Eutrigla Research Articles

Effect on catch efficiency and bycatch by introducing an Excluder device in the trawl fishery for lesser sandeel (Ammodytes marinus).

Sampling of the North Sea trawl fishery for lesser sandeel (Ammodytes marinus) showed that 96% of the catch weight consisted of the target species, and experimental sea trials demonstrated that the observed small bycatch percentages of haddock (Melanogrammus aeglefinus), mackerel (Scomber scombrus) and grey gurnard (Eutrigla gurnardus) could be significantly lowered by inserting a netting-based sorting device, an Excluder, in front of the codend. The sandeel fishery is conducted with small meshes in the codend, due to the small size and elongated body shape of this species. It is not mandatory for sandeel trawls to have any other selection devices than the small-meshed codend, and this can potentially cause problems with bycatch of unwanted species, if these are abundant on the fishing grounds. Therefore, we sampled the catch composition in this fishery and further, we compared the capture efficiency and species composition of a standard trawl, and one fitted with an additional sorting device called the Excluder. Overall, results showed small percentages of bycatch in the trips sampled and during the trials, the excluder significantly reduced the bycatches of mackerel, grey gurnard, and haddock above certain sizes. For other bycatch species results were inconclusive due to wide confidence limits affected by low bycatch numbers during the trials. The overall capture efficiency for the target species was not affected by adding the excluder in the trawl except for a significant reduction for a few semi-centimetre groups of the largest sizes of the species. These results highlight the potential of the Excluder as a bycatch reduction tool in the sandeel fishery for situations where bycatch can constitute a problem.

The genome sequence of the grey gurnard, Eutrigla gurnardus (Linnaeus, 1758).

We present a genome assembly from an individual Eutrigla gurnardus (the grey gurnard; Chordata; Actinopteri; Scorpaeniformes; Triglidae). The genome sequence is 680.5 megabases in span. Most of the assembly is scaffolded into 24 chromosomal pseudomolecules. The mitochondrial genome has also been assembled and is 16.51 kilobases in length.

Long-term change in a North Sea inshore fish assemblage between 1899-1913 and 2018-2019

Marine communities have been impacted by human activities for centuries, yet historical data are rarely incorporated into modern conservation efforts and restoration targets. For inshore waters, survey data sets are typically lacking because they extend back by only a few decades, despite their ecological significance as nursery grounds for many fish species. We investigated long-term change in a demersal fish assemblage from inshore waters of the Northumberland coast (UK). We collated unique historical data (1899-1913) that were sampled using a wooden beam trawl during scientific trawling investigations, shortly after the onset of widespread mechanised trawling in the North Sea. Twelve decades later (2018-2019), we re-surveyed the same bays using a modern otter trawl. The results revealed marked declines in the abundance and diversity of the entire fish and flatfish assemblage as well as among individual species. Elasmobranchs and formerly abundant species such as grey gurnard Eutrigla gurnardus were completely absent in contemporary surveys, while dab Limanda limanda and plaice Pleuronectes platessa were the most dominant species in both periods. Changes were also detected in the size distributions of the entire fish and flatfish assemblages, with proportionally fewer large individuals recorded in contemporary surveys. These findings suggest that over a century of trawling and climate change, combined with pollution, habitat alteration and increased predation risk are likely contributors to changes in the inshore fish assemblage. This work provides further evidence of long-term decline in North Sea inshore waters and offers an invaluable benchmark for improving coastal ecosystem status.

Untangling the Derogenes varicus species complex in Scandinavian waters and the Arctic: description of Derogenes abba n. sp. (Trematoda, Derogenidae) from Hippoglossoides platessoides and new host records for D. varicus (Müller, 1784) sensu stricto.

