Icefish Species Research Articles

Feeding Behaviour of Seven Icefish Species (Channichthyidae) in the Ross Sea, Antarctica

The Channichthyidae, a monophyletic fish group belonging to the suborder Notothenioidei, are uniquely adapted to the polar environment. However, while their physiology has been extensively studied, studies on their ecology are relatively rare. Here, we investigated the trophic ecology of seven icefish species (Chaenodraco wilsoni, Chionobathyscus dewitti, Chionodraco hamatus, Dacodraco hunteri, Neopagetopis ionah, Pagetodes antarcticus and Pagetopsis macropterus) by using the traditional morphometric approach to assess the relationship between form and feeding function. The suction index (SI), the mechanical advantage in jaw closing (MA) and nine morphological traits related to feeding structures have been analysed. Icefish species are characterised by non-protractible, elongate jaws and a wide gape; such morphological features influence the low values of both MA and SI, supporting their ram-feeding habit. The ecomorphological differences among species resulted mainly determined by the anatomical structures related to SI. Such differences do not seem to be determined primarily by the type of prey, as is the case in other taxonomic groups of Notothenioidei, but rather by phylogenetic proximity. A 3D animation was developed to visualise the different feeding modes of two icefish species (C. hamatus and P. macropterus) which are characterised by different approaches to prey.

Ontogenetic diet shifts and temporal separations in gonad development of two icefish species in Hongze Lake, China

Abstract Resource partitioning through temporal, spatial and/or trophic dimensions is suggested as a mechanism for long‐term coexistence among sympatric species. However, how the combined effects of the different dimensions contribute to the partitioning during the ontogenetic process is unclear. We sampled two sympatric icefish species [Protosalanx hyalocranius (Abbott, 1901) and Neosalanx taihuensis (Chen, 1956)] monthly from July 2015 to June 2016 in Hongze Lake, China. We evaluated the hypothesis that combined effects of separation in gonad development dynamics and ontogenetic diet shifts facilitate resource partitioning in temporal and trophic dimensions during the entire life cycle process of the two icefish species. Increased gonadosomatic index (GSI) of female P. hyalocranius occurred during October 2015 to January 2016, and that of female N. taihuensis occurred during January to March 2016. Thus, energy and nutrition investments in gonad development separated seasonally between the two species. Consequently, temporal separations in gonad development between P. hyalocranius (GSI peaked in January) and N. taihuensis (GSI peaked in March) indicated potential segregations in spawning time and consequent larval abundance peaks, suggesting reduced overlap of prey consumption during the early life stages. The dominant diet of P. hyalocranius shifted from cladocerans to copepods, and then shrimp, and finally to fish during its ontogeny, whereas the dominant diet of N. taihuensis changed gradually from cladocerans to copepods during its ontogeny. The diet overlap in cladocerans during May was high between the two species. Our findings support the hypothesis of an associative strategy, combining temporal (separations in gonad development and subsequently spawning time) and trophic (ontogenetic diet shifts) dimensions, for the resource partitioning between P. hyalocranius and N. taihuensis, which may be an important mechanism for long‐term coexistence among sympatric short‐lived fishes.

The Only Vertebrate with Clear Blood: The Antarctic Icefish

Today, the Channichthyidae are regarded to be one of the greatest anomalies in scientific history. As the only vertebrates to have clear blood, the Antarctic Icefish have abandoned a way of life that once supported its ancestors in the past, and one that supports animals in the present. The event that triggered this anomaly was the deletion of the β-globin subunit of the hemoglobin gene, rendering the gene to be completely obsolete. In addition to the loss of the hemoglobin gene, the myoglobin gene was also lost in all of the icefish species. Because Icefish could no longer transport oxygen through their blood, they lost their scales and adapted by diffusing oxygen into their blood plasma through their enlarged gills instead. The Icefish also have antifreeze proteins that bind to ice crystals to hinder their growth. It is in this manner that they are able to survive in the frigid waters of the Antarctic.

