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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.

The adoption of parental care behaviours is the distinctive reproductive characteristic associated with the diversification and divergence of notothenioid fishes into an array of habitats in the subzero shelf and upper slope waters around Antarctica and sub-Antarctic environments. These include a variety of pre- and post-fertilization activities, including courtship behaviour and mate choice, linked to the development of sexually dimorphic traits, nest construction and egg guarding until hatch. Using published literature and new data, this review synthesizes and evaluates, in a phylogenetic context, information related to parental care, specifically sex-specific morphological adaptations, nest location and structure, sexual differences in egg guarding and post-spawning mortality, duration of egg incubation times and larval size at hatch. The existence of parental care in phylogenetically basal notothenioids is not documented and unlikely; however, the derived lineages of the Antarctic clade (cryonotothenioids), especially bathydraconids and channichthyids, clearly exhibit a trend towards larger egg size and reduced fecundity that are considered proxies for parental care behaviours. In addition, the reproductive strategies of cryonotothenioids exhibiting parental care show latitudinal patterns at intra- and inter-specific levels. Antarctic species spawn in spring-summer and have low fecundity, large egg size at spawning and large larvae at hatching. Sub-Antarctic species spawn in autumn-winter and have moderate to high fecundity, moderate egg size and larval size at hatching, whereas non-Antarctic species spawn in winter and possess high fecundity, small egg size at spawning and small larvae at hatching.

The genus Chionodraco includes three morphologically similar species, two of them (C. hamatus and C. myersi) living sympatrically in the Eastern Antarctica, and the third one (C. rastrospinosus) being distributed in the Western Antarctica along the southern Scotia Arc. The few overlapping diagnostic characters are often useless for the right taxonomic identification of three species, complicated by the presence of hybrids between them. In the present study, we tested the discrimination power of sagittal otolith shape as a tool to distinguish among these closely related species. An array of shape indices and elliptic Fourier descriptors were individually obtained from sagittal otoliths and analysed using three different models for species classification: Linear Discriminant Analysis (LDA), Random Forest (RF) and K-nearest neighbour (KNN). According to the characteristics of the adopted metric (precision), none of the methods resulted to be the absolute best approach as the performance largely varied with the species. The overall precision was 63 %, 66 % and 70 % for LDA, RF and KNN respectively, so that KNN can be considered the best classifier model. As expected, C. myersi was the best recognized species by all classifier models, consistently with its morphological and phylogenetic difference from the other two species. Taking into account the observed pattern of otolith morphology of the three species and their own geographical distribution, we were able to evaluate the role of genetic, endogenous or environmental components in influencing otolith size and shape.

A recent population hypothesis for Antarctic silverfish (Pleuragramma antarctica), a critical forage species, argued that interactions between life history and circulation associated with glacial trough systems drive circumpolar distributions over the continental shelf. In the Ross Sea, aggregations of eggs and larvae occur under fast ice in Terra Nova Bay, and the hypothesis predicted that dispersing larvae encounter outflow along the western side of Drygalski Trough. The outflow advects larvae towards the shelf-break, and mixing with trough inflow facilitates return toward the inner shelf. To examine the hypothesis, we compared samples of P. antarctica collected near Coulman Island in the outflow, along Crary Bank in the inflow, and a third set taken over the rest of the Ross Sea. We ruled out misidentification using an innovative genetic validation. Silverfish larvae comprised 99.5% of the catch, and the highest population densities were found in Drygalski Trough. The results provided no evidence to reject the population hypothesis. Abundance indices, back-calculated hatching dates, length distributions and growth were congruent with a unified early life history in the western Ross Sea, constrained by cryopelagic early stages in Terra Nova Bay. By contrast, a sample in the Bay of Whales revealed much smaller larvae, suggesting either a geographically separate population in the eastern Ross Sea, or westward connectivity with larvae spawned nearby by fish sourced from troughs upstream in the Amundsen Sea. These results illustrate how hypotheses that integrate population structure with life history can provide precise spatial predictions for subsequent testing.

Antarctic plunderfishes are demersal species inhabiting the continental shelf of the Ross Sea, with sympatric distributions and similar morphology. Assuming these species are potential competitors for food, we aimed to quantify food overlap among them and to test the existence of factors involved in prey resource partitioning. Dietary composition and feeding niche breadth were estimated through stomach contents analysis of some species of Artedidraco sampled in the western Ross Sea. The fish community consisted of a wide range of feeders, from specialists like A. glareobarbatus and A. shackletoni, which fed exclusively on epifaunal polychaetes, to generalists like A. loennbergi and A. skottsbergi, which fed on a variety of prey. Although all species relied exclusively on benthic prey, diet diversity and prey type largely differed from each other, both contributing to reduce prey overlap and food competition. In a few cases, relatively high food overlap was observed between species with different spatial distributions. Based on our data and on previous studies, prey resource partitioning in plunderfishes is therefore established through morphological and behavioural adaptations, either by differential development of sense organs and trophic structures or by different diet composition and spatial distribution within the shared benthic habitat.