Several studies have shown that the euryxenic trematode Derogenes varicus (Müller, 1784) represents a species complex. Four lineages have been designated (DV1-4) with the DV1 clade corresponding to D. varicus sensu stricto. Herein, we investigate newly collected specimens of D. varicus sensu lato from Scandinavian and Arctic waters using integrative taxonomy. The trematodes were collected from Melanogrammus aeglefinus, Eutrigla gurnardus, Trachinus draco, and Merluccius merluccius off the Atlantic coast of Sweden and from Hippoglossoides platessoides from Arctic Svalbard. 28S sequences of derogenids from Sweden were identical to D. varicus sensu stricto, confirming its euryxeny. The 28S sequences of Derogenes sp. from H. platessoides were identical to Derogenes DV2 and differed from D. varicus sensu stricto by 3% and from Derogenes DV3 by 2%. The 28S sequence divergences of Derogenes sp. from H. platessoides with D. ruber and D. lacustris were 3 and 10%, respectively. ITS2 and cox1 divergences between Derogenes sp. from H. platessoides and other Derogenes species/lineages were at levels of interspecific differences. The species from H. platessoides is described here as D. abba n. sp. We also examined the type material of Progonus muelleri (Levinsen, 1881), the type and only species of the genus Progonus, with redescription and designations of paralectotypes. Based on specimens from Theodor Odhner's collections at the Swedish Museum of Natural History, SMNH, Stockholm, we provide novel morphological and anatomical data for D. varicus sensu lato species complex. Lastly, we investigated Arthur Looss's "lost collection" of Trematodes at the SMNH and characterised a putative species Derogenes sp. "limula".

How an illuminated headline affects catches and species separation in a Celtic Sea mixed demersal trawl fishery

Installing artificial lights on fishing gear is increasingly being explored to alter the behaviour of fish during the capture process and modify selectivity. We investigated the effect of introducing artificial light on a commercial trawler operating in the English southwest mixed demersal fishery. Total catch and species vertical separation were compared and analysed in two identical separator trawls towed simultaneously. One trawl was equipped with blue LEDs along its headline, the other trawl served as a control to allow for pairwise catch comparison. Fishing trials were conducted at night and during the day. In the presence of lights, catches-at-length of haddock (Melanogrammus aeglefinus) were lower during the night and marginally higher during the day. Catches of grey gurnard (Eutrigla gurnardus), megrim (Lepidorhombus whiffiagonis) and whiting (Merlangius merlangus) were unaffected by lights. In terms of vertical separation, in the presence of lights, more haddock were retained in the lower codend during the day and night. Lights also increased the proportion of catches in the lower codend for grey gurnard, whiting and Northern squid (Loligo forbesii), but only during the day. This study shows there are species-specific reactions to artificial light during the trawl capture process and these reactions can be different between day and night. When reviewed with other studies, some common observations are identified, indicating that lights can change the behaviour of some species which normally rise inside the trawl during the capture process, such as haddock. The use of artificial lights offers an alternative method to modify trawl selectivity, by utilising species-specific reactions to light, and the ability to change the position and characteristics of the light, offers many avenues to investigate.

Internal injuries in marine fishes caught in beam trawls using electrical versus mechanical stimulations

Abstract To improve the ecological and economic sustainability in the Dutch beam trawl fishery, tickler chains were replaced by electrical pulse stimulation to drive common sole (Solea solea) out of the seabed. Because electrical stimulation may cause internal injuries, we quantified this risk by sampling fish species from commercial beam trawlers and recording spinal injuries and haemorrhages from X-radiographs and autopsy. To distinguish mechanically-induced and electrical-pulse-induced injuries, we compared injuries in ten species sampled from pulse (PUL) and tickler-chain (TCK) trawlers and four species sampled from PUL trawlers with the stimulus switched on or off. Co-occurrence of a major spinal injury and major haemorrhage at the same location was only observed in PUL samples, and were frequently (40%) observed in Atlantic cod (Gadus morhua) and in low numbers (0–2%) in whiting (Merlangius merlangus), grey gurnard (Eutrigla gurnardus), and greater sandeel (Hyperoplus lanceolatus), but not in flatfishes and other species. In cod, injury occurrence correlated with fish length, with lower probabilities for small fish. Major spinal injury or major haemorrhage occurrence in PUL (range: <1–16%) was lower than in TCK (range: <1–42%) in eight of the ten species studied. Population level consequences of pulse-induced injuries are considered negligible.

