Fish Caught Off Research Articles

Population connectivity in a highly migratory fish, Japanese Spanish mackerel (Scomberomorus niphonius), along the Chinese coast, implications from otolith chemistry

Connectivity is a vital component of metapopulation and fishery ecology, influencing fundamental processes such as population dynamics, evolution, and community responses to climate change. The Japanese Spanish mackerel, Scomberomorus niphonius, is an economically important species in the temperate and subtropical waters of the Northwestern Pacific Ocean, especially in the China seas. As a highly migratory species, the population connectivity of S. niphonius is not only limited to dispersal in the pelagic larval stage but throughout the whole life history, and then determines the natal origin and population structure. However, knowledge about population connectivity is scarce and, at present, is no formal management strategy to ensure the long-term sustainability of the S. niphonius fishery in China. In this study, otolith chemistry was applied to investigate the connectivity among four spawning grounds along a latitudinal gradient spanning much of the known species range in the Yellow Sea and the East China Sea [Qingdao (QD), Lvsi (LS), Xiangshan (XS) and Fuzhou (FZ)]. Otoliths from age-1 spawning or spent individuals were analyzed from the core to the margin by using laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). In each sampled life stage, otolith elements are similar among fish from different spawning grounds, but otolith chemical compositions vary greatly between life stages. Decreasing Ba:Ca ratio indicates ontogenetic migrations from relatively shallow coastal water during larval growth to relatively deep offshore waters with increasing age. The random forest classification and non-metric multi-dimensional scaling show a strong overlap in otolith elemental composition. The hereby results indicate a large-scale connectivity in the life history of S. niphonius: the immature fish mix to a large extent when they feed and overwinter in the extensive offshore waters; adults spawned in the same spawning ground have multiple natal origins and fish caught off QD may even be of FZ origin. Clustering of near core chemistry pointed to three sources, with southern grounds dominated by a single cluster while northern grounds dominated by two or three clusters. From these results, it was suggested that the local mackerel assemblages on which fisheries rely in the Yellow Sea are collectively influenced by the recruitment of all the spawning assemblages along China coastal waters instead of self-sustaining.

High mercury concentrations in Atlantic Goliath Grouper: Spatial analysis of a vulnerable species

The Atlantic Goliath Grouper Epinephelus itajara is currently a protected species in the southeastern United States waters of the Atlantic and the Gulf of Mexico and is considered vulnerable throughout its geographic range. In this study, I evaluated mercury concentrations in their tissues (muscle, liver), which revealed high concentrations (μg/g ww) of mercury (mean ± SE) in liver (6.18 ± 0.86) and muscle (1.12 ± 0.06) tissue that increased with size and age. Mercury concentrations were highest in fish caught off Florida's Atlantic coast, but varied on a finer regional scale. Mercury concentrations in muscle tissue were generally greater near urbanized areas with known mercury sources and environmental conditions appropriate for higher methylation rates. This suggests that management should consider improving the water quality in these areas to reduce the risk of health effects to human consumers and to the fish themselves.

Prevalence of anisakid parasites in fish collected from Apulia region (Italy) and quantification of nematode larvae in flesh