Life history and population structure of the Antarctic icefish, Pagetopsis maculata (Notothenioidei, Channichthyidae) from the Weddell Sea

The life history traits of many large-sized and commercial Antarctic icefishes are reasonably well known, except for smaller species such as Pagetopsis maculata Barsukov and Permitin, 1958. Therefore, we provide, for the first-time, data on growth and reproductive biology of this species based on a representative sample collected in the Weddell Sea during summer. Individual age and gonad stage of development were assessed by sagittal otolith readings and histological analysis of gonads respectively. The sampled population had an equal sex ratio and was composed of adult specimens spread over a wide size range. Both sexes exhibited isometric body growth and comparable condition factors. The estimated life span and growth parameters were similar between sexes, although females attained a larger asymptotic size than males, consistent with the length-frequency distributions. Typically, the reproductive investment of females, based on the gonadosomatic index, was larger than in males, although they both attained sexual maturity at a similar size. Most individuals were at an advanced stage of gonad maturity, indicating imminent spawning in late summer-early autumn. Compared to other icefish species with different geographical distributions, maximum sizes and lifestyles, P. maculata had the lowest growth performance and reproductive investment, primarily because of its smaller body size.

Quantitative Proteomics and Network Analysis of Differentially Expressed Proteins in Proteomes of Icefish Muscle Mitochondria Compared with Closely Related Red-Blooded Species.

Simple SummaryAntarctic icefish are unusual in that they are the only vertebrates that survive without the protein haemoglobin. One way to try and understand the biological processes that support this anomaly is to record how proteins are regulated in these animals and to compare what we find to closely related Antarctic fish that do still retain haemoglobin. The part of the cell that most clearly utilises oxygen, which is normally transported by haemoglobin, is the mitochondrion. Therefore, we chose to catalogue all the proteins and their relative quantities in the mitochondria (pl.) from two different muscle types in two species of icefish and two species of red-blooded notothenioids. We used an approach called mass spectrometry to reveal relative amounts of the proteins from the muscles of each fish. We present analysis that shows how the connections and relative quantities of proteins differ between these species.Antarctic icefish are extraordinary in their ability to thrive without haemoglobin. We wanted to understand how the mitochondrial proteome has adapted to the loss of this protein. Metabolic pathways that utilise oxygen are most likely to be rearranged in these species. Here, we have defined the mitochondrial proteomes of both the red and white muscle of two different icefish species (Champsocephalus gunnari and Chionodraco rastrospinosus) and compared these with two related red-blooded Notothenioids (Notothenia rossii, Trematomus bernacchii). Liquid Chromatography-Mass spectrometry (LC-MS/MS) was used to generate and examine the proteomic profiles of the two groups. We recorded a total of 91 differentially expressed proteins in the icefish red muscle mitochondria and 89 in the white muscle mitochondria when compared with the red-blooded related species. The icefish have a relatively higher abundance of proteins involved with Complex V of oxidative phosphorylation, RNA metabolism, and homeostasis, and fewer proteins for striated muscle contraction, haem, iron, creatine, and carbohydrate metabolism. Enrichment analyses showed that many important pathways were different in both red muscle and white muscle, including the citric acid cycle, ribosome machinery and fatty acid degradation. Life in the Antarctic waters poses extra challenges to the organisms that reside within them. Icefish have successfully inhabited this environment and we surmise that species without haemoglobin uniquely maintain their physiology. Our study highlights the mitochondrial protein pathway differences between similar fish species according to their specific tissue oxygenation idiosyncrasies.

