlangius merlangus L.) fed on natural prey

Studies on the digestion process in fish can elucidate some aspects of nutritional physiology. The movements of food items in the alimentary tract are observed using X‐radiography techniques, and nutrient absorption along the alimentary tracts (expressed as relative percentage absorption gradient) is calculated based on the ash contents of adjacent samples. Apparent digestibility coefficient (ADC) values for protein (80–94%), lipid (90–97%), carbohydrate (80.5%) and energy (85–96%) calculated from laboratory‐fed whiting were comparable with those for other fish fed suitable diets. Considerable proportions of all nutrients were absorbed in the short region (anterior intestine/pyloric caeca) but active absorption continued for all nutrients in transit along the longer middle and posterior intestinal segments. In wild whiting samples, the estimated ADC values were protein (65%), lipid (81%) and energy (65%) in passage from the stomach to the rectal region. It was not possible to ascertain the prey in intestinal samples, which probably contained a mixture of species. Sprats and brown shrimps probably dominated the diet, based on biochemical analysis of stomach contents, but polychaetes and other crustaceans could have made a minor contribution.     

The infection dynamics and dispersion pattern of Lernaeocera branchialis L. on 0+ whiting (Merlangius merlangus L.) in the Oosterschelde (SW Netherlands)

Size and structure of the Lernaeocera branchialis population infecting 0+ whiting in the Oosterschelde were studied during 1989. Two periods of successful transmission were distinguished. The first transmission wave occurs in late spring when the post-larval whiting enter the Oosterschelde. A second wave occurs in autumn. This pattern in the infection dynamics is possibly related to seasonal variations in spatial overlap of the intermediate ( Platichthysflesus ) and the final host ( Merlangius merlangus ). The dispersion pattern of Lernaeocera branchialis within the whiting population can be described by the Poisson distribution. Possible explanations for the observed dispersion pattern are given. Evidence is presented that the rejection of pennella larvae is a key mechanism determining the abundance of L. branchialis in whiting. The potential impact of parasite-induced host mortality on population size and dispersion pattern of the parasite is discussed.     

Formation of parasite fauna in the bullhead (Cottus gobio L.) (Pisces: Cottidae)

The formation of parasite fauna in the bullhead Cottus gobio L. in different water bodies was examined. The largest number of parasite species including specific parasites was observed in the Onega and Ladoga lakes. It is suggested that the host and their parasites migrated namely from these water bodies to other part of the range of the bullhead.     

Seasonal changes in the common dab, Limanda limanda (L.) in Isle of Man Waters

Otolith accretion was greatest in summer when opaque bands were laid down and slowest in winter when hyaline rings were formed. Food intake was minimal in winter and maximal in summer. Liver weight was high in summer and winter and low in spring after spawning. Growth in length was higher in summer than winter. Gonad weight was greatest in winter for both sexes. Spawning occurred from February to April. After spawning males recovered earlier than females and testes ripened earlier than the ovaries. From winter to summer, the sea temperature increased from 7.5–13.0°C; the day length from 7–17h; and the salinity varied from 34.07−34.36%.     

The parasite fauna of cod (Gadus morhua L.) in Balsfjord,North Norway

Summary Samples of cod from Balsfjord, a subarctic fjord in North Norway, were collected and the fauna of macro-parasites was classified zoogeographically. The results revealed an impoverished and to a large extent boreal parasite fauna compared with that of cod from the Barents Sea. Because of the last glaciation Balsfjord is a relatively young ecosystem, and the silled entrance surrounded by an archipelago also makes the fjord a rather isolated system. This together with its small size may be important factors in explaining the character of its parasite fauna. The colonization by boreal parasites of both the Barents Sea and Balsfjord probably reflects the direction of the main currents.     

A new species of Callinera (Nemertea, Anopla, Palaeonemertea) from the Isle of Man

Callinera monensis sp. n., from Derbyhaven Harbour in the Islc of Man, is described and illustrated. The anatomy of the species is compared and contrasted with that of the other known members of the genus, Callinera buergeri Bcrgcndal and C. buergeri f. grandis Bergendal, from Scandinavian waters; f. grandis is afforded separate specific status as C. grandis Bcrgcndal.     

The basis of food selection in some estuarine fishes. Eels, Anguilla anguilla (L.), whiting, Merlangius merlangus (L.), sprat, Sprattus sprattus (L.) and stickleback, Gasterosteus aculeatus L.

The factors influencing the selection of food by eels, Anguilla anguilla, whiting, Merlanglus merlangius, sprat, Sprattus sprattus, and stickleback, Gasterosteus aculeatus have been investigated by analysing collections made in the Severn Estuary for 1 year. Non–migratory (yellow) eels measuring from 19–5–56–5 cm in length fed mainly on either the decapod Crangon vulgaris or on the mysid Neomysis integer during the warmer months but ceased to feed in the winter. Whiting measuring between 2–5 and 15 cm fed almost exclusively on C. vulgaris, N. integer and the sand goby, Pomatoschistus minutus. Sprats fed chiefly on either the arnphipod Gammarus salinus or N. integer. Sticklebacks seldom contained any food in their stomachs despite the presence of large quantities of suitable prey and the high level of hunting efficiency. Gammarus salinus, although normally abundant in the environment, was usually ingested in disproportionately small quantities by all fishes except sprats reflecting its concealment among floating weeds and a selection against small (less than 1 cm) organisms. Because of the limitations of size and the unusually efficient escape reaction of larger animals, only young representatives of Crangon vulgaris were captured. The isopod Eurydice pulchra was rarely eaten by any of the fishes even though it was common in the environment. Burrowing polychaetes, mainly Nereis diversicolor, were never utilized possibly due to the difficulty involved in removing these organisms from the substrate. Neomysis integer was the most frequently consumed organism. Although the average length of prey ingested by the whitings increased with the size of fish, this was not the case for the other species. The proportion of non–feeding eels and the dry weight of stomach contents of this species depended on the temperature of the water but were not related to the availability of prey and tidal conditions whereas the feeding of whiting could not be related to any environmental parameter.     