Changes in catch efficiency and selectivity in the beam trawl fishery for sole when mechanical stimulation is replaced by electrical stimulation

Beam trawl fisheries for sole are characterised by large amounts of unwanted bycatch (i.e. discards) consisting of fish below the Minimum Conservation Reference Size, unwanted fish due to low commercial value or lack of quota, and benthic invertebrates. In order to reduce the quantity of discards, a substantial part of the Dutch beam trawl fleet was allowed to replace the conventional tickler chain beam trawl (BT) with the pulse trawl (PT) on an experimental basis. The PT used electrical stimulation to immobilise and capture fish. Here we study whether pulse trawling reduced the amount of discards by comparing catch rates of landings and discards of BT and PT in the period 2009–2018 for a wide range of species. The PT caught (kg.km-2) significantly more marketable sized sole (Solea solea, 48 %), turbot (Psetta maxima, 8 %), brill (Scophthalmus rhombus, 28 %) and whiting (Merlangius merlangus, 95 %), and significantly less marketable sized plaice (Pleuronectes platessa, −16 %), cod (Gadus morhua, −32 %) and gurnards (−12 %). No significant difference was found for dab (Limanda limanda), gadoids, or rays and sharks. Among discards, the PT caught more undersized sole (27 %) and whiting (42 %) but less undersized plaice (−21 %), dab (−19 %) and grey gurnard (Eutrigla gurnardus, −31 %). The observed differences in species selectivity are discussed in relation to the response of fish to bottom trawl gear and the effects of pulse stimulation. For the benthic invertebrates Ophiuroidae, bivalves and crabs the PT caught fewer individuals (between −38 % and −57 %). No significant difference was observed in sea urchins and sea stars. Overall, this study shows that the transition from the BT to PT resulted in a 36 % decrease (95 % prediction interval: 31–42 %) in discards (kg.hour-1).

An ultrastructural focus on the buccal cavity of the grey gurnard Eutrigla gurnardus (Linnaeus, 1758): Adaptative dietary implications.

The current investigation represented the first anatomical description of the buccal cavity of the grey gurnard Eutrigla gurnardus. For the achievement of this study, 10 heads of mature fish were used for SEM examinations. The morphological characteristic appearance of the buccal cavity has shown several adaptations in relation concerning its feeding habits. The median fissure of the upper lip divided the upper lip into two halves, this fissure appeared to be formed from many micro-tubercles with numerous taste buds which aid in holding mucus secretion to the cell surface, help in mucus spread, and provide mechanical protection to the epithelium. Velum had two regions: median and peripheral region. The epithelium covering of the median region of the upper velum had dots-like epithelial protrusion that carrying numerous taste buds, meanwhile, the epithelium covering of the lower velum not carried taste buds but instead carried numerous small scales-like structures. The palate is divided into two semicircular regions by small region of microridges into the anterior and posterior region. The slightly bifid tongue had a median tubercle with numerous small taste buds on its dorsal surface. Concluded, these data were necessary to understand the adaptation of fish to its habitat and in developing a new and better method for fishing of this type of fish.

The complete mitochondrial genome of the spiny red gurnard Chelidonichthys spinosus McClelland, 1844 (Scorpaeniformes: Triglidae)

The spiny red gurnard, Chelidonichthys spinosus is a common marine economic fish species along the coast of China. In the present study, the complete mitochondrial genome of spiny red gurnard collected from the Yangtze Estuary was determined by next-generation sequencing (NGS). The mitogenome is a circular nucleotide 16,466 bp in length and has the typical vertebrate genome structure of 13 protein-coding genes, two ribosomal RNA genes, 22 transfer RNA genes, and two control regions (Origin of Heavy chain and Origin of Light chain). The termination associated sequence (TAS), the central conserved sequence block (central CSB), and the conserved sequence block (CSB) were detected in the control region. Phylogenetic analysis of C. spinosus places in a fully supported clade with C. kumu in a sister position to Eutrigla gurnardus. The complete mitochondrial genome sequence of the spiny red gurnard provides baseline genetic information for future studies on the molecular systematics and phylogeny of bony fishes in the Triglidae.

