Age determination of the Antarctic fishes Champsocephalus gunnari and Notothenia rossii marmorata from South Georgia

Summary Investigations were performed on otoliths from Champsocephalus gunnari and Notothenia rossii marmorata as part of an effort to study the population dynamics of Antarctic fishes. Examination of otoliths by scanning electron microscope (SEM) revealed internal microincrements which were similar to daily increments described for other fish species. No easily identifiable annuli could be discerned and fishes were aged by counting microincrements. Multiple regression analyses relating age to otolith morphometrics and fish size, provided a simpler ageing method. It was determined with these techniques that C. gunnari grew to 50 cm in 15 yrs and N. rossii marmorata grew to 50 cm in 6.5 yrs. The lack of larger-sized individuals for N. rossii marmorata may be indicative of recent overfishing with only the younger age groups remaining. It appears that length-at-age data determined on a yearly basis, could provide valuable scientific and management information for these species.     

Fish of Admiralty Bay (King George Island,South Shetland Islands,Antarctica)

Summary The species composition of the ichthyofauna of Admiralty Bay, King George Island was determined from results of sampling using bottom trawls, gill-nets and long-lines. Thirty-five species from 24 genera and 10 families (Table 1) were found. The number of species increased with depth (e.g. 7 species at 100 m, 14 species at 255 m and 21 species at 540 m), a tendency characteristic of Antarctic waters. In the bay, the catch rate obtained with a bottom trawl (greater than 30 kg/h) was roughly ten times lower than the catch rate using the same gear on the shelf around the Island. Notothenia gibberifrons was the dominant species in all trawls. The majority of these fish (about 95%) were immature juveniles (Table 4). Younger fish were found to inhabit shallower waters (Fig. 1). The majority of the fish of species Notothenia coriiceps neglecta, Notothenia rossii marmorata, Notothenia nudifrons, Trematomus newnesi and Trematomus bernacchii preferred waters about 255 m deep. Fourteen specimens of a previously undescribed species of the genus Psilodraco (currently being described by H. DeWitt) were caught in the bay within the 146 to 540 m depth range. The rare zoarcid, Lycenchelys aratrirostris, was also caught in Admirality Bay; previously this species had only been reported from the Elephant Island region. In the case of Trematomus newnesi, the occurrence of scales in the interorbital space was noted (Fig. 2), an observation which verifies this feature as a distinct taxonomical criterion for this species.     

Karyotypes of two Antarctic fishes,Notothenia gibberifrons andNotothenia coriiceps neglecta

The chromosomes of two species of Antarctic fishes,Notothenia (Gobionotothen) gibberifrons andNotothenia (Notothenia) coriiceps neglecta, were prepared by the air-drying method at the Polish Antarctic Station “Henryk Arctowski” during the austral summer 1984–1985. ForN. (G.) gibberifrons the diploid number is2n = 46 consisting of 2 metacentric (m) pairs, 1 submetacentric (sm) pair and 20 telocentric (t) or subtelocentric (st) pairs. ForN. (N.) coriiceps neglecta the diploid number is 2n = 22 consisting of 9 m pairs, 1 sm pair and 1st pair. Some aspects of karyological evolution of these fishes are discussed.     

The surface structure of Antarctic fish eggs and its use in identifying fish eggs from the Southern Ocean

Summary The surface structure of eggs of Notothenia neglecta, Nototheniops larseni, Nototheniops nudifrons (Nototheniidae), Champsocephalus gunnari and Chaenocephalus aceratus (Channichthyidae), collected near Elephant Island (Atlantic sector of the Southern Ocean) and of Notothenia rossii rossii (Nototheniidae) from Kerguelen waters (Indian sector of the Southern Ocean) was studied by scanning electron microscopy (SEM). Eggs of N. larseni differed from the other species by containing a micropyle with two micropyle pits. External morphological characteristics of the egg envelope such as the ultrastructure of the zona radiata, its interpore distances and the diameter of the micropyle were species-specific and could aid in the identification of fish eggs collected from the Southern Ocean.     