The present study provides the first estimate of the daily ration for a goby species in the Mediterranean Sea, using a new approach to determine the mass of fish stomach contents through the sum of individual prey dry mass derived indirectly from prey size. Diel feeding activity and daily ration of the pelagic goby Aphia minuta were studied under natural conditions in the coastal waters off Comacchio (Northwestern Adriatic Sea) during the spring season. A total of 318 individuals of A. minuta, collected by 14 trawls carried out on 4 consecutive days, was examined for gut contents. The diel pattern of the vacuity index and the stomach fullness index indicated that A. minuta has nocturnal feeding behaviour. The daily ration, computed over a period of 16 h, was equivalent to 2.23% wet body mass.

The Bransfield Strait and adjacent waters represent one of the most important areas of larval retention off the Antarctic Peninsula. The species composition of larval fish assemblages has been described in detail in previous surveys carried out in the area, but the role of environmental parameters influencing the spatial distribution of early life stages was poorly known. By applying generalized additive models and multivariate analyses, we evaluated the role of environmental variables in shaping the small‐scale distribution of larval fish and investigated the spatial structure of the larval assemblage. It consisted of a few dominant notothenioid species, such as Champsocephalus gunnari, Lepidonotothen squamifrons, Lepidonotothen larseni, Pleuragramma antarctica and Trematomus scotti, and several other rarely caught species. Sea water temperature, salinity and sampling depth were the most important factors determining the spatial distribution of fish with different relative contributions, together explaining more than 80% of total deviance observed. Species richness was mostly affected by salinity, probably due to the narrow range of salinity preference by the species. Cluster analysis of abundance and presence data identified six and five distinct groups, respectively, each of them with substantial contributions of single or rarely two species. Differences in reproductive strategies of adult populations and spatial distribution of early life stages driven by different larval behaviour in response to environmental factors contribute to maintaining a well‐structured larval fish assemblage, ensuring spatial and food niche partitioning.

The non-Antarctic Notothenioidei families, Bovichtidae, Pseudaphritidae and Eleginopsidae, diverged early from the main notothenioid lineage. They are important in clarifying the early evolutionary processes that triggered notothenioid evolution in the Antarctic. The early-diverged group represents 8% of all notothenioid species and never established themselves on the Antarctic shelf. Most attention has been paid to the Antarctic notothenioids and their limited physiological tolerance to climate change and increased temperatures. In this review, we discuss key life history traits that are characteristic of the non-Antarctic early-diverged notothenioid taxa as well as the genetic resources and population differentiation information available for this group. We emphasise the population fitness and dynamics of these species and indicate how resource management and conservation of the group can be strengthened through an integrative approach. Both Antarctic waters and the non-Antarctic regions face rapid temperature rises combined with strong anthropogenic exploitation. While it is expected that early-diverged notothenioid species may have physiological advantages over high Antarctic species, it is difficult to predict how climate changes might alter the geographic range, behaviour, phenology and ultimately genetic variability of these species. It is possible, however, that their high degree of endemism and dependence on local environmental specificities to complete their life cycles might enhance their vulnerability.

Among the endemic notothenioid fish of Antarctica, the Antarctic silverfish (Pleuragramma antarcticum) is the only species in which all developmental stages live throughout the water column. It is widely distributed in the shelf waters around the continent, inhabiting both open waters and areas of pack ice at depths from 0 to 900 m. In successfully occupying this habitat, it evolved a suite of specific biological, ecological and physiological adaptations to the environmental conditions in the cold and highly seasonal Antarctic waters. Specialization for the pelagic environment evolved over millions of years enabled life under unusual environmental constraints and colonization of the pelagic realm of the Antarctic continental shelf. A sudden change of environmental conditions driven by the current rapid climate change could negatively affect this weak equilibrium, with a catastrophic cascade effecting higher trophic levels. Indeed, as both adults and early life stages of the Antarctic silverfish appear to be strongly dependent on sea-ice, this species would be especially sensitive to climatic or oceanic changes that reduce the extent of sea-ice cover or the timing of formation of coastal polynyas.

