Electrophoretic study of myosin isoforms in white muscles of some teleost fishes

1. White skeletal muscle myosin of four marine teleost fish species (cod, blue whiting, Norway haddock, and spotted wolf-fish) was analyzed by native, SDS-PAGE, and 2-dimensional electrophoresis. 2. Four types of native myosin were present in cod, blue whiting and Norway haddock. The second fastest migrating form was predominant. 3. Myosin from spotted wolf-fish also resolved into four forms. The fastest migrating form was hardly noticeable. The other three were present in apparently similar amounts. 4. In the myosin from each species there were three types of light chains. The pattern of light chains was species specific. 5. Apparently, there was only one type of heavy chain in myosin from cod, Norway haddock and spotted wolf-fish. One preparation of cod showed an extra band of higher electrophoretic mobility than the main band. In blue whiting we found two bands present in approximately equal amounts.     

Predation on northern shrimp (Pandalus borealis) by three gadoid species

Northern shrimp (Pandalus borealis) is targeted by commercial fisheries, but is also an important prey in the marine food web. In this study, stomach content data were used to study predation on shrimp by three gadoid species, cod (Gadus morhua), haddock (Melanogrammus aeglefinus) and whiting (Merlangius merlangus), in six inshore areas around Iceland. The results showed that shrimp was more important in the diet of cod compared with the other two predators. However, the overall predation pressure was similar for cod and haddock due to the high abundance of haddock. Therefore, even though shrimp is not the primary source of food for haddock, this species can have a substantial effect on shrimp stocks when haddock abundance is high. In addition, while cod and haddock did not select for any particular size of shrimp, whiting seemed to preferentially target juvenile shrimp. The results suggest that due to the overall effects of these three predators on shrimp stocks, gadoids need to be included in the management of shrimp stocks as predation is one of the major drivers in the development of this important prey stock.     

The genera Ceratomyxa Thélohan, 1892, Leptotheca Thélohan, 1895 and Sphaeromyxa Thélohan, 1892 (Myxosporea: Bivalvulida) in gadid fish of the Northeast Atlantic

The gall-bladders of four species of gadid fish from the North Sea and Norwegian waters were examined for myxosporeans. The host species were cod Gadus morhua L. (350 examined), haddock Melanogrammus aeglefinus (L.) (592 examined), saithe Pollachius virens (L.) (205 examined) and whiting Merlangius merlangus (L.) (368 examined). Four species of myxosporeans are redescribed from these fish. Ceratomyxa arcuata Thélohan, 1892 was the most common species and was found in whiting (42.8%) and cod (0.6%). Leptotheca informis Auerbach, 1910 was found only in whiting (6.5%). L. longipes Auerbach, 1910 was found only in haddock (6.2%). Sphaeromyxa hellandi Auerbach, 1909 was found in haddock (9.1%) and whiting (0.3%). None of the saithe examined, and no cod or haddock from Norwegian waters, was infected with these myxosporeans. All four species appear to have distributions limited to the Northeast Atlantic, with S. hellandi having a more northern distribution than the other three. The validity of reports of C. arcuata, L. informis and L. longipes from outside this area is discussed.     

Effects of survey scale and water depth on the assessment of spatial distribution patterns of selected fish in the northern North Sea showing different levels of aggregation

Geostatistics was employed to investigate spatial structuring of herring, cod, dab, haddock and whiting at different spatial scales in the northern North Sea. Additionally, a structural analysis of the maximum water depth was carried out to assess habitat associations of fish. Linear, spherical, exponential and Gaussian models were fitted to the semivariograms, showing clear spatial autocorrelations. At the smaller scale, spatial structuring was weak for haddock, herring and dab, increasing at the greater spatial scale, with the exception of whiting. Mean catch rates, estimated classically and geostatistically, were in good agreement. Corresponding variances were clearly reduced at both spatial scales, when accounting for spatial distribution of the fish. At the greater survey scale a high level of habitat association was detected for haddock and whiting, while a poor habitat association was found for cod, dab and herring. The smaller scale seems to be the threshold at which spatial structuring of “cpue” could have marked influence on estimation error. Thus, survey scale is important when analysing spatial patterns and estimating mean biomass indices, and a sound analysis of relations in spatial structuring of fish and habitat conditions is essential to derive more precise estimates.     

