Species Of Icefishes Research Articles

Thermal profiles reveal stark contrasts in properties of biological membranes from heart among Antarctic notothenioid fishes which vary in expression of hemoglobin and myoglobin

Antarctic notothenioids are noted for extreme stenothermy, yet underpinnings of their thermal limits are not fully understood. We hypothesized that properties of ventricular membranes could explain previously observed differences among notothenioids in temperature onset of cardiac arrhythmias and persistent asystole. Microsomes were prepared using ventricles from six species of notothenioids, including four species from the hemoglobin-less (Hb-) family Channichthyidae (icefishes), which also differentially express cardiac myoglobin (Mb), and two species from the (Hb+) Nototheniidae. We determined membrane fluidity and structural integrity by quantifying fluorescence depolarization of 1,6-diphenyl-1,3,5-hexatriene (DPH) and leakage of 5(6)-carboxyfluorescein, respectively, over a temperature range from ambient (0°C) to 20°C. Compositions of membrane phospholipids and cholesterol contents were also quantified. Membranes from all four species of icefishes exhibited greater fluidity than membranes from the red-blooded species N. coriiceps. Thermal sensitivity of fluidity did not vary among species. The greatest thermal sensitivity to leakage occurred between 0 and 5°C for all species, while membranes from the icefish, Chaenocephalus aceratus (Hb-/Mb-) displayed leakage that was nearly 1.5-fold greater than leakage in N. coriiceps (Hb+/Mb+). Contents of phosphatidylethanolamine (PE) were approximately 1.5-fold greater in icefishes than in red-blooded fishes, and phospholipids had a higher degree of unsaturation in icefishes than in Hb+notothenioids. Cholesterol contents were lowest in Champsocephalus gunnari (Hb-/Mb-) and highest in the two Hb+/Mb+species, G. gibberifrons and N. coriiceps. Our results reveal marked differences in membrane properties and indicate a breach in membrane fluidity and structural integrity at a lower temperature in icefishes than in red-blooded notothenioids.

Mitochondrial membranes in cardiac muscle from Antarctic notothenioid fishes vary in phospholipid composition and membrane fluidity.

Antarctic notothenioid fishes are highly stenothermal, yet their tolerance for warming is species-dependent. Because a body of literature points to the loss of cardiac function as underlying thermal limits in ectothermic animals, we investigated potential relationships among properties of ventricular mitochondrial membranes in notothenioids with known differences in both cardiac mitochondrial metabolism and organismal thermal tolerance. Fluidity of mitochondrial membranes was quantified by fluorescence depolarization for the white-blooded Chaenocephalus aceratus and the red-blooded Notothenia coriiceps. In these same membranes, lipid compositions and products of lipid peroxidation, the latter of which can disrupt membrane order, were analyzed in both species and in a second icefish, Pseudochaenichthys georgianus. Mitochondrial membranes from C. aceratus were significantly more fluid than those of the more thermotolerant species N. coriiceps (P < .0001). Consistent with this, ratios of total phosphatidylethanolamine (PE) to total phosphatidylcholine (PC) were lower in membranes from both species of icefishes, compared to those of N. coriiceps (P < .05). However, membranes of N. coriiceps displayed a greater unsaturation index (P < .0001). No differences among species were found in membrane products of lipid peroxidation. With rising temperatures, greater contents of PC in mitochondrial membranes from ventricles of icefishes are likely to promote membrane hyperfluidization at a lower temperature than for cardiac mitochondrial membranes from the red-blooded notothenioid. We propose that physical and chemical properties of the mitochondrial membranes may contribute to some of the observed differences in thermal sensitivity of physiological function among these species.