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.     

The status of the burbot Lota lota (L.) (Gadidae) in Britain

Records of burbot Lota lota (L.) captures from the early nineteenth century to the present have been gathered and arranged watershed by watershed in chronological order. Most are from eastward-flowing river systems from Durham southwards to the Great Ouse, but a few records from westward-flowing systems are considered. In many areas the records imply a decline of burbot numbers and distribution during the present century, though burbot may never have been more than locally abundant. Local over-fishing, pollution and habitat changes are considered the most likely causes of decline. Conservation measures seem desirable.     

Characterization of the bacterial community associated with the surface and mucus layer of whiting (Merlangius merlangus)

The bacterial community inhabiting the mucus layer and surface of whiting was examined to determine whether the bacteria present are a reflection of the surrounding water or an indigenous bacterial flora is present. The outer mucus, mouth mucus and gut of four whiting harvested from a site in the Irish Sea and the surrounding water were examined by terminal restriction fragment length polymorphism (tRFLP) analysis of the 16S rRNA gene and clone library construction. The water community was the most diverse, with only a small number of shared water-mucus phylotypes present. The bacterial flora associated with the outer mucus layer were more diverse than that of the mouth mucus and gut. All three mucus layers were characterized by the presence of a dominant phylotype, identified as clone wom-1, highly similar to Photobacterium iliopiscarium. In addition to other Photobacterium phylotypes, members of the CFB and Clostridia groups were also detected. Subsequently, whiting from 11 different sites along the east and south coast of Ireland were compared by tRFLP analysis. Strikingly, the mucus layer of whiting at all sites was characterized by the presence and dominance of a TRF corresponding to the clone wom-1 which was virtually absent from the water column.     

Seasonal and regional infestation characteristics of three ectoparasites of whiting, Merlangim merlangus L., in the North Sea

The colonization by both resident and migrating spawner populations of brown trout and the characteristics of resident and migrating juveniles derived from the two populations have been studied in a brook and its tributary over 4 years. Resident trout spawns mainly in the upstream part of the brook and migrating trout in the downstream part. There are density and growth variations for the two age classes (0+ and 1 +) of juveniles in autumn according to the year and the environment. In the brook, the population of 0 + fish increases from downstream to upstream while the density of other age classes decreases. The migrating juvenile population of the brook changes annually and consists mainly of 1 s (one summer) individuals coming from the upper part. These individuals migrate generally in autumn and winter while young trout produced in the middle and downstream parts of the brook migrate mainly in the spring. The emigration process of the 0 + population decreases markedly from upstream to downstream and appears to be independent of the autumn length and sex ratio. In the tributary, most trout are 0+ years old, the population structure is different, and no migrating fish is observed. The results are discussed and a colonization strategy of the brown trout population in this brook is suggested.     

Observations on the occurrence of Diclidophora merlangi (Trematoda: Monogenea) on the gills of whiting, Gadus merlangus

Diclidophora merlangi is a common parasite of whiting in the Irish Sea. The incidence of infection over an 18-month period of study varied between 43-59%. The majority of flukes in single worm infections are found on the 1st gill arch, although in infections of higher intensity increasing numbers of parasites are found on the remaining arches. The factors which may influence the distribution of Diclidophora on the host gills are discussed.     

The parasite fauna of <Emphasis Type="Italic">Arctogadus glacialis</Emphasis> (Peters) (Gadidae) from western and eastern Greenland

In all 155 specimens of the high Arctic codfish Arctogadus glacialis examined for metazoan parasites, 55 specimens were from southern and northern Baffin Bay, western Greenland, and 100 specimens from north-eastern Greenland and Scoresby Sound. A total of 20 parasite taxa were recorded. A new myxozoan Gadimyxa arctica was found in southern Baffin Bay and Scoresby Sound. The gadid myxozoan Zschokkella hildae, the digeneans Gonocerca phycidis and Lecithaster gibbosus, the gill copepod Haemobaphes cyclopterina and third-stage larvae of the nematodes Anisakis simplex and Hysterothylacium aduncum were found in Scoresby Sound only. The digenean Hemiurus levinseni and third-stage larvae of the nematode Contracaecum sp. were found at all four stations. The nematodes Ascarophis spp. were found at three stations. The parasite fauna of A. glacialis from Scoresby Sound was very similar to that of 50 specimens of the closely related Boreogadus saida from the same area.     

Age and growth of Trisopterus luscus (Linnaeus, 1758) (Pisces,Gadidae) off the coast of Asturias

The age and growth of an Asturian population of the bib Trisopterus luscus L. were studied based on 990 bibs from monthly catches from October 1986 until October 1988.Using the estimates of age taken from otolith readings, it was possible to construct a growth curve for the whole range of ages and demonstrate that most growth takes place during the first two years of life. The maximum age was found to be 5 years. The largest fish caught during the investigation measured 430 mm in standard length.The different growth rates of males and females show that in most cases the mean standard length of females was equal to or greater than that of the males.