Anisakis spp. and Hysterothylacium spp. are nematodes that commonly parasitize several fish species. Nematode larvae can be recovered in coelomic cavity and viscera, but also in flesh and have an important economic and public health impact. A total of 1144 subjects of wild teleosts, 340 samples of cephalopods and 128 specimens of farmed fish collected from Apulia region were analysed for anisakid larvae detection by visual inspection of coelomic cavity and viscera and by digestion of the flesh. No nematode larvae were found in farmed fish and cephalopod molluscs. All examined wild-caught fish species were parasitized, except for 5 species for each of which only a few subjects belonging to the same batch were sampled, therefore the results are just indicative. A total of 6153 larvae were isolated; among these, 271 larvae were found in the muscular portion. Larvae were identified by morphological method as belonging to the genera Anisakis (97.2%) (type I and type II) and Hysterothylacium (2.8%). Both nematodes could be found in all fish species, except for round sardinella (Sardinella aurita), infected only by Hysterothylacium spp. and for Mediterranean scaldfish (Arnoglossus laterna), little tunny (Euthynnus alleteratus) and chub mackerel (Scomber japonicus) infected only with Anisakis spp.. A sample of 185 larvae was sent to the National Reference Centre for Anisakiasis (C.Re.N.A.) of Sicily for identification at the species level: 180 larvae belonged to the species A. pegreffii and 2 larvae to A. physeteris. The remaining 3 larvae were identified at genus level as Hysterothylacium. Statistical indices such as prevalence, mean intensity and mean abundance were calculated. Chub mackerel (S. japonicus) was the species with the highest prevalence and mean intensity. Moreover, the average and the median values of larvae per 100 g of edible part for each fish species were determined to estimate the consumer exposure to Anisakis spp.. The obtained values were then recalculated by referring to the edible part of all specimens (infected and non-infected) forming a single parasitized batch, getting more realistic and objective data useful for risk assessment. Our results indicate that the consumption of raw or undercooked wild fish caught off Apulian coasts could result in the acquisition of anisakiasis; on the contrary, farmed fish and cephalopods appear to be safer for the consumer.

Caligus lini n.sp., a new caligid (Copepoda, Siphonostomatoida) parasitic on the brilliant pomfret Eumegistus illustris Jordan & Jordan (Perciformes, Bramidae) of Taiwan.

Caligus lini n.sp., a new species of caligid copepod parasitic on the gill rakers and caudal fin of the brilliant pomfret, Eumegistus illustris Jordan & Jordan (Perciformes, Bramidae), is described from fish caught off Tai-Dong, Taiwan. The new species differs from its congeners by its possession of the following, unique combination of features: (1) middle two elements at the tip of leg 1 simple (without accessory process), (2) innermost element shortest and smallest of the four terminal elements on leg 1, (3) leg 4 exopod with an armature formula of I,III, and (4) complex leg 5 represented by 2 seta-bearing processes, a simple anterior process tipped with 1 plumose seta and quadripartite posterior process carrying 3 setae (1 simple and 2 plumose). The new species differs from its closest congener, Caligus tylosuri (Rangnekar, 1956), in the structure of the middle two elements (simple without carrying accessory process) at the tip of leg 1 and a quadripartite (instead of tripartite) posterior process on leg 5.

ASSESSING MULTIREGIONAL ECONOMIC IMPACTS OF ALASKAN FISHERIES: A COMPUTABLE GENERAL EQUILIBRIUM ANALYSIS

Alaskan industries, including the seafood industry, are characterized by strong linkages with the rest of the United States, including a large leakage of factor income to, and large imports of goods and services from the rest of the US, especially the West Coast region. This study develops a multiregional computable general equilibrium (MRCGE) model of three US economic regions: Alaska (AK), the West Coast (WC), and the rest of the US (RUS). The model is applied to issues affecting Alaskan fisheries, and is used to calculate the multiregional economic effects, including spread effects, of changes in: (i) the volume of fish caught off AK; (ii) the demand for Alaskan seafood by both the US and the rest of the world; and (iii) currency exchange rates.

Huffmanela hamo sp. n. (Nematoda: Trichosomoididae: Huffmanelinae) from the dagger-tooth pike conger Muraenesox cinereus off Japan.

Huffmanela hamo sp. n. is described from eggs only, which were found in black spots in the somatic musculature of a dagger-tooth pike conger, Muraenesox cinereus (Forsskål), caught off Japan. The eggs are 66-77 microm (mean 72 microm) in length and 33-38 microm (mean 35 microm) in width. The surface of the eggs is smooth and bears neither envelope nor filaments. The species is distinguished from other members of the genus by the dimensions of its eggs and the characteristics of their surface. This is the first species of Huffmanela Moravec, 1987 to be described from an anguilliform fish, and the twentieth nominal species in the genus. Similar black spots with eggs were reported four times in ten years from this fish caught off Japan; although eggs could not be examined, it is likely that the same species was involved in all cases.