PO2 Profiles in the Retina of the Hemoglobin‐less Icefishes

The retina of vertebrates has one of the highest O2 demands and requires a constant O2 supply. Four general types of retinal circulations have been described for O2 delivery in extant vertebrates: 1) sole reliance on the choriocapillaris; 2) capillaries penetrating the retina; 3) capillarization of the inner side of the retina; and 4) O2 secretion. Oxygen secretion is based on acid secretion into the blood resulting in a potent unloading of O2 from so‐called Root effect hemoglobins (Hb), which is augmented by venous to arterial O2 diffusion in a vascular rete lining the back side of the retina. This choroid rete mirabile (CRM) allows O2 delivery at super‐atmospheric pressure in the avascular retina of some fishes that have the thickest retinae and some of the largest eyes (relative to body size) of all extant vertebrates. The suborder Notothenioidei, which consists of Antarctic and sub‐Antarctic fishes, provides a model system to unravel how the interactions between Hb function and retinal vascularity evolved to produce modern fish eyes. While several phyletically basal notothenioids have been shown to display similar ocular arrangements as in other Perciform species containing a CRM, more phyletically derived notothenioids have highly reduced CRM or have lost it completely. Of particular interest are the species of the family Channichthyidae, icefishes, that are unique among adult vertebrates in possessing pale white blood containing only few vestigial immature erythrocytes and no Hb. Without Hb, O2 secretion is not functional, and icefishes have been demonstrated to possess heavily increased pre‐retinal capillarization most probably to maintain retinal oxygenation and preserve large eyes and thick retinae. However, whether available O2 at different retinal levels actually follows the degree of vascularization has not been tested.Using thin O2 sensors, we measured profiles of partial pressure of O2 (PO2) in the retina of six species of icefishes, two species of related, but red‐blooded dragonfishes (Bathydraconidae), and four species of more distantly related notothens (Nototheniidae). Arterial PO2 was statistically significantly higher in icefishes than in notothens [t‐test; p = 0.0066 (n = 3); PaO2 = 16.64 ± 3.84 kPa in Chaenocephalus aceratus; PaO2 = 4.42 ± 1.40 kPa in Notothenia coriiceps]. In general, pre‐retinal PO2 was high in icefishes (19.20 ± 6.35 kPa in C. aceratus), approaching the theoretical O2 solubility limit without O2 secretion. The PO2 level decreased towards the outer portion of the retina, but with a small peak on the choroid side of the retina, possibly due to a vestigial choriocapillaris. In notothens displaying Root effect, pre‐retinal PO2 was slightly lower (12.07 ± 5.12 kPa in N. coriiceps) but increased to a super‐atmospheric level on the outer portion of the retina (52.25 ± 32.46 kPa in N. coriiceps).Our results demonstrate that retinal PO2 is dictated by vascularization in the Hb‐deprived icefishes, leading to a unique reversal in the retinal oxygen profile.Support or Funding InformationUS National Science Foundation grant PLR‐1444167Carlsberg FoundationVelux FoundationsThis abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Energetic costs of protein synthesis do not differ between red- and white-blooded Antarctic notothenioid fishes

Antarctic icefishes (Family Channichthyidae) within the suborder Notothenioidei lack the oxygen-binding protein hemoglobin (Hb), and six of the 16 species of icefishes lack myoglobin (Mb) in heart ventricle. As iron-centered proteins, Hb and Mb can promote the formation of reactive oxygen species (ROS) that damage biological macromolecules. Consistent with this, our previous studies have shown that icefishes have lower levels of oxidized proteins and lipids in oxidative muscle compared to red-blooded notothenioids. Because oxidized proteins are usually degraded by the 20S proteasome and must be resynthesized, we hypothesized that rates of protein synthesis would be lower in icefishes compared to red-blooded notothenioids, thereby reducing the energetic costs of protein synthesis and conferring a benefit to the loss of Hb and Mb. Rates of protein synthesis were quantified in hearts, and the fraction of oxygen consumption devoted to protein synthesis was measured in isolated hepatocytes and cardiomyocytes of notothenioids differing in the expression of Hb and cardiac Mb. Neither rates of protein synthesis nor the energetic costs of protein synthesis differed among species, suggesting that red-blooded species do not degrade and replace oxidatively modified proteins at a higher rate compared to icefishes but rather, persist with higher levels of oxidized proteins.

Maturity and fecundity of Champsocephalus gunnari, Chaenocephalus aceratus and Pseudochaenichthys georgianus in South Georgia and Shag Rocks Islands

The reproductive biology of three species of icefishes (family Channicthyidae), Champsocephalus gunnari, Pseudochaenichthys georgianus and Chaenocephalus aceratus in South Georgia and Shag Rocks Islands was studied by means of a histological analysis. Parental care, a widespread behaviour among icefishes such as C. aceratus, is not observed in C. gunnari, which has a broadcast spawning strategy. There were large differences in total fecundity mainly due to the different sizes reached by each species (total fecundity range was 2,500–21,300 hydrated oocytes). Nevertheless, when comparing relative fecundity values, the average results were, in general, similar for P. georgianus and C. aceratus (6–9 hydrated oocytes per female gram). However, relative fecundity estimated for C. gunnari was 10–37 hydrated oocytes per ovary-free female gram. The difference may be a consequence of the smaller oocyte size of the species as compared to other icefishes. The small diameter of hydrated oocytes was also associated with low values of dry weight. The high relative fecundity recorded for C. gunnnari may compensate, in part, for a broadcast spawning strategy.

