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A photographic seabed survey conducted off the Antarctic Peninsula region provided the opportunity to study spatial patterns, abundance and behaviour of the notothenioid benthic fish fauna. Overall, a total of 12,715 images taken with the Ocean Floor Observation System (OFOS) along 26 transects in three ecoregions (Joinville Island, Bransfield Strait and Drake Passage) were analysed. The fish fauna consisted of at least 34 species belonging to four families of both low-Antarctic and high-Antarctic origin. Nototheniids showed the highest relative abundance and species richness, followed by channichthyids, bathydraconids and artedidraconids. Direct in-situ observations in OFOS seabed images allowed descriptions of fish behaviour, such as aggregation of individuals (Notothenia coriiceps), specific body postures (Cygnodraco mawsoni and Cryodraco antarcticus) and parental care (Chaenodraco wilsoni, Chionodraco rastrospinosus, Pagetopsis macropterus and Trematomus hansoni). Fish density and species richness was primarily correlated with the occurrence of bryozoans, ascidians, and large cup-shaped sponges, providing a three-dimensional habitat suitable for fish settling, foraging, breeding and refuge from predators. Fish diversity was higher (a) off Joinville Island and in Bransfield Strait than in Drake Passage, where almost exclusively low-Antarctic species were recorded, and (b) between 100 and 600 m than at greater depths. Overall, the benthic fish fauna off the northern Antarctic Peninsula is zoogeographically composite and widespread, with well-structured spatial partitioning.

The bigeye notothen, Trematomus tokarevi, is a rare nototheniid fish with a putative circum-Antarctic distribution. Due to its prevalent deep water occurrence, this species is rarely caught and its biology poorly known. In addition, this species has been often misidentified with Trematomus nicolai, a morphologically similar species with a partially overlapping distribution. The odd catch of a few specimens of T. tokarevi in the southern Weddell Sea enabled us to provide for the first time preliminary data on reproductive traits and individual age of this species. Fish sample consisted of five females, collected in the austral summer north east of the Filchner Trough at about 750 m depth. Based on histological analyses of gonads, smaller females were in early developing phase, whilst larger ones were regressing, suggesting a summer spawning season, as reported elsewhere. The analysis of growth rings pattern of sagittal otoliths allowed to estimate the individual age, which ranged between 4 and 10 years. In conclusion, this species exhibits most of the common biological traits described in other trematomids, although with some peculiarities, showing at the same time low fecundity and small egg size at spawning.

Parental care is a rather common reproductive strategy in fishes, particularly in species with low fecundity and large eggs as the Antarctic icefish (Channichthyidae). The infrequent use of underwater devices to record fish behaviour and the logistic limitations of operating in the Antarctic marine environment have prevented, so far, the collection of data about rare species. Integrating results from benthic trawling and underwater photographic images, we provide the first demographic and reproductive behavioural data for the channichthyid Neopagetopsis ionah, describing the nesting and parental care behaviour of a spawning population in the south-eastern Weddell Sea. The population sampled by the Agassiz trawl was dominated by females, and consisted of several post-spawning as well as a few mature females spread over a narrow size range. Based on otolith reading, the population included two cohorts estimated as four- and five-year-old fish. Following common trade-off between fecundity and egg size, females of N. ionah spawned few large eggs (733-1810 eggs/female, 4.9-6.5 mm in diameter). The nesting site was characterized by fine sediments with sparse gravel and the accompanying benthic invertebrate community showed low densities and was relatively poor. A total of 93 nests were counted along the video transect, most of them with a single guarding male or left unattended. Fish remains or whole dead specimens were frequently observed in the proximity of the nest. This observation represents the first record of post-spawning mortality associated with parental care which has never been documented before in Antarctic fishes.