Molecular and epidemiological data on Anisakis spp. (Nematoda: Anisakidae) in commercial fish caught off northern Sardinia (western Mediterranean Sea)

Anisakiasis is a fish-borne zoonosis caused by third stage larvae of the nematode Anisakis sp. present in fish or cephalopods. This is the first contribution to the molecular identification and epidemiology of Anisakis spp. in commercial fish from the Gulf of Asinara (Sardinia, western Mediterranean Sea). Between April 2006 to November 2011, 777 specimens of 10 fish species (Engraulis encrasicolus, Merluccius merluccius, Micromesistius poutassou, Phycis blennoides, Sardina pilchardus, Sardinella aurita, Scomber colias, Sphyraena viridensis, Trachurus mediterraneus, Trachurus trachurus) were examined for Anisakis sp. larvae. A total of 1286 larvae were found in 218 fish. The great majority of larvae were located in the body cavity, and only a small part (60, 4.7%) in the muscle. All the Type I larvae (1272) were identified as Anisakis pegreffii and all the Type II (14) as Anisakis physeteris, confirming that A. pegreffii is the dominant species and the most important agent of human anisakiasis in the western Mediterranean Sea.

Presence of Anisakid Larvae in the European Anchovy, Engraulis encrasicolus, Fished Off the Tyrrhenian Coast of Central Italy

A survey was carried out to determine the prevalence of anisakid nematode larvae in European anchovy (Engraulis encrasicolus) fished off the Tyrrhenian coast of central Italy. From February through July 2012, 1,490 specimens of E. encrasicolus caught in three different fishing areas (off Civitavecchia, Anzio, and Gaeta in the northern, central, and southern Lazio region of Italy, respectively) were tested for the presence of anisakid larvae, both by visual microscopic inspection and enzymatic digestion. In each of the three fishing areas, each of two sampling times produced 250 fish (with the exception of one sampling time in Gaeta that produced 240 fish). Larvae of the family Anisakidae were detected with an overall estimated prevalence of 2.3%, and each positive fish harbored a single larva. No anisakid larvae were detected in fish caught off Gaeta. Fish with larvae were significantly longer (standard length) than fish without larvae. Twenty-six larvae (74.3%) were detected by visual inspection of the viscera, eight larvae (22.8%) were detected by visual inspection of the fillets, and one larva (2.8%) was detected after digestion of pooled fillets. Molecular analysis to fully characterize the 35 detected larvae revealed 15 specimens of Anisakis pegreffii, 10 specimens of Hysterothylacium aduncum, and one hybrid genotype of A. pegreffii × Anisakis simplex. For nine specimens, no visible product was obtained after PCR amplification. The overall prevalence for A. pegreffii and H. aduncum was 1.0 and 0.7%, respectively. A comparison between fishes harboring A. pegreffii larvae and those harboring H. aduncum revealed that those with A. pegreffii were significantly heavier. The prevalence of anisakid larvae found in the present study is lower then that reported previously in E. encrasicolus collected in the Mediterranean Sea.

FEEDING HABITS OF THE SUEZ CANAL MIGRANT SQUIRRELFISH, SARGOCENTRON RUBRUM, IN THE MEDITERRANEAN SEA

ABSTRACT The squirrelfish, Sargocentron rubrum (Forsskal, 1775), is a successful Suez Canal immigrant common along the Mediterranean coast of Israel and caught occasionally in small quantities in commercial catch by trammel net and by hook-and-line. Monthly samples of stomach contents of this fish caught off 'Akko (Acre), Israel, from October 1979 to October 1980 were examined. Decapoda constituted the bulk of the diet, the remainder being Polychaeta, Isopoda, Mollusca and fishes. S. rubrum feeds intensively in summer and lightly in winter. Seasonal predominance of each taxon in the diet was measured by an alimentary coefficient calculated as a product of the frequency and weight percentages. Brachyura constituted 77.8% in summer, 94.7% in fall and winter; Anomura constituted 82.4% in spring. Pisidia longimana, Portunus hastatus, Xantho spp. and Pilumnus hirtellus were the most commonly-found prey. No preference for feeding on Suez Canal invertebrate immigrants of Red Sea origin was observed. It is conclu...