Biochemical changes occurring during final maturation of eggs of some marine and freshwater teleosts

Biochemical changes which occur during post-vitellogenic meiotic maturation of oocytes were investigated by measuring the concentrations of various phosphorus-containing fractions of the ovaries and mature eggs of four marine species with pelagic eggs, plaice, Pleuronecles platessa , cod, Gadus morhua , haddock, Melanogrammus aeglefinus , and whiting, Merlangius merlangus , and three freshwater species with demersal eggs, rainbow trout, Salmo gairdneri , pike, Esox lucius , and powan, Coregonus lavarelus . In the former group, protein phosphate was deposited at normal vertebrate levels in the ovaries during vitellogenesis but was exhausted during maturation, its decrease correlating with the uptake of water which rendered the mature egg buoyant in sea water. In plaice, phospholipid phosphate declined slightly during maturation, while inorganic phosphate increased by an amount slightly less than that which disappeared from the protein fraction. No such changes occurred on maturation in these three fractions in the freshwater species, in which little or no water uptake occurred. In plaice, the approximately five-fold increase in the water content of the oocyte was accompanied by a corresponding five-fold increase in the amount of potassium, the major inorganic cation of the oocyte. These pelagic eggs appear to be unique among the eggs of vertebrates in their high water content ( c . 92%) and in the fact that the protein phosphate is almost entirely utilized before fertilization, while, in those freshwater fishes and other oviparous vertebrates that have been examined, the egg is of much lower water content (50–70%) and most of the protein phosphate, like the other major yolk constituents, is used during embryonic growth. This utilization at such an early stage in the life cycle constitutes an extreme example of heterochrony.     

Observations on the food and diel feeding behaviour of pelagic O-group gadoids in the northern North Sea

The diets and diel feeding behaviour of six O-group gadoid species are described, the cod Gadus morhua (L.), the haddock Melanogramus aeglefinus (L.), whiting Merlangius merlangus (L.), saithe Pollachius virens (L.), Norway pout Trisopterus esmarkii (L.) and the blue whiting Micromesistius poutassou (R.). There were differences, in the main food groups selected by each species with respect to the type, size and number. The main prey consumed did not vary with depth. Cod, saithe and Norway pout had only one period of feeding activity whereas haddock and whiting apparently had two. The diets of haddock and whiting varied in association with these two periods. It is suggested that the differences between the diets were the result of each species having a different feeding behaviour which reflects that adopted in adult life.     

The staining of fish otoliths for age determination

Attempts were made to find methods for the staining of fish otoliths which would give results comparable to those of the Christensen burning technique. A variety of different histological stains and otoliths of different species were experimented with. Otoliths of sole, turbot, brill and scad gave best results when sectioned and stained in acidified Neutral Red, whereas those of cod, hake, whiting, plaice and grey mullet showed up the annuli better when dyed in aqueous Aniline Blue or Toluidine Blue and then sectioned. Small, translucent otoliths such as those of pelagic species may be enhanced by staining in Eosin Y.     

TaqMan DNA technology confirms likely overestimation of cod (Gadus morhua L.) egg abundance in the Irish Sea: implications for the assessment of the cod stock and mapping of spawning areas using egg-based methods

Recent substantial declines in northeastern Atlantic cod stocks necessitate improved biological knowledge and the development of techniques to complement standard stock assessment methods (which largely depend on accurate commercial catch data). In 2003, an ichthyoplankton survey was undertaken in the Irish Sea and subsamples of 'cod-like' eggs were analysed using a TaqMan multiplex, PCR (polymerase chain reaction) assay (with specific probes for cod, haddock and whiting). The TaqMan method was readily applied to the large number of samples (n = 2770) generated during the survey and when combined with a manual DNA extraction protocol had a low failure rate of 6%. Of the early stage 'cod-like' eggs (1.2-1.75 mm diameter) positively identified: 34% were cod, 8% haddock and 58% whiting. As previous stock estimates based on egg surveys for Irish Sea cod assumed that the majority of 'cod-like' eggs were from cod, the TaqMan results confirm that there was probably substantial contamination by eggs of whiting and haddock that would have inflated estimates of the stock biomass.     

Isolation of twenty low stutter di- and tetranucleotide microsatellites for population analyses of walleye pollock and other gadoids

Fourteen tetra- and six dinucleotide microsatellites, which exhibit minimal stuttering following amplification via PCR were developed from walleye pollock Theragra chalcogramma . Most of these loci were isolated from a library enriched for tetranucleotide microsatellites by hybridization of genomic DNA to (gata)₇ oligonucleotides bound to streptavidin-coated paramagnetic beads. The average heterozygosity of these loci is ∼80%, and ranges from 53–95%. Mendelian inheritance was confirmed in five families, each consisting of a minimum of 10 or more offspring. Primer sets for all 20 loci were also evaluated in Arctic cod Boreogadus saida , Pacific cod Gadus macrocephalus , Pacific tomcod Microgadus proximus , sa.ron cod Eleginus gracilis , Pacific hake Merluccius productus , Atlantic cod Gadus morhua , haddock Melanogrammus aeglefinus , blue whiting Micromesistius poutassou , and European hake Merluccius merluccius . In each of these species, 3–19 primer sets amplified variable microsatellite loci. These loci, which exhibit little stutter and moderate to high variability, should be useful population markers in pollock and other gadoid fishes.     