Because sister species share a phenotypic axis, they hold morphological and ecological traits in common and, when sympatric, are ideal subjects for examining the extent of morphological divergence associated with the non-shared ecological parameters of the niche. Trematomus lepidorhinus and T. loennbergii have overlapping depth ranges of > 1000 m and occupy the deep shelf-upper slope niche in the waters of East Antarctica, an area where glacial troughs and their 1000-1500 m-deep landward basins (innershelf depressions) encompass 40% of the sea floor. The sense organ and brain divergence between the two species at the gross anatomical and histological levels involves differences in: number of olfactory lamellae, composition of the photoreceptor array and the number of retinal cells, size of the cephalic lateral line pores, and overall size of the brain and degree of development of different brain regions. Size and shape of the sagittal otoliths also differ. The morphology is unequivocally differentiating for habitat depths and conclusively documents a shift toward reliance on non-visual senses in T. loennbergii, consistent with collection data indicating this species lives at greater depths than T. lepidorhinus. Depths of peak abundances--200-500 m for T. lepidorhinus and 600-800 m for T. loennbergii--are the major differentiating parameter, with the ?300 m differential between the peaks providing considerable, although not absolute, habitat separation. This is also reflected in the greater absolute abundances of the shallower-living T. lepidorhinus in trawl catches. Only T. loennbergii is found near the floors of 1000-1500 m-deep innershelf depressions, a distinctive microhabitat on the high latitude shelf.

Despite their wide distribution around the Antarctic continent, the life strategies of the long-fingered icefish Cryodraco antarcticus have been rarely investigated and are not well understood. The aim of this paper was to provide more insights on the demographic characteristics of the population living off the South Shetland Islands, focusing attention on key biological traits such as age and growth and the reproductive cycle. Individual age and reproductive status were assessed through the microstructural analyses of sagittal otoliths and histological analysis of gonads, respectively. The sex-balanced sampled population consisted of juvenile and adult fishes covering a wide size range. Both sexes had positive allometric growth, although males exhibited smaller maximum size and lower body condition than females. Fish longevity was comparable between sexes, being 16 and 18years in males and females, respectively. Applying the von Bertalanffy growth model to length-at-age estimates, males consistently reached lower maximum asymptotic size at a faster rate than females. Based on the gametogenic process, the spawning period was inferred to occur from late summer to early autumn. As commonly found in icefishes, females devoted a great investment to reproduction as gonadosomatic index, egg size, and fecundity. A single female (62cm TL) spawned about 7730 eggs as large as 3–4mm. Considering also the results of previous studies conducted in other areas, this species is characterized by a long-lasting pelagic juvenile phase and adults share similar life strategies across the range of their spatial distribution, suggesting the possibility of a single panmictic circum-Antarctic population.

The Artedidraconidae is the most speciose of the five Antarctic notothenioid families. Bottom trawling in the Weddell Sea has yielded a new species herein described from two specimens, a juvenile and an immature female. Artedidraco longibarbatus differs from other species of Artedidraco in having a much longer mental barbel (about 25 % SL vs. 4–14 % SL). While recent genetic studies indicate that Artedidraco is paraphyletic, we choose to follow traditional taxonomy based on morphology. Selected meristic data and a key to the seven species of Artedidraco are provided.

The rock cod Patagonotothen ramsayi (Regan 1913) is the most abundant species of the genus Patagonotothen, occurring along the Patagonian shelf. It plays an important role in the demersal food web both as prey and predator, showing an increasing importance for the local finfish and squid trawl fisheries. Age structure and the reproductive traits were investigated from the population inhabiting the eastern shelf of Burdwood Bank, which represents the southernmost area of its geographical distribution. Adult specimens of P. ramsayi were collected during bottom trawling carried out in the austral summer. The specimens were aged by otolith readings, and their reproductive characteristics were assessed by macroscopical and histological analyses. Age was similar between sexes, ranging from 4 to 7 and from 4 to 8 years in males and females of comparable size, respectively. GSI was relatively low in females ( 1 mm) were found in three females. Absolute fecundity ranged from approximately 30 to 120 thousands of eggs. No relationship was found between female size and fecundity, probably due to the relatively narrow range of the investigated fish sizes. Males were in the spent (VII) or resting (II) stages.