Spatiotemporal dynamics of predators and survival of marine fish early life stages: Atlantic cod (Gadus morhua) in the North Sea

Predation is one of the principle factors regulating the survival of early-life stages and recruitment success of marine fishes. Although challenging, it is important to understand how predation mortality varies in space and how this spatial variability affects the temporal dynamics of fish recruitment. We investigated the spatiotemporal variability in the magnitude of predation mortality and survival of Atlantic cod (Gadus morhua) in the North Sea by combining a Lagrangian individual-based model of cod early-life stages (eggs, larvae and age-0 juveniles) with an Eulerian representation of its fish predators based on field data collected quarterly from 1991 to 1997. The mean and variance (spatial and inter-annual) in survival of cod were different between simulations using homogeneous and heterogeneous spatial distributions of predators. Survival of cod through its early-life period was 1 order of magnitude higher in simulations using heterogeneous versus homogenous predator distributions, mainly due to reduced mortality of eggs and larvae in the former simulation. Our model predicted markedly different year-to-year changes in cod survival, when heterogeneous predator fields were implemented. In the heterogeneous simulation, Atlantic herring (Clupea harengus) and grey gurnard (Eutrigla gurnadus) emerged as the most important predators comprising, respectively, 68% and 13% of the predation mortality caused by 7 predators included in our study. A low (<0.1%) survival was predicted for cod progeny originating from known spawning grounds in the central and south-eastern North Sea while considerably higher survival (between 0.8 and 1%) was predicted for northern spawning areas and in the Southern Bight. Numerical sensitivity experiments indicated that seasonal and annual changes in the spatial distribution of predators were more important to the inter-annual variability in the modelled cod survival (52% of the mean survival) than annual changes in the biomass of predators (23%) and the variability of the North Sea hydrography (19%) with the relative importance of these factors depending on the life stage of cod. We argue that including spatial dynamics of predators will advance the predictive capacity of fish early-life stage models enabling more robust, science-based advice for spatially-explicit fishery management and marine spatial planning.

Population size estimation of chirp and grunt generating fish and mammals using cross-correlation based technique with three acoustic sensors

Passive acoustic monitoring has the potential to be a useful tool for population estimation of sound-producing fish and mammals (mostly whales). Previous work on population estimates of callers employed a simple cross-correlation technique with recordings from two acoustic sensors, and the current work extends the technique to two configurations of a 3-acoustic sensors array using two different sounds, i.e., chirps which is commonly generated by damselfish (Dascyllus aruanus), humpback whales (Megaptera novaeangliae), dugongs (Dugong dugon) etc., species, and grunts which is commonly generated by Japanese gurnard (Chelidonichthys kumu), Grey gurnard (Eutrigla gurnardus), gulf toadfish (O. beta), etc., species. We compared simulated results from this technique with values determined by theoretical approach. We have found that an increasing number of cross-correlation function (CCF) provide better results using this technique. However, the technique has some limitations including negligence of multipath interference, assuming the delays to be integer.

The influence of continuous lines of light on the height at which fish enter demersal trawls

Fishing trials were conducted to investigate the effect of continuous lines of light on the height at which fish enter demersal trawls. A two-level trawl, with a horizontal separator panel that either directs fish to go above the panel to one codend or to go below it to another, was fished. A side-emitting fibre optic cable, illuminated by a light emitting diode (LED), was used to provide a continuous distribution of light on the leading edge of the separator panel and on the fishing line. During autumn daytime trials the illuminated cable only influenced common dab (Limanda limanda). The panel height was also varied during these trials and more lemon sole (Microstomus kitt), plaice, long rough dab (Hippoglossoides platessoides), common dab and gurnards entered the trawl above the panel when the height of its centre section was constrained to 20 cm above the fishing line. During trials held at night, in spring, the illuminated cable significantly reduced the proportion of haddock (Melanogrammus aeglefinus), whiting (Merlangius merlangus), plaice (Pleuronectes platessa), common dab and gurnards (Eutrigla gurnardus and Chelidonichthys cuculus) that swim over the panel. It did not matter whether the illuminated line was attached to the leading edge of the separator panel or to the fishing line as there was no difference in how fish entered the gear between these cases.The results demonstrate how illuminated cables can be used to modify the height at which fish enter demersal trawls, direct them to different parts of the fishing gear and potentially improve the selective performance of trawl gears. They highlight that response to the panel will be species specific and may have seasonal and environmental dependencies.