Bacterial flora of newly caught Antarctic fish Notothenia neglecta

Summary The heterotrophic bacterial flora of Antarctic fish Notothenia neglecta was studied in Potter Cove (King George Island, South Shetland Islands). Quantitative and qualitative analysis of aerobic bacteria from sea water, skin, stomach and intestine were carried out. In addition, anaerobic flora of stomach and intestine was studied and compared. Pseudomonas was dominant in sea water samples but, neither skin nor digestive tract samples showed to be rich in this genus. Stomach flora showed variable results between samples. The gut flora was composed almost exclusively of Vibrio. Despite extreme environmental conditions this Antarctic fish show an intestinal indigenous microflora very similar to warmer waters fish. Several factors, that we discussed, could be determining the Vibrio dominance in the gut of marine teleosts.     

Feeding plasticity of Trematomus newnesi (Pisces, Nototheniidae) in Terra Nova Bay, Ross Sea, in relation to environmental conditions

Forty-three and 49 specimens of the Antarctic fish Trematomus newnesi were collected in the coastal waters of Terra Nova Bay, Ross Sea, during December 1994 and February 1998, respectively. The dietary composition of the two fish samples was determined by means of stomach content analysis and then compared. In general, as reported in most of the previous studies, planktivory appeared to be the main feeding habit of T. newnesi. However, the different environmental conditions occurring in the study area in the two periods investigated, such as the degree of the sea-ice coverage and the related amount of light available below the ice, influenced the food composition of T. newnesi. In December 1994, the whole area investigated was covered by a thick layer of sea ice and the diet of T. newnesi consisted of few prey taxa. Some species that characterize the so-called “cryopelagic habitat”, such as the euphausiid Euphausia crystallorophias and the copepod Metridia gerlachei, were by far the most important prey, followed by amphipods and the pteropod Limacina helicina. Conversely, the ostracod Alacia belgicae and larval stages of fish (Pleuragramma antarcticum) were consumed occasionally. In late summer (February 1998), the lack of sea-ice coverage and changes in the associated fauna influenced the feeding habit of T. newnesi. In this period the food spectrum appeared to be more diverse, revealing an active feeding search in the water column. The bulk of food was composed of several prey groups, such as E. crystallorophias, hyperiid amphipods (Hyperiella dilatata), copepods, L. helicina and several species of fish larvae. Present data provide evidence of a marked feeding plasticity of T. newnesi, in response to diverse environmental conditions that characterize the High-Antarctic Zone. Accepted: 17 July 1999     

Triacylglycerol lipase activities in tissues of Antarctic fishes

. The activity of the lipolytic enzyme, triacylglycerol lipase (TAG lipase; E.C. 3.1.1.3) was measured in heart ventricle, liver, oxidative skeletal muscle, and adipose tissue of four species of Antarctic fishes (Chaenocephalus aceratus, Notothenia coriiceps, Trematomus newnesi, Gobionotothen gibberifrons). Estimates of weight-specific activities at 0°C in tissues of the Antarctic fishes were broadly comparable to those reported for temperate-zone fish species assayed at their physiological temperature. Within each species, liver tissue displayed the highest weight-specific activity of TAG lipase in C. aceratus, T. newnesi, and G. gibberifrons, while adipose tissue of N. coriiceps showed the highest activity within that species. Combining these estimates with carefully measured somatic indices of the tissues, permitted assessment of the relative importance of different tissues to overall lipolytic capacity on an organismal level. On this basis, liver tissue displays the greatest capacity of TAG lipase per 100 g body weight in each of the species studied.     

