Age estimation and lead�Cradium dating of Antarctic toothfish (Dissostichus mawsoni) in the Ross Sea

Antarctic toothfish (Dissostichus mawsoni) are the target of an important commercial fishery in the Southern Ocean, yet age data used for management have not been comprehensively tested for accuracy. In this study, Antarctic toothfish were aged using counts of otolith growth zones based on criteria established for Patagonian toothfish, D. eleginoides, a closely related species. To validate these ages, the radioactive disequilibrium of lead-210 and radium-226 in otolith cores was measured and used as an independent chronometer to accurately determine age across the range of fish caught in large numbers by the fishery. Growth-zone counts indicated Antarctic toothfish live to at least 39 years of age, and were in close agreement with the chronometer, validating the age estimation criteria and the accuracy of age estimates. Von Bertalanffy growth function parameters indicated Antarctic toothfish were relatively slow-growing (k = 0.111), especially in relation to their maximum size (L _∞ = 158.9 cm).     

Age and early life history of juvenile scotia sea icefish, <Emphasis Type="Italic">Chaenocephalus aceratus</Emphasis>, from Elephant and the South Shetland Islands

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.     

The two giant sister species of the Southern Ocean, <Emphasis Type="Italic">Dissostichus eleginoides</Emphasis> and <Emphasis Type="Italic">Dissostichus mawsoni</Emphasis>, differ in karyotype and chromosomal pattern of ribosomal RNA genes

The two giant notothenioid species, the Patagonian toothfish Dissostichus eleginoides and the Antarctic toothfish D. mawsoni, are important components of the Antarctic ichthyofauna and heavily exploited commercially. They have similar appearance and size, both are piscivorous and bentho-pelagic, but differ in their geographic distribution and absence/presence of the antifreeze trait. We karyotyped these two sister species by analyzing specimens collected from multiple Antarctic and sub-Antarctic sites. Both species have a diploid number of 48, but differ in karyotypic formula, (2m + 2sm + 44a) for D. eleginoides and (2m + 4sm + 42a) for D. mawsoni, due to an extra pair of submetacentric chromosomes in the latter. Chromosomal fluorescence in situ hybridization with rDNA probes revealed unexpected species-specific organization of rRNA genes; D. mawsoni possesses two rDNA loci (versus one locus in D. eleginoides), with the second locus mapping to its additional submetacentric chromosome. The additional rRNA genes in D. mawsoni may be a cold-adaptive compensatory mechanism for growth and development of this large species in freezing seawater.     

Otolith shape analysis and daily increment validation during ontogeny of larval and juvenile European chub Squalius cephalus

This assesses features of otoliths from laboratory-reared embryos, larvae and juvenile European chub Squalius cephalus from hatching to 180 days post-hatching (dph). We observed the development of the three pairs of otoliths (lapilli, sagittae and asterisci) and more precisely shape changes, as well as timing and deposition rate of increments of the lapilli. The lapilli and the sagittae were present at hatching, whereas the asterisci formed between 20 and 30 dph. The lapillus and sagitta shapes were round until 20 dph. From 60 dph the anterior and the posterior rostra of the sagittae were well developed, but very thin, making this otolith too fragile to manipulate for further studies of shape and validation of otolith increment deposition rate. The lapilli provided reliable age estimates for free embryos, larvae and juveniles up to 120 dph. However, caution should be taken when ageing fish older than 150 dph as an underestimation was noticeable. The regression of the number of otolith increments on age showed a slope and an intercept not significantly different from 1 and 0, respectively, which indicated that otolith growth increments were deposited on a daily basis, with the first microincrement occurring at hatching. Increment counts were consistent between three interpreters, indicating a consistent and reliable age estimate. This study validates that the otolith increment deposition rate can be used to assess hatching dates and daily growth of wild S. cephalus under 150 dph and in environments similar to the conditions used in this study.     

The timing of early life events and growth rate estimates of age‐0 year group brill Scophthalmus rhombus along the west coast of Ireland

The timing of spawning and hatching, larval durations and growth exhibited by juvenile brill Scophthalmus rhombus captured along the Irish west coast were estimated using otolith microstructure analysis. Scophthalmus rhombus were estimated to have hatched between February and May, with fish settling onto nursery grounds between March and June. Fish collected later on in the season exhibited higher otolith growth rates in comparison to earlier collected fish. This is the first study to describe the early life history of a commercially valuable but understudied flatfish species.     