Evidence of hybridisation within the genus Chrysoblephus and conserved nuclear sequences of South African sparids (Teleostei: Sparidae)

Several hybridisation events have been recorded in marine fish, yet there is little information for southern African species. Here we present evidence for hybridisation within the genus Chrysoblephus (Sparidae), by analysing a fish caught off KwaZulu-Natal, off the east coast of South Africa. We utilise three mitochondrial (16S, COI and Cyt b) and four nuclear markers (1st intron of the S7 ribosomal protein gene, Tmo-4C4, Histone 3 and 18S rRNA) to resolve the hybrid parentage. MtDNA analyses support C. anglicus as the maternal lineage. Analyses of the Tmo-4C4 gene and the first intron of the S7 gene show six and four heterozygous positions for the hybrid fish respectively. The heterozygous positions are shared by C. anglicus and C. puniceus, which suggests C. puniceus to be the paternal lineage, with the hybrid being a first generation cross. Morphologically, the hybrid mostly resembles C. puniceus, with some meristic counts overlapping with other sparid species. Interestingly, only two of the four nuclear markers show variation within the sparids sampled in this study; 1 160 bp of 18S rRNA and Histone 3 were invariable even between the genera Chrysoblephus, Gymnocrotaphus, Petrus and Pachymetopon, suggesting conserved nuclear evolution or a rapid speciation within this group of endemic fishes.

Local feed fish supplies and possible offshore aquaculture in California

Key to the economic viability of offshore aquaculture in California is whether or not the revenues available after the costs of all other inputs have been covered are sufficient to cover the costs of the feed fish required. To investigate this, we calculated the break-even price of feed fish by: fixing the share of the farmed fish price representing the unit costs of the non-feed inputs; fixing the amount of feed fish needed per unit of farmed fish production; and varying the price of the farmed species. We found that the recent ex-vessel prices of five potential feed fish caught off California were below the calculated break-even price corresponding to the expected market price for candidate aquaculture species. While the California landings of these five species individually can be quite volatile, there would seem to be sufficient supplies in total to make offshore aquaculture in California economically viable.

Molecular Characterization of Anisakis Larvae from Fish Caught Off Sardinia

Anisakis spp. larvae are parasitic, and potentially zoonotic, nematodes transmitted by marine fish and cephalopods, which are the main intermediate hosts of the third larval stage. The accidental consumption of infected raw or poorly cooked fish may cause gastroenteric diseases and allergies in humans. The aim of the present study was to use polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) to define the occurrence, species variability, and host preferences of Anisakis spp. larvae in fish caught off the coast of Sardinia. Necropsy was used on 285 samples; 552 Anisakis spp. L3 larvae were isolated from 87 fish that tested positive for this nematode. Anisakis pegreffii was most frequently encountered (90.6%), with a primary preference for Scomber scombrus, Zeus faber, and Trachurus mediterraneus. In contrast, the prevalence of Anisakis physeteris was only 1.3%. A hybrid genotype of Anisakis simplex sensu stricto and Anisakis pegreffii was also observed, which confirms the results of previous studies carried out in the western Mediterranean. Interestingly, no Anisakis simplex s.s. larvae were recovered. These results indicate that the diversity of Anisakis species is low in Sardinia waters, probably because of its geographic position.