Winter aspects of the ichthyoplankton community in Antarctic Peninsula waters

Summary Ichthyoplankton was sampled from the Antarctic Peninsula area of the South Polar Ocean in early winter (May and June 1986). A total of 153 eggs from two species and 1368 larvae or juvenile stages from 12 species were obtained. These included pelagic species, and demersal species with a long pelagic larval or juvenile phase. Most abundant were larvae of Pleuragramma antarcticum and Notothenia kempi, and eggs of Notothenia neglecta. The distribution of notothenioid and paralepidid larvae was apparently unaffected by ice cover, whereas myctophid larvae were confined to ice-free waters. Areas where newly hatched Chionodraco hamatus occurred coincided with dense aggregations of Euphausia superba (Krill) furcilia larvae which is a potential food resource during winter. The hatching of icefish larvae during winter is apparently independent of the seasonal production cycle. Epipelagic eggs of Notothenia neglecta were found during the spawning season, which suggests that eggs ascend to the surface after demersal spawning and that development takes place near the sea surface during winter. Larvae of Notothenia kempi were chiefly confined to shelf and slope waters to the west of the Antarctic Peninsula, with larger larvae found in coastal shelf areas. Pleuragramma antarcticum occurred in the coastal waters off the Biscoe Islands, in the Gerlache Strait, and in the northern Bransfield Strait. The smallest larvae were found in the northern Bransfield Strait, whereas those at the Biscoe Islands and in Gerlache Strait waters were larger and of a similar size. A cyclonic gyre to the west of the Antarctic Peninsula observed in the austral summer was likely to have affected the larval drift of Pleuragramma antarcticum and Notothenia kempi. Differences in the timing of spawning and hatching and the vertical distribution of these larvae will lead to different transport and spatial distribution patterns. It is hypothesized that early winter conditions do not imply severe limitations on the year-class success of larval fish. Dispersal and increased mortality may occur during the second half of the winter.     

Dietary overlap among early juvenile stages in an Antarctic notothenioid fish assemblage at Potter Cove,South Shetland Islands

To date, studies of food overlap in Antarctic fish have been performed on a mixture of late juvenile and adult stages, leaving the young immature specimens (TL ≤ 10 cm) practically unexplored. We studied diet overlap and potential competition among early juvenile individuals in a coastal notothenioid community at Potter Cove, by analysing the stomach contents of 225 fish of 5 species collected in the summer of 2009–2010. We used frequency of occurrence (F %) and the coefficient “Q” for diet evaluation and the method of Tyler and the similarity index “S” for food overlap. Amphipods of the suborder Gammaridea were the main (Q > 2.900) and most frequent (% F) prey for all species, although Notothenia coriiceps also consumed gastropods of the family Littorinidae, mostly Laevilitorina antarctica. Secondary prey were algae for Notothenia rossii and N. coriiceps, calanoid (pelagic) and harpacticoid (benthic) copepods for Trematomus newnesi and the latter copepods and isopods of the family Munnidae for Lepidonotothen nudifrons. The reoccurrence of prey among fish species was 39.6 % and food overlap between 90 % of species pairs was under 58 %. Because similarly low values of diet overlap were reported for intermediate/advanced juveniles and adults of the same species at the same site, we conclude that there is no difference in the degree of interspecific food overlap and therefore potential competition between the immature and mature fraction of the fish community. Food competition is avoided by resource partitioning along a depth gradient or by different prey species.     

Haemogregarina nototheniae n. sp., from the blood of Antarctic nototheniids

A new species of haemogregarina, Haemogregarina nototheniae, is described from the Southern ocean teleosts Notothenia neglecta and Notothenia rossii. Stages identified as macro- and microschizogony and gametogony are described in mononuclear leukocytes from fish caught during the austral summer. The mature gametocyte is the most commonly found stage: it is exoerythrocytic, but carries the host erythrocyte nucleus attached to its external surface near one end. The gametocyte has a central nucleus and 2–16 subterminal eosinophilic granules, but no polar cap. During microschizogony the schizont nucleus undergoes repeated division without cytoplasmic division to give 32 nuclear masses, all of which appear to be in metaphase. Cytoplasmic division yields free merozoites identifiable by the coarse chromatin of the nuclear area. During macroschizogony the intraleukocytic parasite swells to a subspherical mass with a median band of fine heterochromatin granules. The cytoplasm later divides, forming three merozoites. There appear to be two routes by which merozoites proceed to become gametocytes: in winter small merozoites are seen in mature erythrocytes; but in summer, in erythroblasts. The invertebrate definitive host and the means of transmission are unknown, but the parasite is provisionally assigned to the genus Haemogregarina.     