Trends in abundance of benthic and demersal fish populations of the lower Forth Estuary, East Scotland, from 1982–2001

The benthic and demersal fishes of the lower Forth Estuary, east Scotland, were sampled by Agassiz trawling from January 1982–December 2001. Three stations of varying distance from the mouth of the estuary were trawled at high and low water in 5 months of each year, a total of 30 trawls per annum using the same ship and net design throughout. Of 30 species collected over this period, whiting Merlangius merlangus was the most abundant, followed by eelpout Zoarces viviparus , pogge Agonus cataphractus , flounder Platichthys flesus and plaice Pleuronectes platessa . The 10 most abundant species accounted for 97·8% of the total benthic-demersal fish abundance. There was no trend in total annual species richness sampled, though total annual abundance of fishes captured decreased significantly from 1982–2001. This was largely caused by significant declines in abundance of whiting and eelpout. Fatherlasher Myoxocephalus scorpius showed a significant linear increase. None of the seven remaining most abundant species exhibited significant trends in abundance. Decline of eelpout may be attributable to increases in water temperature adversely affecting reproductive success. This is suggested by a significant negative correlation of mean annual abundance with January bottom temperature in the previous year.     

Distribution and diet of 0-group cod (<Emphasis Type="Italic">Gadus morhua</Emphasis>) and haddock (<Emphasis Type="Italic">Melanogrammus aeglefinus</Emphasis>) in the Barents Sea in relation to food availability and temperature

Distribution of 0-group cod (Gadus morhua) and haddock (Melanogrammus aeglefinus) in August–September 2005 and 2006 was mainly restricted to the Atlantic waters of the western and central areas of the Barents Sea. The main distribution of 0-group fish overlapped largely with areas of high biomass (>7 gm⁻² dry weight) of zooplankton. The copepod Calanus finmarchicus and krill Thysanoessa inermis, which are dominant zooplankton species in both Atlantic and boreal waters of the Barents Sea, were the main prey of 0-group cod and haddock. The main distribution, feeding areas and prey of 0-group cod and haddock overlapped, implying that competition for food may occur between the two species. However, though their diet coincided to a certain degree, haddock seems to prefer smaller and less mobile prey, such as Limacina and appendicularians. As 0-group fish increased in size, there seems to be a shift in diet, from small copepods and towards larger prey such as krill and fish. Overall, a largely pelagic feeding behaviour of 0-group cod and haddock was evident from this study.     

Resource sharing among cod, haddock, saithe and pollack on a herring spawning ground

Cod Gadus morhua , haddock Melanogrammus aeglefinus , pollack Pollachius pollachius and saithe Pollachius virens were abundant fishes on herring Clupea harengus spawning grounds o. southwestern Norway. Their diets were species specific and ontogenetic changes were similar to patterns observed in other areas, indicating both inter- and intraspecific resource sharing. However, strong interspecific diet overlap occurred when cod and pollack preyed upon sandeel Ammodytes marinus , and when all the gadoids fed on herring eggs during the herring spawning season in the spring. These prey items were very abundant and the extensive diet overlap may not reflect strong competitive interaction.     

Otolith oxygen and carbon stable isotopes in wild and laboratory-reared plaice (Pleuronectes platessa)

The relationship between water temperature, growth rate, and otolith isotopic ratios was measured for juvenile plaice (Pleuronectes platessa) reared at two temperatures (11 and 17°C) and two feeding regimes (1 and 3 prey items·ml^?1). The otolith isotope ratios in individual fish ranged from ?2 to ?4 for carbon isotope ratios (δ¹³C) and from 0.2 to 1.9 for oxygen isotope ratios (δ¹⁸O). The otolith oxygen isotope ratios were significantly affected by water temperature, but not by feeding level, and there were no significant synergistic effects. The fractionation of oxygen isotopes during otolith growth was independent of individual growth rate. Carbon isotope ratios were not significantly affected by food ration or water temperature, but were related to fish growth rate. The carbon isotope ratios were negatively correlated with fish length in the colder water treatments, and tended to increase with fish length in the warm water treatments. The laboratory-determined relationship between otolith oxygen isotope ratio and water temperature was applied to individuals of five species (plaice, cod, whiting, haddock, gurnard) collected in a single trawl sample. The otolith derived temperatures often overestimated measured water temperatures. The difference between real and estimated water temperatures varied between species, and the closest fit was for field-caught plaice.     