FIRST RESULTS ON THE PRESENCE AND THE MOLECULAR CHARACTERIZATION OF ANISAKID NEMATODES IN MARINE FISH CAUGHT OFF NORTHERN SARDINIA

Anisakidosis is a parasitic zoonosis caused by nematodes of the family Anisakidae, belonging to the genera Anisakis, Contracaecum and Pseudoterranova. Molecular studies have shown that Anisakis larvae comprise a number of sibling species, which have different genetic structures, hosts and geographical distribution. A great variety of fish species can harbour infectious third stage larvae of this nematode. The preliminary results of a study carried out to evaluate the occurrence of this parasite in commercial fish caught off northern Sardinia are herein reported. From October 2008 to November 2009, 599 specimens of 8 commercial fish species were examined for anisakid larvae through visual inspection of body cavity and peptic digestion of the muscle. Isolated Anisakis sp. larvae were observed at light microscope and identified as Type I or Type II (sensu Berland, 1961). Out of 599 fish examined, 239 (40%) were infected by 1187 anisakid larvae, belonging to the genera Anisakis (1169 Type I and 18 Type II) and Hysterothylacium (692). The molecular identification of Anisakis spp. was carried out on a subsample of 30% of Type I larvae and all Type II larvae. Specimens were firstly examined using a species-specific PCR, with primers designed for Anisakis pegreffii (APEF) and Anisakis physeteris (APHF), and ITS-2 of nuclear rDNA. The results were confirmed by the analysis of the ITS region of nuclear rDNA (ITS-1, 5.8S and ITS-2) using the restriction enzymes HinfI and HhaI in PCR-RFLP. Type I larvae examined were all identified as A. pegreffii, and Type II were all A. physeteris. This is the first contribution to the epidemiology and molecular characterization of Anisakis spp. in commercial fish caught off Sardinia.

Otolith chemistry indicates large-scale connectivity in Chilean jack mackerel ( Trachurus murphyi), a highly mobile species in the Southern Pacific Ocean

Chemistry in material laid down prior to capture along the edges of otoliths of Chilean jack mackerel ( Trachurus murphyi) showed strong spatial heterogeneity corresponding to hydrographic structure across putative population boundaries between (i) the western and eastern South Pacific Ocean, and (ii) Chile and Peru. Yet the chemistry of the otolith nucleus, in material laid down during early life, showed no evidence supporting the existence of these boundaries. Instead, jack mackerel from New Zealand had similar nucleus chemistry to most sampling areas off South America; and those off southern Peru showed similar nucleus chemistry to most sampling areas off Chile. Strong differences were found between southern and northern Peru, and cluster analysis indicated this was caused by a group of fish off northern Peru with chemistry found nowhere else. Most other fish grouped in two clusters, which showed properties suggesting correspondence with a major spawning zone in oceanic water off central Chile, and a smaller area in coastal water off northern Chile, characterized by similar sea surface temperature, lack of westward transport, and low kinetic energy. Rather than discrete populations separated by boundaries, these results suggest complex spatial structure defined by environmentally mediated survival and connectivity: fish caught off New Zealand may be of South American origin; the spawning zone off central Chile may supply fisheries around the South Pacific; and spawning off northern Chile may be an important source of fish caught locally and in Peru. However, northern Peru does not supply areas further south.

When to count your eggs: Is fecundity in Greenland halibut ( Reinhardtius hippoglossoides W.) down-regulated?

Fecundity in several fish species is subjected to down-regulation by atresia so if fecundity is estimated many months before spawning, this will be an overestimation of the realised fecundity (actual number of eggs spawned). In order to get accurate measurements of fecundity it is important to have knowledge on when potential fecundity (estimated fecundity at time of sampling) closely resembles the realised fecundity. Down-regulation of fecundity for Greenland halibut ( Reinhardtius hippoglossoides W.) was assessed using fish caught off East Greenland in 1998, 1999 and 2000. The fish caught in 1998 and 1999 were in early and late stages of vitellogenesis, respectively of the same maturation cycle. The fish caught in 2000 were also in an early stage of vitellogenesis. Fecundity decreased by 43% between early and late vitellogenesis. Fecundity in 1999 appeared to be the second lowest recorded for Greenland halibut but it is believed to be due to developmental stage rather than low productivity. There was no difference in fecundity between 1997 and 1998. It is believed that differences in fecundity between years only become apparent in late maturation as size during oocyte recruitment has a very large influence on fecundity. Neither Fulton's condition nor hepatosomatic index had any significant influence on fecundity.