Cytomorphology of female and male gonads in Antarctic toothfish <Emphasis Type="Italic">Dissosctichus mawsoni</Emphasis> (Nototheniidae) from the Ross Sea in the summer period

Results of histological analysis of gonads of female and male Antarctic toothfish Dissostichus mawsoni caught in the Ross Sea of the Pacific sector in the period of Antarctic summer (December–February) 2004–2005 are presented. Morphological indices and index of gonad maturity are described and ecological criteria of assessment of maturity stages of ovaries, cytological indices of oocytes, and the type of toothfish oogenesis are determined. It was established that in the period of fishing Antarctic toothfish, females and males with gonads at maturity stage III dominate. Ovaries contain two groups of oocytes of the period of trophoplasmatic growth and large oocytes of the nearest spawning season that comprise the smallest proportion of total sex cells. In the testes of two male toothfish, the primary fusion of renal and generative tissues was revealed. It is suggested that the termination of gonad maturity of toothfish takes place from March to April, and spawning takes place from June to August.     

Estimating the timing of growth rings in Atlantic cod otoliths using stable oxygen isotopes

A technique involving micro‐scale sampling of otolith carbonate and analyses of stable oxygen isotope composition was used to relate the zone appearance of the otolith to the seasonal temperature cycle. Otolith opacity could then be related to the timing of zone formation. Otoliths from two groups of Atlantic cod Gadus morhua held under known temperature conditions over a period of 4 and 6 years were examined. The otolith translucency followed the same pattern as the estimated temperature (from otolith δ¹⁸O values) in the yearly increments three and four, meaning that the translucent zones were deposited at the seasonal highest temperature in late summer and early autumn. The relative light intensities of otolith yearly increments five and six of older fish (deposited in the same years), however, were not significantly correlated to the estimated temperatures since increased otolith translucency also occurred at low temperatures. This might have been caused by stress in connection with gonad development or starvation during the spawning period. The results showed that this method of coupling otolith opacity and stable oxygen isotope composition can be used to estimate the timing of zone formations in otoliths.     

Preliminary estimates of the age and growth of immature smooth oreo Pseudocyttus maculatus Gilchrist 1906 (Oreosomatidae) in the Falkland Islands region of the South Atlantic

Sectioned otoliths were used to estimate the age of 29 specimens of the smooth oreo (Pseudocyttus maculatus Gilchrist 1906) from the Falkland Islands region of the South Atlantic. This represents the first ageing study of this species in this region of the world. All specimens were immature (sub-adults), the largest having a maximum total length of 347 mm. Growth increments were observed in sectioned otoliths and assumed to be annual in periodicity. The maximum age estimate of individuals in this study was 20 years and the form of somatic growth was similar to previous research on this species from Australian waters. The otolith microstructure consisted of an inner, mostly opaque zone with wide increments followed by an outer, mostly translucent zone with narrower increments. It is suggested that these zones correspond to the two growth phases in the life history of this species, namely the pelagic juvenile phase (opaque zone) and the demersal sub-adult/adult phase (translucent zone). Received: 27 May 1997 / Accepted: 31 October 1997     

Seasonal changes in the physiology of brook trout, Salvelinus fontinalis (Mitchill), in a sub-Arctic river system

Wild herring larvae were sampled from the Firth of Clyde, Scotland in 1980 and 1981 to assess the suitability of otolith ageing methods for herring larval studies. The ages and growth rates were estimated directly from otolith ring counts, by comparison of ring counts with the results of validation studies on reared larvae of known age, and by back-calculation. Growth rates based on otolith data were compared with indirect calculations based on length at capture. The assumption of daily ring deposition, even allowing for a period of lag before the initiation of daily ring deposition, led to incorrect predictions for age at yolk-sac absorption, and back-calculations led to overestimated growth rates, indicating that ring deposition does not begin at hatching and that light microscope counts give a rate different from one ring per day in wild herring larvae.     