Developmental constraint shaped genome evolution and erythrocyte loss in Antarctic fishes following paleoclimate change

In the frigid, oxygen-rich Southern Ocean (SO), Antarctic icefishes (Channichthyidae; Notothenioidei) evolved the ability to survive without producing erythrocytes and hemoglobin, the oxygen-transport system of virtually all vertebrates. Here, we integrate paleoclimate records with an extensive phylogenomic dataset of notothenioid fishes to understand the evolution of trait loss associated with climate change. In contrast to buoyancy adaptations in this clade, we find relaxed selection on the genetic regions controlling erythropoiesis evolved only after sustained cooling in the SO. This pattern is seen not only within icefishes but also occurred independently in other high-latitude notothenioids. We show that one species of the red-blooded dragonfish clade evolved a spherocytic anemia that phenocopies human patients with this disease via orthologous mutations. The genomic imprint of SO climate change is biased toward erythrocyte-associated conserved noncoding elements (CNEs) rather than to coding regions, which are largely preserved through pleiotropy. The drift in CNEs is specifically enriched near genes that are preferentially expressed late in erythropoiesis. Furthermore, we find that the hematopoietic marrow of icefish species retained proerythroblasts, which indicates that early erythroid development remains intact. Our results provide a framework for understanding the interactions between development and the genome in shaping the response of species to climate change.

Regulation of splenic contraction persists as a vestigial trait in white-blooded Antarctic fishes.

In fishes, the spleen can function as an important reservoir for red blood cells (RBCs), which, following splenic contraction, may be released into the circulation to increase haematocrit during energy-demanding activities. This trait is particularly pronounced in red-blooded Antarctic fishes in which the spleen can sequester a large proportion of RBCs during rest, thereby reducing blood viscosity, which may serve as an adaptation to life in cold environments. In one species, Pagothenia borchgrevinki, it has previously been shown that splenic contraction primarily depends on cholinergic stimulation. The aim of the present study was to investigate the regulation of splenic contraction in five other Antarctic fish species, three red-blooded notothenioids (Dissostichus mawsoni Norman, 1937, Gobionotothen gibberifrons Lönnberg, 1905, Notothenia coriiceps Richardson 1844) and two white-blooded "icefish" (Chaenocephalus aceratus Lönnberg, 1906 and Champsocephalus gunnari Lönnberg, 1905), which lack haemoglobin and RBCs, but nevertheless possess a large spleen. In all species, splenic strips constricted in response to both cholinergic (carbachol) and adrenergic (adrenaline) agonists. Surprisingly, in the two species of icefish, the spleen responded with similar sensitivity to red-blooded species, despite contraction being of little obvious benefit for releasing RBCs into the circulation. Although the icefish lineage lost functional haemoglobin before diversifying over the past 7.8-4.8 millions of years, they retain the capacity to contract the spleen, likely as a vestige inherited from their red-blooded ancestors.

Icefish Adaptations to Climate Change on the South Georgia Island Shelf (Sub-Antarctic)

Icefish populations continue to decline. Historical as well as current over-exploitations of stocks aggravated by climate change are frequently seen as responsible for the decline. However, natural oscillations in Antarctic fish and krill populations associated with natural climatic fluctuations, co-occurring with fisheries exploitation hinder determining the reasons for the population changes and the extent that long-term climate change may play in it. Based on data collected from South Shetland and South Orkney Islands (2956 fish stations) and South Georgia Island (2460 fish stations) covering a period from 1976 to 2017 we sought to relate decreases in krill and icefish populations to predator-prey interactions coupled with global warming influences. Our results show that the situation is complex and that many factors, e.g., competition between different icefish species, food choice and availability, and growth parameters, need to be considered. Pseudochaenichthys georgianus and Chaenocephalus aceratus biomasses, for example, oscillate in opposite directions and the two species differ with regard to the ranges they occupy in cold and warm water years. This reduces their competition for food, so that their combined biomasses oscillate little with thermal changes.