Pseudorhabdosynochus argus n. sp. (Monogenea: Diplectanidae) from Cephalopholis argus, P. minutus n. sp. and Diplectanum nanus n. sp. from C. sonnerati and other monogeneans from Cephalopholis spp. (Perciformes: Serranidae) off Australia and New Caledonia.

Monogeneans from three species of Cephalopholis, namely C. argus, C. sonnerati and C. boenak, are described from fish caught off New Caledonia, South Pacific, with comparisons with material from off Queensland, Australia. Pseudorhabdosynochus argus n. sp. from C. argus is present off New Caledonia and Australia; it is characterised by its male quadriloculate organ with very elongate cone, and its sclerotised vagina with anterior trumpet, coiled primary canal and distal part with two chambers and an accessory part. C. boenak has no monogeneans off New Caledonia, but off Australia it harbours Pseudorhabdosynochus sp., a new species which is morphologically related to P. argus. P. minutus n. sp. from C. sonnerati is characterised by its minute body and a sclerotised vagina with two spherical chambers. Diplectanum nanus n. sp. from C. sonnerati is characterised by its very small funnel-shaped male copulatory organ and minute body. A new species, Haliotrema sp. from C. sonnerati is characterised by a very elongate tubular penis; it is distinct from H. cromileptis Young, 1968 (redescribed herein from specimens collected from Cromileptes altivelis off New Caledonia). The species described here include the first members of Pseudorhabdosynochus and the first diplectanids described from species of Cephalopholis. There is no evidence for a clade of Pseudorhabdosynochus species specific to members of Cephalopholis, since the species described here share similarities with other species from Epinephelus. However, it is suggested that the gill structure of Cephalopholis spp. imposes selection toward small body sizes for monogeneans.

Can otolith elemental signatures record the capture site of Patagonian toothfish (Dissostichus eleginoides), a fully marine fish in the Southern Ocean?

Otolith chemistry has been successfully used to reconstruct the environmental history experienced by estuarine-dependent teleost fish, including movement between estuaries and coastal areas. However, application has been more limited in species exposed exclusively to oceanic waters, where gradients in physical and chemical properties are less extreme. To test whether otolith elemental signatures record spatial information in an oceanic species, we sampled otoliths from Patagonian toothfish (Dissostichus eleginoides) and used an inductively coupled plasma mass spectrometer (ICP-MS) coupled to a laser ablation system to target the outer otolith edges corresponding to the period immediately before capture. Using multivariate analysis of variance and multivariate discriminant analysis, we found that edge signatures discriminated toothfish by geographic region with near complete success: only 5% of fish caught off South America and in the Antarctic were misclassified to sampling areas in the other region. Moreover, edge signatures showed strong differences between sampling areas within each region: fish captured off South America classified to sampling areas therein with 79%–84% success, and Antarctic fish classified to sampling areas therein with 50%–67% success. These results compare favourably with rates of classification for estuarine-dependent fish, demonstrating that otolith elemental signatures can discriminate the geographic provenance of oceanic and estuarine-dependent fish.