Validation of yellowedge grouper, <Emphasis Type="Italic">Epinephelus flavolimbatus</Emphasis>, age using nuclear bomb-produced radiocarbon

Age validation and estimates of longevity of yellowedge grouper (Epinephelus flavolimbatus) from the Gulf of Mexico (GOM) are needed to inform fishery management decisions. Yellowedge grouper sagittal otoliths (n = 100) were collected, aged using conventional means, and cores were submitted for radiocarbon (¹⁴C) measurement. Radiocarbon values of yellowedge grouper otoliths were compared to established radiocarbon chronologies in the region to validate the age and ageing methodology of this species. The yellowedge grouper chronology displayed a similar sigmoidal trend as previously published chronologies. In addition to the core analysis, multiple areas on otolith sections from eight specimens were analyzed for Δ¹⁴C to validate age estimates for fish born prior to the ¹⁴C increase. Our results indicate that yellowedge grouper live longer than previously reported (minimum of 40 years based on radiocarbon measurements). The validated ageing methodology supported an estimated maximum longevity of 85 years and established that yellowedge grouper have the longest lifespan currently known for any species of grouper in the GOM. Results also indicate a depth-age interaction in that material extracted from adult otolith sections assigned to post-bomb dates exhibited lower Δ¹⁴C values than cores (juvenile material) assigned to the same post-bomb dates. This finding is likely explained by lower ¹⁴C levels reported from water masses at deeper depths (>100 m) which are inhabited by adults.     

Validation of daily increment formation in otoliths for Gymnocypris selincuoensis in the Tibetan Plateau,China

Daily increment validation in fish otolith is fundamental to studies on fish otolith microstructure, age determination and life history traits, and thus is critical for species conservation and fishery management. However, it has never been done for Schizothoracine fish, which is the dominant component of fish fauna in the Tibetan Plateau. This study validated the daily increment formation of Gymnocypris selincuoensis, as a representative of Schizothoracine fish, by monitoring the growth of hatchery‐reared larvae group and wild‐caught post‐yolk‐sac larvae group under controlled experiments. The results from monitoring the hatchery‐reared larvae group showed that sagittae and lapilli were found in yolk‐sac larvae, and formed 5–7 days before hatching, but asterisci were not found until 11 days post‐hatching. The first increment in sagittae and lapilli was formed in the first day after hatching. The daily periodicity of increment formation was examined and confirmed in sagittae and lapilli of both larvae groups. However, sagittae were better for age determination than lapilli for larvae at earlier days. For larval G. selincuoensis older than 50 days, lapilli were the only otolith pair suitable for larvae daily age determination. This study validated the daily increment formation in Schizothoracine fish for the first time has primary implications to other fishes from this subfamily.     

Age and growth validation of the small spotted grunt Pomadasys commersonnii (Lacepède, 1801) from the northwestern coast of the Arabian Sea of Oman

Age structure and growth parameters were determined for a population of small spotted grunt, Pomadasys commersonnii in the Arabian Sea. Small spotted grunt samples were collected monthly between September 2007 and August 2008 by beam trawl [40 mm cod‐end mesh size] surveys conducted along the Arabian Sea coast of Oman from Ras Al‐Had in the north to the Oman‐Yemen border in the south west of Salalah between latitudes 16^o 33′N and 22^o 21′N and longitude 53^o 09′ and 59^o 55′ E and from depths of 20 to 250 m respectively. Marginal increment analysis of the sagittal otolith confirmed the deposition of annual increments on transverse sections, validating this technique for age and growth studies. Fish size (Fork Length, FL) ranged between 33–78 cm and age of fish ranged between 2 and 14 years with 5–9 years old fish comprising the majority of the catch. Both males and female exhibited asymptotic patterns of growth and the combined growth curve for both sexes provided von Bertalanffy growth (VBG) parameters of L_∞ = 77.2 cm FL (≡83.8 cm Total Length), k = 0.232/y and t₀ = ?0.058 y. VBG parameters, derived from Length‐Frequency Distribution Analysis (LFA) using ELEFAN1, PROJMAT and SLCA, obtained similar values (average values for the 3 methods: L_∞ = 78.8 cm FL, k = 0.35/y and t₀ = ?0.64 y) to those obtained from otolith analysis. A strong linear relationship was observed between otolith weight and age, and although age residuals ±4 years was observed between sagittal otolith age and estimated age (depending on sex and otolith weight), the results indicated that otolith weight could be used as a rapid proxy to estimate age and derive VBG parameters. In conclusion, both otolith ageing and LFA methods provided similar L_∞ and k values and the average values derived from all 4 methods lies within the auximetric plot for the species providing confidence in the VBG parameters obtained for small spotted grunt in the Arabian Sea.     