Population biology of grey gurnard (Eutrigla gurnardus (L.); Triglidae) in the coastal waters of Northwest Wales

The grey gurnard Eutrigla gurnardus (L.) has been identified by ICES as a potential commercial species in the NE Atlantic with recommendations made to derive information on population biology for stock assessment purposes. However, data on the population biology of this species is limited. In this study, data on the age, growth and maturity of grey gurnard were collected by otter trawling in the coastal waters of northwest Wales and Eastern Anglesey. Total length (TL) of fish sampled ranged between 2.1–33.0 cm (male) and 1.9–36.9 cm (female) with the majority of female (70.8%) fish between 11 and 20 cm TL and male fish (70.5%) between 11 and 18 cm TL. The percentage of fish >20 cm TL was larger for females (30.4%) compared to males (17.6%). Total weight (TW) for female and male grey gurnard in the stratified subsample ranged from 1.9 to 499.9 g for females and 2.1–390.0 g for males, with the majority of female (66.3%) and male (76.1%) fish between 10 and 60 g. TL/TW relations for male and female fish and both sexes combined were: TW = 0.006TL³.⁰⁷, TW = 0.007TL³.⁰³ and TW = 0.007TL³.⁰⁵ respectively. Age structure (based on otolith reading) ranged between 0.5 and 7.5 years old for females and 0.5 to 5.5 years old for male with the majority of female (41.7%) and male (46.0%) fish aged as 1.5 years old. The age structure of female and male grey gurnards was significantly different with the majority of older fish (>2.5 years) being female. The von Bertalanffy growth functions were calculated as Lₜ = 32.4[1 − e⁻⁰.²⁴⁽ᵗ ⁺ ¹.⁴¹⁾] for males, Lₜ = 45.9[1 − e⁻⁰.¹⁶⁽ᵗ ⁺ ¹.³⁷⁾] for females and Lₜ = 44.0[1 − e⁻⁰.¹⁸⁽ᵗ ⁺ ¹.²⁰⁾] for both sexes combined. Instantaneous rates of total mortality were similar for males and females and the combined Z value 1.00 year⁻¹ with the natural mortality rate estimated as 0.33 year⁻¹. The size at 50% maturity (L₅₀) was estimated to be 25.3 cm TL for males, females and for both sexes combined. Age at 50% maturity (A₅₀) was 3.2 years for both males and females. The results of this study provide the first information on the population biology of E. gurnardus in the Irish Sea, the first detailed study in the NE Atlantic since 1985 and helps to address the data gap identified by ICES in knowledge of the population biology of this species.

Estimating efficiency of survey and commercial trawl gears from comparisons of catch-ratios

AbstractAssumptions about gear efficiency and catchability influence estimates of abundance, mortality, reference points and catch potential. Despite the need to better quantify fishing effects on some target species and on many non-target species taken as bycatch, there are few gear efficiency estimates for some of the most widely deployed towed fishing gears in the northeast Atlantic. Here, we develop a method that applies generalised additive models to catch-at-length data from trawl surveys and a commercial catch and discard monitoring program in the North Sea to estimate catch-ratios. We then rescale these catch-ratios and fit relationships to estimate gear efficiency. When catches of individuals by species were too low to enable species-specific estimates, gear efficiency was estimated for species-groups. Gear efficiency (and associated uncertainty) at length was ultimately estimated for 75 species, seven species-groups and for up to six types of trawl gear per species or species-group. Results are illustrated for dab (Limanda limanda), grey gurnard (Eutrigula gurnardus) and thornback ray (Raja clavata), two common non-target species and a depleted elasmobranch. All estimates of gear efficiency and uncertainty, by length, species, species-group and gear, are made available in a supplementary data file.

Feeding strategy and ontogenetic changes in diet of gurnards (Teleostea: Scorpaeniformes: Triglidae) from the Adriatic Sea