We measured the otolith chemistry of adult Scotia Sea icefish ( Chaenocephalus aceratus ), a species with a long pelagic larval phase, along the Antarctic Circumpolar Current (ACC) and compared the chemistry with simulated particle transport using a circulation model. Material laid down in otolith nuclei during early life showed (i) strong heterogeneity between the Antarctic Peninsula and South Georgia consistent with a population boundary, (ii) evidence of finer-scale heterogeneity between sampling areas on the Antarctic Peninsula, and (iii) similarity between the eastern and northern shelves of South Georgia, indicating a single, self-recruiting population there. Consistent with the otolith chemistry, simulations of the large-scale circulation predicted that particles released at depths of 100–300 m on the Antarctic Peninsula shelf during spring, corresponding to hatching of icefish larvae from benthic nests, are transported in the southern ACC, missing South Georgia but following trajectories along the southern Scotia Ridge instead. These results suggest that the timing of release and position of early life stages in the water column substantially influence the direction and extent of connectivity. Used in complement, the two techniques promise an innovative approach for generating and testing predictions to resolve early dispersal and connectivity of populations related to the physical circulation of oceanic systems.

Age and growth of the black scorpionfish, Scorpaena porcus , were estimated for different populations inhabiting natural reefs and artificial structures (artificial reefs and offshore gas platforms) in the northwestern Adriatic Sea. Annual growth increment counts were carried out on sagittal otoliths of 415 specimens ranging from 80 to 280 mm TL. The accuracy of age estimates was assessed by testing the annual deposition of annuli and the location of the first annulus by marginal increment analysis and daily growth increment counts, respectively. As commonly observed in other scorpaenids, annuli consisted of an alternating pattern of opaque and translucent zones. Marginal increment analysis confirmed that annuli are formed once a year, with opaque zones laid down in spring-summer and translucent zones laid down in autumn-winter. The precision of age estimates was tested by applying both the average percent error (APE) and the mean coefficient of variation (CV). The maximum age estimated for the whole sampled populations was 8 years. The von Bertalanffy growth curves were separately fitted for natural and artificial reef populations of S. porcus . The likelihood ratio test indicated that the overall von Bertalanffy growth curves differed significantly between the two populations. The instantaneous growth rate ( k , year -1 ) and asymptotic length (L ∞ , cm) were 0.23 and 22.30 and 0.53 and 20.13 for natural and artificial reef populations, respectively. Compared with natural reef population, populations of S. porcus inhabiting artificial reefs and, particularly, offshore platforms, were characterized by larger and older fish. However, young-of-the-year were completely absent from the platform habitats. The effects of artificial structures on S. porcus populations in the study area are discussed in the light of previous results on scorpionfish living in other areas.

De Buen’s goby, Buenia affinis , is a very small Mediterranean goby (38.8 mm TL) inhabiting sandy infralittoral bottoms and known only from a few published records. Some aspects of reproduction and growth of B. affinis were investigated from a population collected in the Kvarner area (north-eastern Adriatic Sea). Sampling was carried out by SCUBA diving between May 2003 and April 2004. The sex ratio did not differ significantly. The estimated length at sexual maturity was 26.1 and 27.4 mm for females and males, respectively. The spawning season extended from February to July. The absolute fecundity (F) ranged from 457 to 714 eggs per individual (mean ± SE, 556 ± 25). Based on the length frequency distribution analysis throughout the year and seasonal growth bands on sagittal otoliths, B. affinis was assumed to be an annual species.

The pattern of genetic variability of two species of Mediterranean gobiids was compared, with reference to their different life history traits (Aphia minuta paedomorphic and pelagic; Gobiusniger metamorphosed and benthic). The aim was to evaluate how different life histories can affect the genetic structure in these marine teleosts. The study was carried out on populations of both species sampled in the western Mediterranean and in the Adriatic Sea. Seven restriction endonucleases were used for the RFLP analysis of a mitochondrial DNA segment comprising the NADH dehydrogenase subunits 3, 4L and 4. The results highlighted two different patterns of genetic variation, a weak genetic structure in A. minuta and population subdivision in G. niger. These observations may be explained not only in terms of the different dispersal capabilities of these species, but also considering that A. minuta is an abbreviate iteroparous spawner while G. niger is a protracted iteroparous spawner. Because abbreviate iteroparity is a reproductive strategy selected in stable environments with high resource availability, Pliocene and Pleistocene climate oscillations may have represented factors that negatively influenced the reproductive success of A. minuta, producing demographic fluctuations and bottlenecks, as suggested by the mismatch distribution analysis. The weak genetic structure of A. minuta populations seems to be therefore due to a more recent re-colonization of the Mediterranean basin after a severe population decline, rather than to the high vagility of this pelagic goby.