Fisheries management and conservation in the Irish Sea

The Irish Sea ia a relatively small, enclosed sea area which is subject to a wide range of human uses including navigation, oil terminals, dumping of sewage and industrial sludge, cooling for nuclear power stations, gravel extraction, gas and oil prospecting and fishing. Commercial fishing is affected by the other uses and at the same time it provides a means of monitoring their effects on a part of the ecosystem. Regular samples taken from fish markets provide a long series of age-composition data of the main commercial species — cod, whiting, plaice and sole — from which population changes can be assessed. More recently groundfish trawl surveys have been carried out to provide more detailed information on the distribution of all demersal fish species seasonally and in relation to area, depth and sediment type. Advice on the management of commercial fish species is prepared by a working group of the International Council for the Exploration of the Sea (ICES), and is based mainly on analytical single-species models. There are obvious shortcomings of such models in an area of mixed fishery and high diversity such as the Irish Sea. The objectives adopted in these models and in fisheries management generally are examined critically in relation to the possible aims of conservation.     

The role of sense organs in the feeding behaviour of juvenile sole and plaice

An infra-red video recording system was used to observe and compare the feeding activity of juvenile sole and plaice. Experiments in light or dark and chemical ablation of the neuromasts with streptomycin sulphate allowed all or a limited set of senses to be used by the fishes. Both species were able to feed on dead prey when only chemical stimuli were available. Plaice showed a greater dependence on vision for feeding but sole relied principally on chemoreception and mechanoreception. When any one sense was removed plaice became less active whereas sole became more active.     

Interspecific Resource Competition Effects on Fisheries Revenue

In many fisheries multiple species are simultaneously caught while stock assessments and fishing quota are defined at species level. Yet species caught together often share habitat and resources, resulting in interspecific resource competition. The consequences of resource competition on population dynamics and revenue of simultaneously harvested species has received little attention due to the historical single stock approach in fisheries management. Here we present the results of a modelling study on the interaction between resource competition of sole (Solea solea) and slaice (Pleuronectus platessa) and simultaneous harvesting of these species, using a stage-structured population model. Three resources were included of which one is shared with a varied competition intensity. We find that plaice is the better competitor of the two species and adult plaice are more abundant than adult sole. When competition is high sole population biomass increases with increasing fishing effort prior to plaice extinction. As a result of this increase in the sole population, the revenue of the stocks combined as function of effort becomes bimodal with increasing resource competition. When considering a single stock quota for sole, its recovery with increasing effort may result in even more fishing effort that would drive the plaice population to extinction. When sole and plaice compete for resources the highest revenue is obtained at effort levels at which plaice is extinct. Ignoring resource competition promotes overfishing due to increasing stock of one species prior to extinction of the other species. Consequently, efforts to mitigate the decline in one species will not be effective if increased stock in the other species leads to increased quota. If a species is to be protected against extinction, management should not only be directed at this one species, but all species that compete with it for resource as well.     

Robertsonian polymorphism in plaice, Pleuronectes platessa L., and cod, Gadus morhua L., (Pisces Pleuronectiformes and Gadiformes)

Karyotypic analysis of plaice, Pleuronectes platessa L., and cod, Gadus morhua L., revealed that the chromosome numbers in both species vary but that chromosome arm numbers (NF) stay constant. The C-, Q- and R-banding patterns also confirmed that the population of plaice studied shows Robertsonian polymorphism. The tendency of reduction in chromosome number in fishes suggests that Robertsonian fusions play a role in karyotype evolution in fishes.     

Distribution of viral haemorrhagic septicaemia virus in wild fish species of the North Sea, north east Atlantic Ocean and Irish Sea.

A surveillance programme was initiated on the occurrence and distribution of viral haemorrhagic septicaemia virus (VHSV) in wild marine fish. Six research cruises were undertaken in an 18 mo period during 1997 and 1998, covering the North Sea, the Atlantic waters off the north and west coasts of Scotland and the Irish Sea. A total of 19,293 fish were sampled from 23 different species including cod, haddock, Norway pout, herring and sprat. Individual fish lengths were recorded and the fish were checked for lesions, haemorrhaging and other signs of disease. Pools of organ samples were taken for virus assay. The majority of fish sampled did not display clinical signs indicative of viral haemorrhagic septicaemia. A small number of cod were found with skin lesions and haddock with skin haemorrhaging. Of the 2081 organ and skin sample pools collected, 21 tested positive for VHSV by tissue culture and enzyme-linked immunosorbent assay. Seventeen of the isolates originated from Norway pout Trisopterus esmarkii, one from cod Gadus morhua (skin lesion), one from herring Clupea harengus, one from whiting Merlangius merlangus, and one from a previously unreported host species, poor cod Trisopterus minutus.