Weight-length relationships of 14 species of icefishes (Salangidae) endemic to East Asia

Summary Length-weight relationships (LWRs) of 14 species from 17 populations of salangids, which cover most species in the family Salangidae, were analyzed from 12 regions in China and Japan. A total of 952 specimens were used to estimate the relationship parameters. The allometric factor b values varied from 2.56 in Salanx cuvieri to 3.53 in Neosalanx oligodontis. Additionally, the condition factor a value was calculated setting b = 3 in the remaining six species. Nine maximum-size records and 17 LWRs of salangids are established for the first time, which will fill in some of the empty spaces on rare neotenic species in the Fishbase.

Evolution of the myoglobin gene in Antarctic Icefishes (Channichthyidae)

Antarctic icefishes (Family: Channichthyidae) are the only adult vertebrate animals that do not express the circulatory oxygen-binding protein, hemoglobin. Six species of icefishes, including Dacodraco hunteri, also do not express myoglobin (Mb), an oxygen-binding protein found in ventricular tissue of Antarctic notothenioids. Sequence of the Mb gene from D. hunteri contains a duplicated TATA box in the promoter region of the Mb gene that is absent in Chionodraco rastrospinosus, an icefish species known to express Mb. The 15-base pair insertion in D. hunteri is identical to the duplicated TATA box that is thought to be directly responsible for preventing transcription of the Mb gene in C. aceratus, another icefish species that lacks Mb expression. Sequencing of the Mb promoter from the remaining channichthyid species revealed the duplicated TATA box in 14 of 16 icefish species, including 8 species known to express Mb. Based on the presence of the duplicated TATA box in promoters of both Mb-expressing and Mb-lacking species, loss of Mb expression in D. hunteri and C. aceratus is either independent of the duplicated TATA box, or the duplicated TATA box requires presence or absence of a distant regulatory element to prevent transcription.

Freezing avoidance of the Antarctic icefishes (Channichthyidae) across thermal gradients in the Southern Ocean

Biogeographic studies separate the Antarctic Notothenioid fish fauna into high- and low-latitude species. Past studies indicate that some species found in the high-latitude freezing waters of the High-Antarctic Zone have low-serum hysteresis freezing points, while other species restricted to the low-latitude seasonal pack ice zone have higher serum hysteresis freezing points above the freezing point of seawater (−1.9°C), but the relationship has not been systematically investigated. Freeze avoidance was quantified in 11 species of Antarctic icefishes by determining the hysteresis freezing points of their blood serum, in addition, the freezing point depression from serum osmolytes, the antifreeze activity from serum antifreeze glycoproteins (AFGPs), and the antifreeze activity from serum antifreeze potentiating protein were measured for each species. Serum hysteresis freezing point, a proxy for organismal freeze avoidance, decreased as species were distributed at increasing latitude (linear regression r 2 0.66, slope −0.046°C °latitude−1), which appeared largely independent of phylogenetic influences. Greater freeze avoidance at high latitudes was largely a result of higher levels of antifreeze activity from serum AFGPs relative to those in species inhabiting the low-latitude waters. The icefish fauna could be separated into a circum High-Antarctic Group of eight species that maintained serum hysteresis freezing points below −1.9°C even when sampled from less severe habitats. The remaining three species with low-latitude ranges restricted to the waters of the northern part of the west Antarctic Peninsula and Scotia Arc Islands had serum hysteresis freezing points at or above −1.9°C due to significantly lower combined activity from all of their serum antifreeze proteins than found in the High-Antarctic Zone icefish.

Dynamics of Icefish (Salangidae) Stocks in Nanyi Lake, Eastern China: Degradation and Overfishing

ABSTRACT There are two genera and four species of icefishes in Nanyi Lake, which have been commercially exploited in the past two decades. As result, icefish yield decreased over the years, from the peak of 260 metric tons to 15 metric tons, and this change was highly correlated (t =—3.95, df = 1, p = 0.001) with increased fishing effort. Meanwhile, the size composition of the icefish assemblage dramatically changed, with significantly increased relative abundance of the small icefish category (from 0.06 to 0.91). Furthermore, sampling during the 2001 fishing season was characterized by a progressive decrease in CPUE (by 3.14 times) and an increase in relative abundance (from 0.83 to 0.97) of the smallest icefish, giving direct evidence of the stocks decline and size diminution of icefishes in relation to the commercial fishing effort. Both the historical records and the 2001 seasonal changes of the icefish stocks indicated that this resource in Nanyi Lake has been overfished and illustrated that small fishes can also be overfished to degradation when they are commercially exploited.