Infestation dynamics between parasitic Antarctic fish leeches (Piscicolidae) and their crocodile icefish hosts (Channichthyidae)

An understanding of host–parasite interactions represents an important, but often overlooked, axis for predicting how polar marine biodiversity may be impacted by continued environmental change over the next century. Here, we survey three species of crocodile icefish (Notothenioidei: Channichthyidae) collected from two island archipelagos in the southern Scotia Arc region for evidence of leech infestations. Specifically, we report on infestation prevalence, intensity, spatial patterns of relative abundances, size distribution of parasitized fish, and patterns of host and attachment site specificity. Our results reveal high levels of attachment area fidelity for each leech species. These results suggest skin thickness and density of the vascular network constrain leech attachment sites and further suggest trophic (i.e., post-cyclic) transmission to be an important axis of parasitization. We also demonstrate that, while leech species appear to be clustered spatially, this clustering does not appear to be correlated with fish biomass. This study illuminates the complex interactions among fish hosts and leech parasites in the Southern Ocean and lays the groundwork for future studies of Antarctic marine leech ecology that can aid in forecasting how host–parasite interactions may shift in the face of ongoing climate change.

A review of the Icefish species from the genus Channichthys Richardson, 1844 (Channichthyidae) with double-rowed gill rakers

The present work is dedicated to a modern complex morphological study on a representative sample (42 fish specimens from the stock collection of the Zoological Institute RAS and 3 specimens-holotypes from the collection of the Zoological Museum of the National Museum of Natural History NAS of Ukraine) Kerguelen icefish of the genus Channichthys Richardson, 1844 (Channichthyidae) with a special structure of the gill apparatus – double-rowed gill rakers: charcoal icefish Channichthys panticapaei Shandikov, 1995, big-eyed icefish Ch. bospori Shandikov, 1995, and pygmy icefish Ch. irinae Shandikov, 1995. All this species of icefish, with their common similarity, are united by the special structure of the gill apparatus - the presence of two well-developed rows of gill rakers on the gill arches, especially on the first gill arch, which is a key defining sign that is clearly distinguishes them from all other species of the genus Channichthys. Until now, there is no unambiguous universally accepted opinion of specialists about the taxonomic status of these icefish. They are distinguished either in one species, or in three species, or are identified as Channichthys sp. In the course of this work, a redescription of Ch. panticapaei with the confirmation of the validity of this species, based on complex data of external morphology, the study of the seismic sensor system and especially the structure of the gill apparatus, highlighting the most important diagnostic features of the species, as well as the replace of the species Ch. bospori and Ch. irinae, to the synonymy of Ch. panticapaei.

Characterization of complete mitochondrial genome of Pogonophryne albipinna (Perciformes: Artedidraconidae)

The complete mitochondrial genome of Pogonophryne albipinna was determined by the MiSeq platform, which was the first report in the family Artedidraconidae. The circular form of its mitochondrial genome was 17,086 bp, which contained the canonical eukaryotic 37 genes. The gene orders of P. albipinna was identical to the other icefish species, in which there was additional non-coding region and translocation of ND6 gene. Except for ATP6 gene and COI (GTG), 11 genes begin with the typical start codon, while incomplete stop codons (T– –) were identified in COII, ND4, and CytB. Phylogenetic tree with the currently known mitogenomes in suborder Notothenioidei showed that P. albipinna was located distinctly from those in Bathydraconidae and Nototheniidae forming a unique cluster as Artedidraconidae. The first complete mitochondrial genome of P. albipinna would be the fundamental data to understand the evolutional relationship of icefish species in the Antarctic Oceans.

Intergeneric hybrids inform reproductive isolating barriers in the Antarctic icefish radiation

Interspecific hybridization or barriers to hybridization may have contributed to the diversification of Antarctic icefishes (Channichthyidae), but data supporting these hypotheses is scarce. To understand the potential for hybridization and to investigate reproductive isolating mechanisms among icefish species, we performed in vitro fertilization experiments using eggs from a female blackfin icefish Chaenocephalus aceratus and sperm from a male of another genera, the ocellated icefish Chionodraco rastrospinosus. Sequencing of genomic and mitochondrial DNA confirmed the intergeneric hybrid nature of resulting embryos which successfully developed and hatched as active larvae at about four and a half months during the Antarctic winter. This result demonstrates the compatibility of gametes of these two species and the viability of resulting zygotes and larvae. Due to logistic constraints and the slow developmental rate of icefishes, we could not test for long-term hybrid viability, fertility, fitness, or hybrid breakdown. Analysis of our fishing records and available literature, however, suggests that the strongest barriers to hybridization among parapatric icefish species are likely to be behavioral and characterized by assortative mating and species-specific courtship and nesting behaviors. This conclusion suggests that, in long-lived fish species with late sexual maturity and high energetic investment in reproduction like icefishes, pre-mating barriers are energetically more efficient than post-mating barriers to prevent hybridization.