The early life history of the black anglerfish, Lophius budegassa was investigated by otolith (lapilli) increment analysis. Samples of demersal juvenile L. budegassa ranging from 54 to 196 mm total length were collected during bottom trawl surveys in the central Adriatic Sea. By counting increments presumed to be deposited daily in the lapillar otoliths, 88 specimens of L. budegassa were successfully aged. Age estimates of juveniles ranged between 79 and 204 days, indicating that probably the pelagic phase of this species is relatively short and settlement occurs at less than 3 months of life. The analysis of check marks in the core area of lapilli enabled us to determine the period of endogenous feeding, which would last between 15 and 24 days after hatching. Back-calculated hatching dates and, consequently, the spawning season of L. budegassa in the Adriatic Sea was spread over a long period, lasting at least from February to June. The length at age relationship gave an estimate of mean growth rate of approximately 0.8–1.02 mm/day, indicating a faster growth rate of 0+ juveniles L. budegassa than previously thought. The implications of these findings on age estimates discrepancies between previous ageing studies on L. budegassa carried out using different calcified structure (sagittae or illicia) are discussed.

Age and growth of the brown meagre Sciaena umbra (Sciaenidae) collected (n = 532) in the north-western Adriatic Sea was studied by means of transverse otolith sections. The maximum age estimated was 19 and 16 years for males and females, respectively. The length at age estimated for each sex indicated that females attain a larger size and grow slightly faster than males. Both marginal increment analysis and edge analysis confirmed that annuli are formed once a year, with opaque zones laid down in summer (June-July). Age readings were very precise, with a percentage agreement of 98% between readers and low values of the index of average percent error (0.9%) and coefficient of variation (1.3%). Von Bertalanffy growth function was fitted to age-length data, and growth parameters were estimated for males (L∞ = 44. 9c m;k = 0.27, t0 = −2.17 years) and females (L∞ = 47. 2c m;k = 0.28, t0 = −1.82 years). In both sexes of brown meagre, growth rate was high until they attain 2-3 years of age, i.e. at sexual maturity. Most of catches were obtained in late summer-early autumn. On the basis of present data, the sampled population of brown meagre mostly consisted of small fish younger than three years of age (about 90%). In addition, landings of this species in recent years largely decreased. As reported elsewhere in north-western Mediterranean, brown meagre stock in the Adriatic Sea showed clear signs of depletion, thus specific management measures for this species are urgently required.

The early life stages of the Antarctic silverfish (Pleuragramma antarctica), an important prey species for higher predators in the Southern Ocean ecosystem, dominate the larval fish assemblages of the Bransfield Strait, one of the most important areas for larval retention off the Antarctic Peninsula. Nevertheless, the spatial location of areas where they were spawned and the timing of larval hatching remain unknown. By linking Lagrangian particle tracking simulations with age data obtained using otolith microincrements from fish caught north of Joinville Island in a pelagic survey, we estimated the distribution of hatch dates and subsequent growth rates of silverfish reaching the Bransfield Strait, and predicted the areas where they were spawned. Larval hatching peaked during the last week of December, and the inner shelf and shelf break, east of the Larsen Ice shelf, were the dominant areas predicted to contribute to larval assemblages in the Bransfield Strait. Over simulated periods of 600–630 days, 35–40% of particles remained within the Bransfield Strait, suggesting an important source of supply to higher predators feeding off the northern Antarctic Peninsula. The daily growth rate at the mean size of 22.3 mm was 0.18 mm, corresponding to a daily change in size of approximately 0.82% standard length (SL), and large variability in growth rate suggested a wide range of environmental conditions experienced during the period of advection from the spawning areas. These results provide spatial predictions that can be tested empirically in future studies, using the simulated trajectories to inform sampling design and spatial coverage.

The Western Antarctic Peninsula (wAP) is globally one of the systems most heavily impacted by climate change, notably steep declines in sea ice extent. In forage species, reproductive resilience to change is particularly important because population fluctuations are rapidly communicated through the system via trophic interactions. The reproductive traits of the ice-dependent forage species Antarctic silverfish (Pleuragramma antarctica) from different areas along the wAP and at the tip of the Antarctic Peninsula were investigated through macroscopic and histological analyses of gonads, with the aim to assess its reproductive potential and to test for spatial differences in fecundity and spawning season. Fish samples were collected in late summer off Charcot Island, in Marguerite Bay and off Joinville Island; no fish were caught in the central wAP. Samples from Charcot Island and Marguerite Bay consisted of adults in developing gonad stage, whereas those from Joinville consisted almost exclusively of juveniles. Mean GSI was relatively low (2–3%) and similar in both sexes, as specimens were still far from being actively reproducing. Developing females exhibited two discrete, though partially overlapping modes of oocytes of different size, with vitellogenic oocytes measuring 0.5–1.0 mm. Absolute and relative fecundity ranged between 3000 and 12,000 eggs per female and between 80 and 190 eggs·g−1, with a strong relationship between absolute fecundity and body size. These results were consistent with a single population at Charcot Island and Marguerite Bay and indicated substantial reproductive potential, which may mitigate population isolation and reductions in habitat availability but cannot ultimately offset catastrophic loss of spawning habitat linked to sea-ice retreat.