Although it has been reported that Notothenia rossii elsewhere hatches in spring, our daily increment back-counting from the capture date in otoliths of fingerlings caught in Potter Cove, South Shetland Islands, in the 2000s, showed two main periods of larval hatching, one in summer (February–March) and another in winter (July). In concordance, the simultaneous presence of two cohorts born the same year was identified in the age/length frequency distribution of fish sampled in spring 2010, which belonged to biological ages 0+ and 1+ and hatched, respectively, in summer and winter–spring. Maximum and minimum ages of pelagic blue-phase and demersal brown-phase fingerlings were, respectively, 227 and 240 days, indicating a demersal settlement after about 8 months from hatching. The estimated growth rate was 0.23–0.33 mm/day, equivalent to that of South Georgia fingerlings and higher than those of other nototheniids of similar size range. Based on early life events associated with the hatching periods, two types of life cycles are hypothesised for South Shetland fingerlings. The pelagic blue-phase fingerlings (6.5–7.6 cm TL, age group 0+) hatched in July (winter cohort), entering in Potter Cove in February–March. The brown-phase fingerlings (6.3–10.6 cm, mostly of age group 0+) hatched in February–March (summer cohort) and were collected in the cove in spring (the smaller specimens) or in summer (the larger ones). Finally, early juveniles (10.7–15.5 cm, age group 1+) hatched in winter, mainly in July (winter cohort), entering in the cove the following year to spend the second winter inshore. Fil: Barrera Oro, Esteban. Ministerio de Relaciones Exteriores, Comercio Interno y Culto. Dirección Nacional del Antártico. Instituto Antártico Argentino; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: La Mesa, Mario. Consiglio Nazionale delle Ricerche. Istituto Di Scienze Marine; Italia Fil: Moreira, María Eugenia. Ministerio de Relaciones Exteriores, Comercio Interno y Culto. Dirección Nacional del Antártico. Instituto Antártico Argentino; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina

Feeding habits of early life stages of the channichthyid Chionodraco hamatus were investigated on samples collected in the western Ross Sea in early summer of 1996 and 2004. The stomach content analysis was carried out on larval and postlarval specimens ranging from 14 to 39 mm SL. Unlike larvae and juveniles of other channichthyids, which elsewhere largely rely on early life stages of Antarctic krill or ice krill, no euphausiids were found in the stomach contents of C. hamatus, except for a single large individual of Thysanoessa macrura. In both years, dietary composition consisted almost exclusively of notothenioid fish larvae. Early larvae of Pleuragramma antarcticum overwhelmingly dominated the diet in terms of abundance, biomass and frequency of occurrence, accounting for 98.4% of the index of relative importance (IRI). Other fish larvae consumed occasionally in small amount were Trematomus lepidorhinus, T. scotti and C. hamatus itself. As a result, the feeding strategy of C. hamatus was considerably shifted toward specialization, relying on relatively few taxa of prey, each of them showing a high prey-specific abundance. Comparing both dietary composition and feeding strategy of C. hamatus in the two different sampling years, several differences were observed, probably due to different environmental conditions, mainly linked to a significant delay of ice retreat and formation of the Ross Sea polynya verified in the 2003-2004 summer season.

Age and growth of ocellated icefish, Chionodraco rastrospinosus, were investigated using counts of annual growth increments from sagittal otoliths. Samples were collected during research surveys by benthic trawl carried out around Elephant and South Shetland Islands in January–February 2002 and December 2006–January 2007. A total of 290 specimens were selected for the study, consisting of 120 females and 170 males. The age of fish was estimated by counting annuli on transverse sections obtained by grinding and polishing whole otoliths embedded in epoxy resin. The precision-of-age estimates within and between readers were tested applying both the average percent error (APE) and the coefficient of variation (CV). The estimated age-range was 1–12 for both sexes of C. rastrospinosus. Applying the von Bertalanffy growth function to the age–length data, a growth curve was obtained for each sex. The estimated values of VB growth parameters L ∞ and k were, respectively, 47.9 cm and 0.28 for females and 42.9 cm and 0.36 for males. Compared to other congeneric species, the growth performance of C. rastrospinosus was relatively high, being 2.82 and 2.81 in males and females, respectively. Age at sexual maturity was estimated to be about 4 years in both sexes. C. rastrospinosus captured in the studied area consisted mainly of adult specimens between 3 and 8 years, with few older fish.