A multi-specific approach in fish diet studies provides insight into the complexity of trophic interactions in marine communities. The feeding habits of three gurnard species, Aspitrigla cuculus, Chelidonichthys lucerna and Eutrigla gurnardus (Scorpaeniformes: Triglidae), from the north-middle Adriatic Sea were studied to evaluate prey-resource partitioning amongst species and within species, comparing juveniles’ and adults’ diet for each gurnard species. A total of 1818 specimens (390 A. cuculus, 973 C. lucerna, 455 E. gurnardus) were collected by bottom trawling and they were assigned to size classes (juveniles or adults) on the basis of macroscopic evaluation of the gonads. Stomach contents were analysed. A common dietary preference for Crustacea was found in all species and size classes considered. Nevertheless, gurnards showed distinct feeding behaviour: C. lucerna and E. gurnardus were generalist-opportunistic predators, showing a varied diet based on epi-benthic, bentho-pelagic and necto-benthic preys belonging to different taxa such as Teleostei and Mollusca, while A. cuculus may be considered a specialist feeder, feeding almost exclusively on necto-benthic invertebrates. Morisita’s index calculated for critical size classes (juveniles and adults) pointed out differences. At the inter-specific level, possible dietary competition between A. cuculus and E. gurnardus (C > 0.65) was found for all size classes combined, due to the prey abundance of Lophogaster typicus (Crustacea: Mysida). At the intra-specific level, high diet overlap was found between juveniles and adults of C. cuculus (C = 0.98) and between juveniles and adults of E. gurnardus (C > 0.84). In contrast, C. lucerna did not compete with increasing body size (C < 0.20), showing a clear change from crustaceans to fish in its diet preferences. The possibility that A. cuculus and E. gurnardus may compete for the same prey resources while C. lucerna shows food resource partitioning is discussed. Better understanding of the ecology of these coexisting predators should lead to improved conservation and improved fisheries management.

PROTEIN AND PCR-RFLP ELECTROPHORESES FOR THE DIFFERENTIATION BETWEEN SOME SPECIES OF THE SEA ROBINS (PISCES, FAMILY: TRIGLIDAE)

Triglidae is a family of benthic marine fishes known as gurnards and sea robins, and are distributed throughout all the tropical and temperate seas. Electrophoresis of PCR-RFLP and SDS-proteins were used for differentiation between three gurnards and to detect their genetic relationship. Twenty four fish samples of the grey, the red and the piper gurnards were taken as eight samples from each species. Protein bands varied from 10 to 13 bands in the studied fishes, i.e. 13 bands in the grey gurnard and 10 bands in each of the piper and the red gurnards. The red gurnard recorded the highest similarity to the piper gurnard, while the red gurnard recorded lower similarity to the grey gurnard. Two primers were used for PCR amplification of 360 bp long fragments of the mt DNA cytochrome b (Cyt b) gene and 655 bp of the mt DNA cytochrome oxidase subunit I (COI) gene. The PCR products were digested by two different restriction enzymes DdeI and HincII. Digestion by these enzymes produced highly polymorphic restriction profiles. This enables the differentiation of these fishes and showed that there is a wide intraspecific COI and Cyt b genes. The phylogenetic tree based on the sharing protein bands and PCR-RFLP fragments gave similar results and revealed the relationship between the studied gurnards.

Occurrence and distribution of parasites in relation to food components of grey gurnard, Eutrigla gurnardus (L.) (Teleostei: Scorpaeniformes), off the Shetland Islands

Abstract The research was conducted on the parasite fauna and food composition of Eutrigla gurnardus caught as by-catch in commercial catches of the Atlantic cod Gadus morhua near the Shetland Islands. Thirteen species and two genera of pathogens were identified, including six species and one genus recorded for the first time in this host. Copepoda — Euphausiacea dominated in the stomach contents (they are also the intermediate hosts for most of the parasites found), while Gadidae dominated among the fish. A checklist of E. gurnardus parasites is included.

The role of silvery pout (Gadiculus argenteus) as forage prey in the Galician and Cantabrian Sea ecosystem (NE Atlantic) in the last two decades

Silvery pout (Gadiculus argenteus, Guichenot, 1850) is a very common and quite abundant species in Galicia and in the Cantabrian Sea, which plays an important role in the Cantabrian Sea ecosystem since it is one of the main trophic resources of many commercial species. In this study we analysed data obtained from a series of bottom trawl surveys carried out annually in autumn from 1990 to 2010 along the continental shelf of Galicia and the Cantabrian Sea. We examined the changes observed in the distribution patterns and abundance indices of this species and relate these with the occurrence and abundance of other commercial species in the area like hake (Merluccius merluccius), megrims (Lepidorhombus spp.) and blue whiting (Micromesistius poutassou). A significant correlation was found (R=0.45, p=0.038) between the abundance index of G. argenteus and hake, one of its main predator. A total of 137,780 stomachs of 19 most important predators were analysed during this period. The volume percentage (% V) of G. argenteus in the diet of some species was very high as it was the case of Lepidopus caudatus (94%) or Molva macrophthalma (58.2%). The frequency of occurrence (% FO) was important for these and other commercial species such as Lepidorhombus whiffiagonis (12.3%), Zeus faber (11.1%), Helicolenus dactylopterus (9.5%), Eutrigla gurnardus (8.6%), Lophius budegassa (8.9%) and M. merluccius (6.4%). There were evidences of density dependant feeding on G. argenteus. A significant correlation between G. argenteus yearly abundance in the stomachs of the assemblage of its 19 predators and survey abundance was observed (R=0.8977, p<0.01). Also, high correlation has been observed between the yearly survey biomass indices of G. argenteus and its % FO in the stomachs of hake, megrims and blue whiting for some length ranges of these predators. G. argenteus is an extremely important species in Galicia and Cantabrian Sea due to both its abundance in the ecosystem and its trophic role as forage species.