The microstructural analysis of the sagittal otoliths of juvenile Atlantic bluefin tuna, Thunnus thynnus , can be used to estimate the age and growth rate of young-of-the-year individuals born in the Mediterranean. Samples of juvenile bluefin tuna, obtained as by-catch of the local small-scale pelagic fishery for Atlantic bonito and dolphinfish, were collected off the northern coast of Sicily between late August and early November 2002. Otolith age readings were carried out on 56 specimens ranging between 195 and 400 mm fork length and between 112 and 1266 g total weight. Based on microincrement analysis along a counting path from the otolith core to the antirostrum, juvenile fishes were found to be between 77 days and 153 days old. The estimated growth rate was practically linear over the whole size range, accounting for about 2.0-2.37 mm/day. Derived from the length-weight relationship and the estimated length-at-age data, the mean weight-at-age was 168, 429 and 813 g for 2, 3 and 4 month-old juveniles respectively. Furthermore, the hatching date distribution of bluefin tuna, obtained by means of the back-calculation of ageing data, indicated a spawning period of at least two months, namely from mid-May to mid-July, with a peak in mid-June. Our data indicate that juvenile bluefin tuna have a very high growth rate in the first part of their life, reaching a weight of more than 1 kg in four months.

The transparent goby, Aphia minuta, is one of the few pelagic species of the family Gobiidae. Its geographic range covers the eastern Atlantic Ocean, from Gibraltar to Norway and the Mediterranean basin including the Azov and Black seas. However, it does not occur along the north African coasts. The species is characterized by a unique larval morphology and precocious sexual maturation, i.e. a type of heterochrony known as progenesis. The transparent goby is an annual species that lives less than 1 year, with a maximum size of less than 60 mm. The breeding season is quite long and spawning takes place at least twice during its short lifespan. Just after spawning, all breeders quickly die probably as a consequence of the degeneration of the intestinal epithelium by apoptosis, marking the end of the entire cohort. Spending most of its life in the water column, it is a planktotrophic feeder, relying mainly on small copepods. In turn the transparent goby is preyed on by several species of fish and larger cephalopods. During ontogenesis, t hree phases characterize the species: a “pelagic phase”, composed of larval stages hatched from demersal eggs that inhabit shallow coastal waters; an “aggregated phase”, composed of juveniles that gather in schools in shallow waters during winter; finally, a “demersal phase”, composed of adults that in spring migrate offshore with a more dispersed distribution in proximity of the bottom. Despite its small size, this species is largely exploited by local small-scale fisheries developed mainly in the western and central Mediterranean. The fishing fleets, harboured in several sites in Spain and Italy, are generally composed of small vessels. Most of them use very selective gear such as purse-seine nets to catch schools of the transparent goby during winter. For these artisanal fisheries, the transparent goby represents, although seasonally, a very important source of income, yielding locally up to more than 100 tons per fishing season and 75 kg/vessel/day. This review critically examines the published literature on the biology and fisheries of the transparent goby, aiming to provide useful tools for appropriate management and for a sustainable exploitation of this important resource.

The feeding ecology of the transparent goby Aphia minuta was examined in spring (May 2003) in the coastal waters off Comacchio, in the northwestern Adriatic Sea. Stomach content analysis indicated A. minuta to be a planktivorous species, feeding exclusively on pelagic invertebrates. The diet composition was dominated by the calanoid copepods Acartia clausi and Temora longicornis, followed in decreasing order of importance by other copepods (especially calanoids and Oncaea spp.) and larvae of decapods, polychaetes and bivalves. A. minuta exhibited a generalistic feeding strategy with a relatively broad niche width. Abundant taxa in the environment, such as A. clausi and T. longicornis, were seldom selected, whereas rare taxa, such as larvae of polychaetes and decapods, were highly selected. According to the observed ontogenetic shift in diet, small-size individuals relied preferentially on juvenile T. longicornis and Oncaea spp., whereas large-sized specimens consumed preferably A. clausi and calanoids. The positive relationship found between prey and fish size may help to mitigate the intraspecific competition for food resources.