Two species of antarctic icefishes (genus Champsocephalus) share a common genetic lesion leading to the loss of myoglobin expression

Species of the suborder Notothenioidei dominate the fish fauna of coastal Antarctic waters. Members of one notothenioid family, Channichthyidae (Antarctic icefishes), are unique among all vertebrates in lacking the circulating oxygen-binding protein hemoglobin. Icefish species also do not uniformly express the intracellular oxygen-binding protein myoglobin (Mb) in their oxidative muscles. Our laboratory previously characterized the pattern of cardiac Mb expression in 13 of the 16 known icefish species. In this paper, we complete the survey of cardiac Mb expression among all 16 known species of icefishes. Using PAGE and immunoblot analyses, we demonstrate that both Channichthys rhinoceratus and Cryodraco atkinsoni express Mb in heart ventricle, while Champsocephalus esox does not express the protein. We report Mb gene sequences from Channichthys rhinoceratus and Champsocephalus esox genomic DNA. The Mb gene of C. esox contains the identical 5-bp duplication/insertion to that observed in congeneric Champsocephalus gunnari, a species that also does not produce Mb. This duplication in exon 2 of the Champsocephalus spp. gene causes a shift in reading frame at a position normally encoding for amino acid 91 and also results in a premature stop codon, thus disrupting translation of the normal protein. Thus, 6 of the 16 known icefish species do not express cardiac Mb. These results confirm earlier conclusions that losses of Mb expression have occurred via at least four independent events during the evolution of the icefish family. Extreme similarity of Mb genes in Champsocephalus congeners further suggests recent speciation despite early divergence of this group from the lineage leading to more derived icefishes.

Diet of two icefish species from the South Shetland Islands and Elephant Island, Champsocephalus gunnari and Chaenocephalus aceratus

The summer diet of two species of icefishes (Channichthyidae) from the South Shetland Islands and Elephant Island, Champsocephalus gunnari and Chaenocephalus aceratus, was investigated from 2001 to 2003. Champsocephalus gunnari fed almost exclusively on krill (Euphausia superba) in all years. The importance of other taxa (Themisto gaudichaudii, mysids, myctophids) in the diet was negligible. The average feeding rate of Champsocephalus gunnari inferred from an exponential gastric evacuation model was between 1.0 and 1.5% body weight per day. Most of the stomachs of Chaenocephalus aceratus were empty. Stomachs with food contained mainly krill, mysids and fish. Among the fish taken, locally abundant species formed the bulk of the diet: Gobionotothen gibberifrons in 2001, Lepidonotothen larseni and Champsocephalus gunnari in 2002 and L. larseni in 2003. An ontogenetic shift in feeding preference of Chaenocephalus aceratus was observed: fish smaller than 30 cm fed on krill and mysids, while larger animals relied primarily on fish.

Biodiversity of Chinese Icefishes (Salangidae) and their conserving strategies

Icefishes (Salangidae) originated in the Chinese Yellow Sea, and are distributed in eastern Asia. Fifteen out of the 17 global icefish species live in China's coastal area, outflow rivers and estuaries, among which six are endemic to China. The endemic icefishes include Neosalanx oligodontis, N. taihuensis, N. pseudotaihuensis, N. tangkahkeii, Hemisalanx brachyrostralis, and Salanx cuvieri. Among all the rivers that flow into the South China Sea, East Sea and Yellow Sea, the Yangtze River has been the most important one for this family, where 10 species live, including five species of freshwater icefishes. Icefishes have been appreciated as a highly nutritious food, and therefore have been a major economic resource in the Yangtze River basin. Icefishes have a wide range of food choices among species, but are very sensitive to their environments,and they develop quickly, with short life cycles, with discrete generations, high fecundity, and wide population fluctuations, and therefore, they are typical r strategy species. However, due to habitat destruction (wetland reclamation), and fragmentation (dyking), over fishing, and environmental pollution, icefish biodiversity have been declining, and some species have even become vulnerable to extinction. Meanwhile, in the past decade, a few species have been widely introduced into large lakes and reservoirs in China, and have caused problems in the recipient freshwater ecosystem. Based on reviewing the current understanding of their biology, ecology and biodiversity, we present strategies for icefish conservation, and call for an evaluation of the current threats to their biodiversity, as well as of the ecological consequences of icefish introduction, and for strengthening of basic studies on ecology and biodiversity conservation of icefish.

Concentrations of myoglobin and myoglobin mRNA in heart ventricles from Antarctic fishes.