Validation of annual periodicity in otoliths of red snapper, <Emphasis Type="Italic">Lutjanus campechanus</Emphasis>

The periodicity of otolith growth increments (opaque and translucent zones) from adult red snapper (Lutjanus campechanus) was examined through a mark and recapture study (2005–2010), and laboratory holding of hatchery reared red snapper over a 2 year period (2002–2004). Wild red snapper (n = 295) were caught hook-and-line, marked with anchor tags, injected with oxytetracycline dihydrate (OTC), and released in the Gulf of Mexico 15–40 km south of Dauphin Island, Alabama. Marked fish were recaptured up to 2.8 years after release (n = 35) and sagittal otoliths were dissected, sectioned and examined under white and blue-violet light. The number of opaque growth zones past the OTC mark was compared to time at liberty for each fish and supported an annual periodicity of growth increment formation. Also, most (87%) of the hatchery reared fish showed two opaque zones that supported an annual increment formation rate. However, an unusual timing of opaque zone formation was shown for mark-recaptured fish. Based on known timing of OTC marking, otoliths from mark-recapture fish showed opaque zone formation from late summer (August) to early winter (December). This fall formation of opaque zones is in contrast to previous studies and its timing may relate to the end of spawning for this species.     

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

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

Estimation of migratory history in female masu salmon Oncorhynchus masou (Brevoort, 1856) with the growth hormone pseudogene

To estimate the migration timing, length, and location of females with the growth hormone pseudogene (GHp), trace element analyses were performed on the otoliths of 40 wild adult masu salmon, Oncorhynchus masou (12 males, 19 normal females, and nine females with GHp [all fish were 3‐ or 4‐years‐old]) caught during the reproductive season (September) from 2004 to 2010 in the Atsuta River in Japan. Sr concentrations at the end of the otolith translucent area formed during the winter suddenly increased in all individuals, suggesting that they had migrated in the spring. In addition, the estimated migration length and location of females with GHp indicated that they had spent a fixed period of 1 year in the ocean, suggesting that females with GHp have a similar migratory history as that of normal females.     

Proximate composition and energy density of nototheniid and myctophid fish in McMurdo Sound and the Ross Sea,Antarctica

Nototheniid and myctophid fish are primary prey for marine piscivores, yet little is known about their nutritional value. In this study, we characterized the proximate composition [PC: water, fat (neutral lipids), crude protein (CP) and ash] and energy density (ED; kJ g⁻¹) of fifteen fish species from McMurdo Sound and the Ross Sea, Antarctica. We assayed the entire fish for all species except for the large Antarctic toothfish, Dissostichus mawsoni (muscle tissue only). On a wet mass basis (WM), fish were variable in composition: moisture content ranged from 64.9 to 87.3% WM, fat from 0.5 to 17.4% WM, CP from 7.7 to 16.7% WM, ash from 11.2 to 21.0% FFDM (fat-free dry mass), and ED from 2.9 to 10.3 kJ g⁻¹. Myctophids and pelagic nototheniids such as Pleuragramma antarcticum and D. mawsoni were high in fat content (7–17% WM), while a bathylagid and benthic nototheniids including most Trematomus spp. and Lepidonotothen squamifrons were low in fat (0.5–4% WM). The epibenthic Trematomus species (T. eulepidotus and T. lepidorhinus) were intermediate. Energy density tracked fat content, with highest values in myctophids and pelagic nototheniids. The variation in nutrient and energy density confirms that prey composition must be taken into account when modelling energy and nutrient fluxes within the Antarctic ecosystem. Further analyses of prey collected over a number of different locations and seasons are needed in order to determine how the nutritional value of certain species might affect annual or decadal variation in reproductive success or population size of top predators.     

Age estimates derived from hard parts of swordfish Xiphias gladius from the north-western Mediterranean Sea