Maximum cardiac performance of Antarctic fishes that lack haemoglobin and myoglobin: exploring the effect of warming on nature’s natural knockouts

Antarctic notothenioids, some of which lack myoglobin (Mb) and/or haemoglobin (Hb), are considered extremely stenothermal, which raises conservation concerns since Polar regions are warming at unprecedented rates. Without reliable estimates of maximum cardiac output (n}{}dot{Q}), it is impossible to assess their physiological scope in response to warming seas. Therefore, we compared cardiac performance of two icefish species, Chionodraco rastrospinosus (Hb−Mb+) and Chaenocephalus aceratus (Hb−Mb−), with a related notothenioid, Notothenia coriiceps (Hb+Mb+) using an in situ perfused heart preparation. The maximum n}{}dot{Q}, heart rate (fH), maximum cardiac work (WC) and relative ventricular mass of N. coriiceps at 1°C were comparable to temperate-water teleosts, and acute warming to 4°C increased fH and WC, as expected. In contrast, icefish hearts accommodated a higher maximum stroke volume (VS) and maximum n}{}dot{Q} at 1°C, but their unusually large hearts had a lower fH and maximum afterload tolerance than N. coriiceps at 1°C. Furthermore, maximum VS, maximum n}{}dot{Q} and fH were all significantly higher for the Hb−Mb+ condition compared with the Hb−Mb− condition, a potential selective advantage when coping with environmental warming. Like N. coriiceps, both icefish species increased fH at 4°C. Acutely warming C. aceratus increased maximum n}{}dot{Q}, while C. rastrospinosus (like N. coriiceps) held at 4°C for 1 week maintained maximum n}{}dot{Q} when tested at 4°C. These experiments involving short-term warming should be followed up with long-term acclimation studies, since the maximum cardiac performance of these three Antarctic species studied seem to be tolerant of temperatures in excess of predictions associated with global warming.

Ice fish otoliths record dynamics of advancing and retreating sea ice in Antarctica

AbstractTrace element concentrations within fish otoliths act as biological tags and environmental chronometers within aquatic environments. Linking patterns in elemental concentrations within ice fish otoliths to sea ice dynamics allows us to better understand the chemical dynamics of ice‐covered environments. Here laser ablation inductively coupled plasma mass spectrometry was used to measure the concentrations of conservative and bioactive trace elements in yearly otolith bands of two benthic ice fishes and one cryopelagic ice fish collected from sites along the gradient in sea ice persistence in McMurdo Sound, Antarctica. We used a 12‐yr time series of satellite images to define summertime extent of ice cover from 2002 to 2014. Elemental concentrations of Sr and Li were higher in the otoliths of the cryopelagic species, while Mn concentrations were higher in the otoliths of benthic species, reflecting differences in species' association with sea ice melt and formation. Multivariate dispersion of individual elemental concentrations was greater within the cryopelagic species, indicative of their more transient residence among sites. Key bioactive and conservative elements differed among years with contrasting sea ice dynamics for both cryopelagic and benthic ice fish species. These differences were likely due to sea ice formation concentrating trace metals from the water column and incorporating resuspended sediments, dust, or glacial meltwater with high metal content. Our results provide strong evidence for the effectiveness of trace element concentration profiles in otoliths as environmental recorders of the dynamics of sea ice conditions, and for the role of ice fish as environmental sentinels in Antarctica.