Gametogenesis and reproductive strategies in some species of the Antarctic fish genus Trematomus (Nototheniidae) from Terra Nova Bay, Ross Sea

Species of the genus Trematomus are the most common nototheniids in the High-Antarctic Zone, and several live sympatrically on the Ross Sea continental shelf. Histological analysis of gonadal development of T. bernacchii, T. hansoni and T. newnesi was carried out on samples collected during the austral summer in the coastal waters of Terra Nova Bay, western Ross Sea. Gonads of both females and males of the three species were described based on macroscopic and histologic scales. Histologically, both males and females of T. bernacchii were in postspawning or in early maturing condition, thus indicating that they recently completed spawning. Conversely, most specimens of T. hansoni were in spawning condition, as evidenced by the histological appearance of gonads and by the high value of gonado-somatic index (GSI) of females between 20 and 36%. In the same period, females of T. newnesi had maturing ovaries, whereas males were at an early developmental stage of maturity. In all species, the testicular structure closely resembled the unrestricted spermatogonial type, although spermatogonia were more concentrated in the blind end of tubules. On the basis of the pattern of oocyte maturity observed within the ovarian lamellae, all Trematomus had a group synchronous ovary, as commonly reported in Antarctic fish. Furthermore, the presence of oocytes showing the commencement of yolk deposition in spent females confirms that vitellogenesis is a slow process, extending over at least 1 year. The reproductive strategies of Trematomus are discussed in terms of timing of the spawning season of each species as a function of the seasonal production cycle and of the interspecific relationships. The spawning activities of the three species investigated appeared to be mismatched with respect to time as well as location within the range of distribution of each.     

Electrophoretic analysis of Antarctic fish from South Georgia

White muscle samples of Antarctic fish (Notothenia rossii, N. neglecta, N. gibberifrons and Chaenocephalus aceratus) were subjected to electrophoretic tests. Isoelectric focusing of general muscle proteins provides a quick method of identifying species. Six muscle enzymes were resolved by horizontal starch gel electrophoresis. These are presumed to be the products of ten independent gene loci. Coefficients of genetic distance were calculated and substantially agree with the conventional taxonomy. Levels of genetic variability are within the normal range for marine teleosts. Two polymorphic enzymes. GPI and PGM, might prove useful as 'genetic tags' for stock identification.     

The diet of the South Georgia shag Phalacrocorax georgianus at South Orkney Islands in five consecutive years

The diet of the South Georgia shag Phalacrocorax georgianus at Laurie Island, South Orkney Islands, was studied by the analysis of 420 pellets (regurgitated casts) collected from the 1995 to 1999 breeding seasons. Demersal-benthic fish were by far the main prey, followed by molluscs (mainly octopods and bivalves) and polychaetes. Harpagifer antarcticus (in 1995, 1998, 1999) and Lepidonotothen nudifrons (1996, 1997) were the most frequent prey, followed by Gobionotothen gibberifrons or Trematomus newnesi. Harpagifer antarcticus, followed by L. nudifrons or T. newnesi, was the most numerous prey in all of the seasons and predominated in mass in 1995 and 1996, followed by Notothenia coriiceps and L. nudifrons. In 1997 and 1999, G. gibberifrons and N. coriiceps were the species that most contributed to the diet whereas N. coriiceps and H. antarcticus contributed most in 1998. Our results differ from those reported for the South Orkney Islands in previous studies. These differences could be due to the use of different diet-analysis methods and to shags-related and/or fisheries-related changes in the food availability around the colonies. These alternative explanations are analysed and discussed.     