A survey of wild marine fish identifies a potential origin of an outbreak of viral haemorrhagic septicaemia in wrasse, Labridae, used as cleaner fish on marine Atlantic salmon, Salmo salar L., farms.

Viral haemorrhagic septicaemia virus (VHSV) was isolated from five species of wrasse (Labridae) used as biological controls for parasitic sea lice predominantly, Lepeophtheirus salmonis (Krøyer, 1837), on marine Atlantic salmon, Salmo salar L., farms in Shetland. As part of the epidemiological investigation, 1400 wild marine fish were caught and screened in pools of 10 for VHSV using virus isolation. Eleven pools (8%) were confirmed VHSV positive from: grey gurnard, Eutrigla gurnardus L.; Atlantic herring, Clupea harengus L.; Norway pout, Trisopterus esmarkii (Nilsson); plaice, Pleuronectes platessa L.; sprat, Sprattus sprattus L. and whiting, Merlangius merlangus L. The isolation of VHSV from grey gurnard is the first documented report in this species. Nucleic acid sequencing of the partial nucleocapsid (N) and glycoprotein (G) genes was carried out for viral characterization. Sequence analysis confirmed that all wild isolates were genotype III the same as the wrasse and there was a close genetic similarity between the isolates from wild fish and wrasse on the farms. Infection from these local wild marine fish is the most likely source of VHSV isolated from wrasse on the fish farms.

Intra-specific and inter-specific variability of the sulcus acusticus of sagittal otoliths in two gurnard species (Scorpaeniformes, Triglidae)

Morphology, morphometries and compounds of sulcus acusticus of sagittal otoliths of two gurnard species (Aspitrigla cuculus and Eutrigla gurnardus) from north-central Adriatic Sea (north-eastern Mediterranean) were investigated. The study objectives were to find morphometric variables and shape variability of sulcus acusticus of these two closely related sound producers species linked to developmental changes from juvenile to adult stage and species-specific pattern which influenced ecomorphological adaptations of the auditory system. The method used was a combination of multivariate techniques, X-ray diffractions pattern and ultrastructural investigation by SEM. Multivariate analysis (PCA, LDA and PERMANOVA) performed on standardized morphometrics of a total of 202 individuals, significantly separated four groups: A. cuculus juveniles, A. cuculus adults, E. gurnardus juveniles and E. gurnardus adults due to different life history characteristics. At intra-specific levels higher mean values of sulcus area/otoltih area (S:O) ratio of adults than the juveniles were observed within A. cuculus and not for E. gurnardus. At inter-specific levels significant differences were seen between adults and not between juvenile groups. Considering all the groups, the main variability on sulcus area were observed for caudal part of the sensorial macula. Although no differences in compounds were shown by X-ray diffraction at intra-specific level, the crystals on sulcus acusticus were different in shape, size and arrangement between juveniles and adults of each gurnard. The crystals of juveniles were quite enmeshed into otolith matrix and showed a rod/smooth-shape. The crystalline arrangement of adults became more complex with larger, rod/rectangular-shape and well-formed faces. Ontogenetic and specie-specific differences might be related to specie-specific physiological factor (i.e sexual maturity), depth distribution and feeding patterns that change during gurnards growth. These changes, relating to both endogenous and exogenous factors, were marked by the sulcus acusticus which provided a useful tool for fish ontogenetic, physiological and ecological studies.