The otolith microstructure of juvenile Scotia Sea icefish (Chaenocephalus aceratus) was analyzed from samples collected around Elephant and South Shetland Islands, with the aim to validate previous annual ageing and to give new insight into its early life history timings. Fish were caught by bottom trawl fishing conducted on the continental shelf between 100 and 500 m depth. To determine the timing and position of the first annulus on sagittal otoliths, microincrements were counted on juvenile otoliths previously aged 1+ year old by counting annuli in sectioned otolith. Assuming that microincrements were laid down daily, age ranged from 406 to 578 days in fish measuring 13–19 cm TL, thus corroborating previous results. The relationship between fish size and otolith size/weight was estimated using the least square linear regression method. The relationship between age and otolith size was also estimated to determine the otolith length in 1-year old fish, which was approximately 1.58 mm. In all samples the otolith core was characterized by an evident strong check, assumed to be laid down at the beginning of exogenous feeding of yolk sac larvae. The yolk sac duration estimated from hatch to the first feeding check was longer than other channichthyids, lasting 29–45 days. Hatching dates were backcalculated from the date of capture using the age estimates, indicating C. aceratus sampled off Elephant and South Shetland Islands hatched over a long period lasting from July to December, with a peak in November. As a result, the potential larval dispersion driven by local oceanographic features is discussed.

Juvenile Antarctic toothfish (Dissostichus mawsoni) collected off the South Shetland Islands (CCAMLR Subarea 48.1) were aged by counting the presumed daily increments in the sagittal otoliths. The timing and position of the first annulus was examined for each individual fish from 10 to 13 cm TL. Under reflected light at low magnification, the otolith sections exhibited a wide opaque nucleus, with no evidence of deposition of the first translucent zone. The average measurement of ventral and dorsal radii of these sections were, respectively, 603 and 768 μm, consistently less than the measurements done in previously estimated 1 year old fish caught in the same area. All specimens aged in the present study were approximately 1 year old fish, with an age range between 365 and 431 days, suggesting a significant underestimation of age in the previous studies. The value of ageing precision indices calculated was relatively low, supporting the reliability of the reading technique applied. Two checks were easily identified in the core of all otolith sections, interpreted tentatively as hatching and first exogenous feeding checks. Back-calculating from the time of capture, the hatching period of D. mawsoni was estimated to occur throughout the summer season, from November to February. In conclusion, the delay in timing of deposition of the first translucent zone, which occurs in the second winter from hatching, should be taken into account in future studies on ageing Antarctic toothfish, as well as in the stock assessment models based on length at age data.

In comparison with other bathydraconids, all species of the genus Bathydraco are poorly known from an ecological perspective. The diet of juvenile Bathydraco marri Norman, 1938 was studied for the first time in specimens collected in the southwestern Ross Sea during summer 1998. Fish were collected in a single otter trawl catch at 330–340 m depth. The stomach content analysis showed that this species fed exclusively on crustaceans. Overall, 20 prey taxa were identified to genus or species level. Mysids, amphipods and copepods were the most important prey in decreasing order of importance. Other prey, such as Euphausia superba, isopods and tanaids were eaten occasionally and in very small amounts. A multivariate analysis was applied to feeding data to assess ontogenetic or sex-related changes in diet. No difference was detected between sexes, whereas diet of small and large fish differed in some degree. An ontogenetic shift from small and pelagic crustaceans such as copepods to benthic–benthopelagic prey such as amphipods and mysids was observed. Relating present results with published data on physiological characteristics of B. marri, it was possible to infer their feeding behaviour and mode of life. Like other bathydraconids, this species appeared to be an inactive and sluggish fish, which relied on more or less motile benthic or epibenthic prey adopting a “sit and wait” feeding strategy. On the other hand, smaller fish seem to be more active, feeding also on pelagic prey such as copepods that can be seasonally abundant, thus reducing the intraspecific competition for food.

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.

A new species of Antarctic plunderfish, Artedidraco glareobarbatus, has recently been identified from two specimens collected in the Ross Sea. On the basis of additional material composed of two specimens and a new colour morph, meristic and morphometric data of the species is updated. A complete set of measurements and counts was made on the new specimens following the previous authors. An accurate description of the mental barbel, which represents a key diagnostic character in this family, is provided. In particular, on the basis of external morphology of skin of the terminal expansion, two different types of mental barbel can be distinguished: a typical form as described in the holotype and paratype, and a new form, found in two specimens, with the terminal expansion consisting of irregular processes similar to flattened and convoluted ridges separated by deep furrows. Finally, the new colour morph, represented by a spotted specimen, is also described in detail.