Electrophoretic analysis of Antarctic fish from South Georgia

White muscle samples of Antarctic fish ( Notothenia rossii, N., neglecta. N. gibbe-rifrons and Chaenocephalus (aceratus ) were subjected to electrophoretic tests. lsoelectric focusing of general muscle proteins provides a quick method of iden-tyfying species. Six muscle enzymes were resolved by horizontal starch gel clectrophoresis. These are presumed to be the products of ten independent gene loci. Coefficients of genetic distance were calculated and substantially agree with the conventional taxnomy. Levels of genetic variability are within the normal range for marine teleosts. Two polymorphic enzymes. GPI and PGM. might prove useful as 'genetic tags' for stock identification.     

Larval fish distribution and abundance in the Antarctic Peninsula region and adjacent waters

The spatial distribution, species composition and abundance of ichthyoplankton in the Bransfield Strait and adjacent waters were studied during two cruises in the Antarctic spring 1991/92 and summer 1992/93 seasons. A multiple plankton net (Bioness) and a Bongo net were used to collect samples at 35 stations in 1991/92 and 75 stations in 1992/93. Early larval stages (14 species) and juveniles (13 species) representing the known Bransfield Strait ichthyofauna were present in the water column. The nototheniids predominated in the entire study area. The greatest species diversity was found in the uppermost 200 m of the water column in the Bransfield Strait. Notothenia gibberifrons and Nototheniops larseni dominated in spring, whilst in summer Pleuragramma antarcticum dominated in association with N. larseni. The dominant species in the Gerlache Strait were P. antarcticum and Notothenia kempi, while P. antarcticum and Trematomus scotti were predominant in the Bellingshausen Sea area.     

The role of the rock cod Notothenia coriiceps Richardson, 1844 in the life-cycle of Antarctic parasites

Fifty specimens of Notothenia coriiceps caught in Potter Cove, King George Island, were examined for ecto- and endoparasites. Of the 22 parasite species found, 18 were helminths, 2 were hirudineans and 2 were crustaceans. The isopod Aega antarctica and an unidentified hirudinean are reported for the first time from this fish host. Dominant parasites were the adults of Aspersentis megarhynchus, the invasive stage of Corynosoma spp. (cystacanth) and the adults of Macvicaria pennelli, with respective prevalences of infestation of 94, 76 and 74%. The preferred sites of infestation were the pylorus and intestine, where five different larval (nematodes and cestodes) and eight adult (digeneans and acanthocephalans) parasite species were found. No adult nematodes and cestodes were found and no parasites could be isolated from the musculature. The results of the present study are related to previous findings on the parasite fauna of N. coriiceps. The comparison implies a high parasite diversity in this benthic Antarctic fish species. Most parasites found appear to have a wide range of distribution within Antarctic waters together with a low host specificity. Besides its role as final host for several species of trematodes and acanthocephalans, N. coriiceps serves as transmitter of parasite larvae to piscivorous birds and seals. It is concluded that the parasite fauna in Antarctic fish species provides important insights into the different habitat use and trophic relationship of their fish hosts. Received: 11 September 1997 / Accepted: 12 January 1998     

Qualitative and quantitative analysis of serum immunoglobulins of four Antarctic fish species

Immunoglobulins from the Antarctic fish species Trematomus bernacchii, Trematomus hansoni, Trematomus newnesi, and Chionodraco hamatus were analysed in whole serum and after purification by affinity chromatography on protein A-sepharose. Using SDS-PAGE, the apparent masses of the heavy and light chains were, respectively, 83.5 kDa and 27.5 kDa for T. bernacchii, 83.5 kDa and 27 kDa for T. hansoni, 81 kDa and 27.5 kDa for T. newnesi, and 74.5 kDa and 30 kDa for C. hamatus. It was not possible to purify immunoglobulins from T. newnesi due to their low concentration in serum. Heterogeneity in mass of both heavy and light chains was observed in all species. By using a polyclonal antibody raised against sea bass immunoglobulins, cross-reactivity was observed with heavy and light chains of all species. With this antibody, an indirect enzyme-linked immunosorbent assay (ELISA) was developed and results showed the relative immunoglobulin concentration in sera of the Antarctic fish species considered, using as standard sea bass immunoglobulins. Received: 25 November 1996 / Accepted: 3 February 1997     