Petroleum hydrocarbon residues in the marine environment of Bassein–Mumbai

The paper reports PHc contamination in water, sediment and biota of the coastal area of Bassein–Mumbai in relation to relatively less polluted sites (Dabhol and Ratnagiri) off the west coast of India. To facilitate inter-comparison three standards have been used though the results are reported in terms of SAM (Residue of Saudi Arabian Mix crude). The concentration of PHc in water off Bassein–Mumbai varies widely (2.9–39.2 μg l −1) as compared to the average baseline (2.8 μg l −1) with higher values generally confined to creeks and estuaries. The higher concentration of PHc in the bottom water of shallow areas is attributed to the contribution from the sediment-associated petroleum residue. High concentration of PHc in the surficial sediment of inshore area Ratnagiri (107.7 ppm, dry wt) is perhaps the remnants of an oil spill that occurred in the Bombay High region on May 17, 1993. The majority of values of PHc concentration in the surficial sediment of the Bassein–Mumbai region exceed 15 ppm (dry wt) against the expected background (<3 ppm, dry wt) and the trend is indicative of transfer of PHc loads from the inshore areas to the open-shore sediments. The PHc concentration of 0.8–2.6 ppm (dry wt) in sediment deposited prior to the first global commercial use of petroleum in core R5 represents the biogenic background. Based on the period of industrialisation and the horizon of PHc accumulation, a sedimentation rate of 0.2 and 1.0 cm y −1 respectively is estimated for cores U11 and U12. Substantial increase in the concentration of PHc in sediment after 1950 in cores T8 and T10 correlates well with the establishment of refineries on the western shore of the Thane Creek in 1955–1960. A minor peak in most cores in the top 10 cm sediment probably results from biological transfer of PHc lower into the sediment by benthic organisms. Excess of PHc retained in the sediment of the Bassein–Mumbai region over the biogenic background is estimated at 40,000 t. The PHc residues (1.8–10.8 ppm, wet wt) in fish caught off Bassein–Mumbai do not suggest bioaccumulation.

A Study of Long-term Changes in Summer Infection Levels of Japanese Flounder Paralichthys olivaceus with the Monogenean Neoheterobothrium hirame in the Central Sea of Japan, with an Application of a New Technique for Collecting Small Parasites from the Gill Filaments.

Neoheterobothrium hirame infection of 0-year wild Japanese flounder Paralichthys olivaceus was investigated. This study was based on annual samples (preserved in formalin or alcohol) totalling 316 fish caught off Igarashi-hama in July and/or August of 1989-1993 and 505 fish caught off Murakami City in August of 1993-1999, Niigata Prefecture. A stirring method was developed to collect the monogenean from the fixed gill filaments. All the parasites were dislodged from the fixed gill filaments by stirring gills of individual hosts in 150 mL of water with a magnet (40 mm long and 8 mm in diameter) at 1150-1200 rpm for 20 min and 30 min for the 0-year fish and 1-year fish, respectively. Adult parasites were macroscopically observed on the buccal cavity wall, whereas immature ones on the gill arches and rakers were detected under a stereomicroscope. No N. hirame was found from 1989 to 1992. The earliest records were from samples caught off Igarashi-hama and Murakami City in 1993, though the prevalence of infection was very low. The parasite occurrence changed annually in the Murakami samples. The annual fluctuations may have been influenced by the infection level of co-existing 1-year fish and the population size of 0-year fish recruited each year. It is inconclusive whether or not the monogenean is an indigenous parasite of Japanese flounder in this area.

Age estimation for juvenile Notothenia rossii from Potter Cove, South Shetland Islands

Scales and whole otoliths were used for age estimation of juvenile Notothenia rossii specimens collected at Potter Cove, King George Island, South Shetland Islands, between 1983 and 1988. Results from the analysis of both types of material showed 96.7% agreement. Likewise, the examination of otolith cross sections of chosen specimens confirmed in all the cases the age readings obtained from the second whole sagittal otolith. Although the commonly accepted 1 July was used as the birth date of the fish for age calculations, data indicate that 1 October is closer to the biological birth date, since this species hatches in Spring. The length-age range of the fish was 18–44 cm and 3–7 years respectively, which fits well with the known length-age distribution of juvenile specimens of the species in the fjord. A comparison between observed and back-calculated mean length of age group 3 (24.6 and 25 cm respectively) indicated that not only the larger fish but the full size range of this age group was represented in our samples. Mean length data at age presented here are similar to the ones reported for fish from Admiralty Bay, King George Island, but differ from those of fish caught off Elephant Island. The use of whole otoliths for age estimation of juvenile N. rossii proved to be a reliable method with a precision of one year but, this might not be an appropriate technique for adult specimens.