Whole genome sequencing of Chinese clearhead icefish, Protosalanx hyalocranius.

Background: Chinese clearhead icefish, Protosalanx hyalocranius, is a representative icefish species with economic importance and special appearance. Due to its great economic value in China, the fish was introduced into Lake Dianchi and several other lakes from the Lake Taihu half a century ago. Similar to the Sinocyclocheilus cavefish, the clearhead icefish has certain cavefish-like traits, such as transparent body and nearly scaleless skin. Here, we provide the whole genome sequence of this surface-dwelling fish and generated a draft genome assembly, aiming at exploring molecular mechanisms for the biological interests. Findings: A total of 252.1 Gb of raw reads were sequenced. Subsequently, a novel draft genome assembly was generated, with the scaffold N50 reaching 1.163 Mb. The genome completeness was estimated to be 98.39 % by using the CEGMA evaluation. Finally, we annotated 19 884 protein-coding genes and observed that repeat sequences account for 24.43 % of the genome assembly. Conclusion: We report the first draft genome of the Chinese clearhead icefish. The genome assembly will provide a solid foundation for further molecular breeding and germplasm resource protection in Chinese clearhead icefish, as well as other icefishes. It is also a valuable genetic resource for revealing the molecular mechanisms for the cavefish-like characters.

Expansion of capacities for iron transport and sequestration reflects plasma volumes and heart mass among white-blooded notothenioid fishes.

The family Channichthyidae or "icefishes" (suborder Notothenioidei) represents the only vertebrates lacking hemoglobin (Hb) as adults. Several icefish species also do not express cardiac myoglobin (Mb). We address how levels of proteins involved in iron (Fe) processing (transport, sequestration, and export) vary among white- and red-blooded notothenioids, and whether absence of Hb and/or Mb in channichthyids is accompanied by expansion of contents of Fe-binding proteins to protect against unchaperoned Fe. Levels of transferrin (Tf), ferritin (Ft), ceruloplasmin (Cp), and non-heme Fe were quantified in plasma, serum, and/or nonhematopoietic tissues (cardiac ventricle, skeletal muscle, and liver) from species of white-blooded (Chaenocephalus aceratus, Champsocephalus gunnari, Chionodraco rastrospinosus, Pseudochaenichthys georgianus) (the first two species not expressing Mb) and red-blooded (Notothenia coriiceps, Gobionotothen gibberifrons) notothenioids. We also measured levels of ascorbate (Asc), a mediator of Fe uptake. While plasma concentrations of Tf and tissue levels of Asc are similar among species, concentrations of plasma Asc are lower in white-blooded species. Concentrations of Ft and non-heme Fe and activities of Cp are also generally reduced in icefishes compared with red-blooded notothenioids. The presence of cardiac Mb in some icefish species does not appear to influence levels of proteins involved in Fe processing. To address further the question of Fe sequestration within a physiological context, we account for well-characterized differences in blood volume and heart mass among white- and red-blooded notothenioids. We report that total contents of plasma Tf are greater, while ventricle non-heme Fe is at least at parity in white- vs. red-blooded species.

Total Mercury Contents of Antarctic Toothfish Dissostichus mawsoni Caught in the Antarctic Sea

Abstract Mercury is an element of special concern for human health. Measurements of total mercury levels in fish have been taken into con-sideration to assess risk. In this study, the Antarctic toothfish Dissostichus mawsoni was evaluated as a potential safe food source through measurement of total mercury contents. Total mercury concentrations in Antarctic toothfish ranged from 0.101 ± 0.047 mg/kg to 0.139 ± 0.075 mg/kg. The total mercury concentration was significantly correlated with macroscopic values including total fish length, weight, gonadosomatic index, and maturity ( P < 0.01 or 0.05). Furthermore, according to the risk assessment, the total mercury body exposure rate from Antarctic toothfish ranged from 2.125% to 2.847% of the Provisional Tolerable Weekly Intake. Therefore, the Antarctic toothfish could be used as a potential safe seafood source. Key words: Dissostichus mawsoni , Antarctic toothfish, Mercury, Risk assessment, Safe seafood source Introduction The cod icefish species internationally known as the tooth-fish can be classified into the Antarctic toothfish