Annual trend of fish assemblages associated with FADs in the southern Tyrrhenian Sea

A study on fish assemblage associated with fish aggregating devices (FADs) in Sicily was carried out between January 2000 and January 2001. With a fortnightly periodicity, 156 experimental hauls were carried out by means of a purse seine in a FAD‐containing marine section banned to commercial fishing. A total of 14 229 fish specimens belonging to six families and 10 species was found. These species were Balistes carolinensis, Caranx crysos, Naucrates ductor, Seriola dumerili, Seriola fasciata, Tachurus picturatus, Coryphaena hippurus, Schedophilus ovalis, Thunnus thynnus, Polyprion americanus and showed all young‐of‐the‐year undergoing a rapid growth. The applied ordination technique highlighted the existence of four assemblage periods describing the annual trend. The results confirm that fish assemblages associated with FADs are related to season, following a fish colonization tied to natural recruitment. Comparison of the ecological indices across the four periods showed that the assemblages in the periods from summer to winter were more structured than those in spring. The quantity of individuals also showed a strong variation peaking in the summer period. The results of this study reveal that FADs represent a particular nursery area for the associated species that could influence their survival.     

Cytogenetic mapping of immunoglobulin heavy chain genes in Antarctic fish

The chromosomal location of the IgH locus has been analyzed in several bony fish of the Antarctic perciform group Notothenioidei. Two IgH probes were prepared from the species Trematomus bernacchii (family Nototheniidae, tribe Trematominae) and mapped onto the chromosomes of ten species belonging to the same genus (Trematomus) and in two outgroups, through one-color and two-color FISH. A single location of the IgH locus was found in the majority of the species examined, including the outgroups, whereas in four of them the IgH genes splited to two chromosomal loci. RT-PCR experiments revealed the presence of three allelic sequences in T. newnesi, a species in which the IgH genes were organized in two chromosomal loci. Possible pathways leading to IgH genes duplication during the diversification of trematomine fishes were inferred from the analysis of the FISH patterns in a phylogenetic context. The present work provides the first comprehensive picture of IgH genes organization at chromosomal level in a bony fish group.     

Morphology and diet are decoupled in nearshore notothenoids from King George Island,West Antarctica

Antarctic notothenioid fishes show wide adaptive morphological radiation, linked to habitat preferences and food composition. However, direct comparisons of phenotypic variability and feeding habits are still lacking, particularly in stages inhabiting nearshore areas. To assess these relationships, we collected juveniles and adults of the most common benthic species inhabiting shallow waters off the South Shetland Islands within a similar size range, the plunderfish Harpagifer antarcticus, the black rockcod Notothenia coriiceps, and the marbled rockcod Notothenia rossii. Individual size ranges varied from 44.0 to 98.9 mm standard length (LS) (H. antarcticus), from 95.8 to 109.3 mm LS (N. coriiceps), and from 63.0 to 113.0 mm LS (N. rossii). Notothenioid fish showed different morphospace variability, being larger for H. antarcticus than the other Notothenia species and associated with the position of the posterior end of the operculum, along with the location and relative size of the eye. The evolutionary allometry was low, but the static allometry was much higher, especially for H. antarcticus and N. rossii. The diet was mainly carnivorous, consisting of amphipods and euphausiids. Macroalgae were scarce or totally absent in the gut contents of all species. Only H. antarcticus showed an increase in the prey number and ingested prey volume with fish size. Finally, there was a significant covariation between shape changes and LS in all species (allometric effects), however, not with prey composition, probably due to the small size range or ontogenetic stage and the relative similarity (or lack of contrast) in the benthic environment that they utilized.