We used a combined immunochemical and molecular approach to ascertain the presence and concentrations of both the intracellular oxygen-binding hemoprotein myoglobin (Mb) and its messenger RNA (mRNA) in 13 of 15 known species of Antarctic channichthyid icefishes. Mb protein is present in the hearts of eight species of icefishes: Chionodraco rastrospinosus, Chionodraco hamatus, Chionodraco myersi, Chaenodraco wilsoni, Pseudochaenichthys georgianus, Cryodraco antarcticus, Chionobathyscus dewitti and Neopagetopsis ionah. Five icefish species lack detectable Mb protein: Chaenocephalus aceratus, Pagetopsis macropterus, Pagetopsis maculatus, Champsocephalus gunnari and Dacodraco hunteri. Mb concentrations range from 0.44+/-0.02 to 0.71+/-0.08 mg Mb g(-)(1 )wet mass in heart ventricle of species expressing the protein. A Mb-mRNA-specific cDNA probe was used to quantify mRNA in five Mb-expressing icefishes. Mb mRNA was found in low but detectable amounts in Champsocephalus gunnari, one of the species lacking detectable Mb. Mb mRNA concentrations in heart ventricle from Mb-expressing species ranged from 0.78+/-0.02 to 16.22+/-2.17 pg Mb mRNA microg(-)(1 )total RNA). Mb protein and Mb mRNA are absent from the oxidative skeletal muscle of all icefishes. Steady-state concentrations of Mb protein do not parallel steady-state concentrations of Mb mRNA within and among icefishes, indicating that the concentration of Mb protein is not determined by the size of its mRNA pool.

Topography of unpaired fins with respect to the vertebrae and similarities among icefishes of the family Channichthyidae

Overall similarities among all genera and 18 of 20 species of icefishes, family Channichthyidae, were determined based on data of the composition of axial metameric structures (unpaired fins and vertebral column). The results of a cluster analysis are compared with some traditional ideas and the cladistic phylogenetic hypothesis about the interrelationships of icefishes.

Taxonomy, biology and abundance of icefishes, or noodlefishes (Salangidae), in the Yellow River estuary of the Bohai Sea, China

Four species of icefishes were sampled in the Yellow River estuary of the Bohai Sea from April 1984 to April 1985 and from February 1988 to June 1989. Morphological analysis showed that they belonged to three subfamilies of Salangidae: one species from Protosalangicae, Protosalanx chinensis; two species from Salanginae, Salanx ariakensis and Salanx prognathus; and one species, Neosalanx andersoni, from Salangichthyinae, a new subfamily. External morphological characteristics, population composition, growth, maturity, food habits, longevity, fecundity, abundance and distribution of these icefishes are described. Based on these analyses, a clear outline of taxonomy, zoogeography aod biology of icefishes in the Yellow River estuary of the Bohai Sea was established.

Taxonomy, biology and abundance of icefishes, or noodlefishes (Salangidae), in the Yellow River estuary of the Bohai Sea, China

Four species of icefishes were sampled in the Yellow River estuary of the Bohai Sea from April 1984 to April 1985 and from February 1988 to June 1989. Morphological analysis showed that they belonged to three subfamilies of Salangidae: one species from Protosalangicae, Protosalanx chinensis; two species from Salanginae, Salanx ariakensis and Salanx prognathus; and one species, Neosalanx andersoni, from Salangichthyinae, a new subfamily. External morphological characteristics, population composition, growth, maturity, food habits, longevity, fecundity, abundance and distribution of these icefishes are described. Based on these analyses, a clear outline of taxonomy, zoogeography aod biology of icefishes in the Yellow River estuary of the Bohai Sea was established.

Features of gametogenesis and sexual cycles of six notothenioid fishes from East Antarctica

Some features of gametogenesis and sexual cycles of three species of the genus Trematomus (fam. Nototheniidae)-Trematomus centronotus Regan, T. eulepidotus Regan and T. scotti (Boulenger) and three species of icefishes (fam. Channichthyidae)-Chionodraco hamatus (Lonnberg), Ch. myersi Tyler and Neopagetopsis ionah Nybelin-were studied at Davis and Mawson Seas during austral autumn (March–April), 1983. Two peculiarities of the sexual cycles of Trematomus species may be noted: the uniform state of gonads of mature specimens of each species, and differences in time of spawning (austral summer and autumn for T. centronotus and T. eulepidotus, and, evidently, beginning of spring or the end of winter for T. scotti). Among the features of gametogenesis of icefishes are the early accumulation of yolk in oocytes, and the beginning of polarization and homogenization of yolk in oocytes, which are far from definitive sizes. Some differences in spawning time were registered in first maturing and repeatedly maturing specimens of Ch. hamatus. Repeatedly maturing specimens probably begin to spawn in December–January; those maturing for the first time evidently still spawn in March–April. Ch. myersi and N. ionah, judging by singular mature specimens, supposedly spawn during austral autumn.