Evidence for past and present hybridization in threeAntarctic icefish species provides new perspectives on an evolutionary radiation

Determining the timing, extent and underlying causes of interspecific gene exchange during or following speciation is central to understanding species' evolution. Antarctic notothenioid fish, thanks to the acquisition of antifreeze glycoproteins during Oligocene transition to polar conditions, experienced a spectacular radiation to >100 species during Late Miocene cooling events. The impact of recent glacial cycles on this group is poorly known, but alternating warming and cooling periods may have affected species' distributions, promoted ecological divergence into recurrently opening niches and/or possibly brought allopatric species into contact. Using microsatellite markers and statistical methods including Approximate Bayesian Computation, we investigated genetic differentiation, hybridization and the possible influence of the last glaciation/deglaciation events in three icefish species of the genus Chionodraco. Our results provide strong evidence of contemporary and past introgression by showing that: (i) a substantial fraction of contemporary individuals in each species has mixed ancestry, (ii) evolutionary scenarios excluding hybridization or including it only in ancient times have small or zero posterior probabilities, (iii) the data support a scenario of interspecific gene flow associated with the two most recent interglacial periods. Glacial cycles might therefore have had a profound impact on the genetic composition of Antarctic fauna, as newly available shelf areas during the warmer intervals might have favoured secondary contacts and hybridization between diversified groups. If our findings are confirmed in other notothenioids, they offer new perspectives for understanding evolutionary dynamics of Antarctic fish and suggest a need for new predictions on the effects of global warming in this group.

Interannual variability in the feeding of ice fish (Notothenioidei, Channichthyidae) in the southern Scotia Arc and the Antarctic Peninsula region (CCAMLR Subareas 48.1 and 48.2)

We have studied the annual variation in food intake of three sub-Antarctic ice fish species (Champsocephalus gunnari, Chaenocephalus aceratus, and Pseudochaenichthys georgianus) and three high-Antarctic ice fish species (Chionodraco rastrospinosus, Cryodraco antarcticus, and Chaenodraco wilsoni). Stomach content analyses were conducted during bottom trawl surveys around the South Shetland Islands in 1998, 2001, 2002, 2003, and 2007, the South Orkney Islands in 1999 and 2009, and off the north-western Antarctic Peninsula in 2002, 2006, and 2006/2007 in order to obtain further insight into the amount of food of Antarctic demersal fish consume during summer. Annual variation in food intake was comparatively low within an area in the krill-feeding species C. gunnari and C. wilsoni. Food intake was much more variable, by a factor of 2 or 3 among years and areas, in larger C. aceratus and C. antarcticus, which rely heavily on fish as their dietary source. Food consumption was intermediate in the two species P. georgianus and C. rastrospinosus, which rely on both krill and fish.

Effects of hydrologic regulation on icefish population dynamics, assemblage structure and fishery yield in Lake Nanyi, China

AbstractStock dynamics and demographic parameters of a family of annual icefishes (Salangidae) were investigated in Lake Nanyi in eastern China before and after construction of irrigation infrastructure. After hydroregulation, two of four icefish species, a migratory species (Hemisalanx brachyrostralis) and a previously rare species (Neosalanx tangkahkeii) were absent from survey samples. The relative abundance of the remained icefish stocks changed greatly. The spring and autumn stocks of N. taihuensis increased from 9.9% and 1.7% to 74.8% and 4.8%, respectively, and N. oligodontis decreased from 84.8% to 20.4%. Total icefish density (CPUE) and yield doubled under the new hydrologic regime. Average adult body size and absolute fecundity of the three persistent icefish stocks decreased, and this could have resulted from slower rates of growth and development of larvae and juveniles in response to greater density of icefishes overall and more intense competition for planktonic food resources during summer and fall.