Accurate age estimates for fish are critical for properly understanding stock dynamics and health; this is particularly true for larger billfishes. Here we determined the most accurate aging estimation methods for swordfish (Xiphias gladius). We compared age estimates obtained from fin-ray sections, otolith sections, whole otoliths, and vertebrae collected from 87 swordfish off the east coast of Corsica. Age estimates from otolith sections were most consistently estimated across different readers (lowest average percentage error), followed by fin-ray sections, third vertebrae, and whole otoliths. When the age estimates from the otolith sections were compared with the other three age sclerochronological methods, we found the average percentage error to be lowest between the otolith section and fin-ray methods. However, age estimates from fin rays proved most useful for estimating swordfish younger than 6 years, as the fin ray-based age diverged from that of the otolith sections as the swordfish aged. Combining fin ray and otolith section techniques, we estimated the growth parameters of 1–12-year-old females (L_∞ = 259.412, k = 0.113, t₀ = −2.499) and 1–7-year-old males (L_∞ = 175.543, k = 0.202, t₀ = −2.239). We found that females grew significantly faster than males after 3 years and remained larger thereafter. Our calculated growth rates for this region of the north-western Mediterranean Sea were lower than those of the Atlantic, Pacific, and eastern Mediterranean Sea swordfish populations, and similar to growth rates recorded for the western Mediterranean Sea populations. Our study provides critical knowledge on biological-related parameters to serve as a guide for preserving the swordfish population in the Mediterranean Sea.     

基于形态分析探究鳞头犬牙南极鱼各生活史阶段耳石形态变化

鳞头犬牙南极鱼为南极最为重要的底层鱼类,具有重要的生态作用和极高的商业价值,鱼类耳石形态随着生活史过程的推移有所差异,故耳石形态分析可用于推断鳞头犬牙南极鱼的生活史过程。本研究利用采集自南极罗斯海、阿蒙森海、威德尔海及拉扎列夫海120尾分属4个生活史阶段的鳞头犬牙南极鱼耳石,结合传统测量分析与椭圆傅里叶分析两种形态学研究方法,对其各生活史阶段耳石形态的差异进行研究。结果表明: 鳞头犬牙南极鱼各生活史阶段耳石形态存在差异,随着生活史过程的推移,耳石的变化趋势为整体上由轮廓平滑、复杂度较低向轮廓曲折、高度复杂化转变,且纵轴方向增长速度低于横轴方向,翼叶等特征部位变化显著。针对耳石形态的线性判别分析结果显示,椭圆傅里叶分析判别值较高,为85.4%,而传统测量分析判别值较低,为71.9%,表明相较于传统测量分析,椭圆傅里叶分析更具优势。     

Age, growth, mortality and population characteristics of the pearl perch, Glaucosoma buergeri Richardson 1845, from deeper continental shelf waters off the Pilbara coast of north-western Australia

Pearl perch, Glaucosoma buergeri Richardson 1845, from deeper waters (> 100 m depth) on the continental shelf of north-western Australia were aged by examining transverse sections of their sagittal otoliths. Ages were assigned based on counts of alternating opaque and translucent zones (annuli). Otolith length and breadth (width) increased linearly with fish length, whereas otolith weight increased linearly with fish age. The continuous growth of the otoliths provides some evidence that the opaque and translucent zones used to estimate age in this study are formed on a regular basis. Parameters of the length–weight relationship were estimated, along with parameters of the von Bertalanffy growth function. The generalised von Bertalanffy growth function (total length-at-age, both sexes combined) for G. buergeri was L _t=512.7 (1 – e^{–0.139( t  + 0.89)}). There was no significant differential growth between the sexes in observed length-at-age. The oldest individual found was a male G. buergeri estimated to be 26 years of age. The annual instantaneous rate of natural mortality ( M ) was estimated to be 0.14. The slow growth, long life and low natural mortality rate indicate that G. buergeri is vulnerable to overfishing and that harvest strategies for this species should be conservative, given its low production potential.     

Rhythmic structural and chemical patterns in otoliths of the Antarctic fish Notothenia larseni: Their application to age determination

Summary Sagittal otoliths from Notothenia larseni contain microincremental growth rings which are distinctly visible in otolith sections using Scanning Electron Microscopy. These microincrements are similar to those deposited daily in the otoliths of fishes from temperate and tropical waters. Microincrements were easily enumerated and fish length was related to increment number by a logarithmic curve. Otolith microstructure analysis appears to provide a technique to accurately determine age and growth rates in these fish. Sr/Ca ratios in otolith aragonite were analyzed along a radius from the outside edge to the core of an otolith section using an electron microprobe. The strontium/calcium (Sr/Ca) ratios varied with a cyclic periodicity apparently related to seasonal water temperature cycles and the number of cycles agreed closely with age estimated from daily microincrement counts. Sr/ca cycles can potentially be used to determine age, validate growth rates determined by other methods, and establish thermal conditions experienced during the life of a fish. Microstructural and chemical analyses of otoliths demonstrate great potential in helping to answer many questions about the growth processes and ecology of Antarctic fishes.