Phosphorous (P) deficiency due to low P availability in fishmeal produced from blue whiting (Micromesistius poutassou) in feed for under-yearling Atlantic salmon (Salmo salar) smolt

Seawater transferred under-yearling Atlantic salmon (120 g) were fed a practical fishmeal formulated diet containing 57.4% blue whiting fishmeal and providing 15 g kg^− 1 total phosphorous (P) in the diet. The basal diet was supplemented with graded dietary levels of inorganic P (0, 3, 6, 9, 12 and 15 g kg^− 1) to total P levels of 15, 18, 21, 24, 27 and 30 g kg^− 1. Within a feeding period of 12 weeks, classical signs of P deficiency developed in Atlantic salmon fed the P un-supplemented diet containing 15 g kg^− 1 total P of natural origin. Deficiency signs included reduced growth and feed efficiency, reduced tissue mineral concentration (P, Ca, Mg, Zn), increased P:Ca ratio in the body, increased condition factor, metabolic disorder as indicated by lipid accumulation and impaired protein utilization, as well as reduced lipid, energy and Zn digestibility. Supplementation of inorganic P-salts in the diet at 3 g kg^− 1 (18 g kg^− 1 total P) significantly improved the production results with respect to growth and feed efficiency, and restored all other signs of P deficiency in fish. A higher supplementation level of 6 g kg^− 1 inorganic P (21 g kg^− 1 total P) was required for optimal mineralization in whole body and vertebrae. The highest supplementation levels of 15 g kg^− 1 added inorganic P (30 g kg^− 1 total P) seemed to increase P excretion and to have slightly negative impacts on growth and bone mineralization. Results suggest that P availability from blue whiting fishmeal is very low (3.2 g kg^− 1) and inadequate to meet dietary P requirement in rapidly growing under-yearling salmon immediately following seawater transfer, despite high natural P content in the blue whiting fishmeal.     

A numerical model of the dispersion of blue whiting larvae, Micromesistiuspoutassou (Risso), in the eastern North Atlantic

A numerical circulation and transport model system was used to simulate the dispersion of larvae of blue whiting, Micromesistius poutassou (Risso) in the eastern North Atlantic. The area of the model extends from the northern Bay of Biscay to the Norwegian Sea and covers the shelf-edge and adjacent waters at a horizontal resolution of around 20 km in 16 vertical layers. Larval input data were based on the long-term mean distribution, abundance and seasonal occurrence of larvae, derived from historical information. The circulation model was run using tidal forcing and climatological density fields as well as both climatological meteorological forcing and actual six-hourly wind stress fields for 1994 and 1995. Transport from the main spawning areas to the west of the British Isles and north of Porcupine Bank was associated with currents along the shelf-edge and in the Rockall Trough. Tracers were either dispersed to the north and north-east along the shelf-edge, extending into the northern North Sea and Norwegian Sea, or were retained in the Rockall Gyre and over Porcupine Bank. A less intense southerly flow from Porcupine Bank was observed both under climatological conditions and in the 1995 simulation, when winds were more variable than in 1994. The results based on the 1995 meteorological conditions showed the most extreme retention of tracers in the Rockall Trough/shelf-edge area west of Scotland and a low penetration of tracers onto the shelf. These results are discussed in relation to the observed distribution of 0-group juveniles and to indices of year-class strength – in particular, in relation to the 1995 year class, which is the highest year-class estimate of blue whiting on record.     

Migrations and hydrography determine the abundance fluctuations of blue whiting (Micromesistius poutassou) in the Barents Sea

The Barents Sea is the north‐eastern fringe of the distribution of blue whiting (Micromesistius poutassou). Fluctuations in distribution and abundance of blue whiting in the area have been marked. Two hypotheses are put forward to explain these fluctuations. First, rich year classes in the main Atlantic stock of blue whiting may contribute to increased abundance in the Barents Sea. Second, variations in hydrography, such as influx of warm Atlantic water, may be particularly important in this fringe area. We investigated these hypotheses using data from bottom trawl surveys conducted during the period 1981–2006. Variations in abundance (measured either as incidence or density) and distribution were correlated with recruitment in the Atlantic stock of blue whiting as well as hydrographic conditions. Regression analyses indicated that the abundance fluctuations are primarily determined by variations in recruitment of Atlantic blue whiting, a strong year class leading to high abundance in the Barents Sea the year after spawning. However, salinity anomaly in the Fugløya–Bear Island transect during the previous year, an indicator of high inflow of Atlantic water, had also a significant, positive effect. Thus, the data suggested a climatic modulation of dynamics that were primarily determined by recruitment of blue whiting in the main Atlantic stock. Analyses of size structure as well as earlier studies on population genetics supported this conclusion.     

Age and changes in growth of the king weakfish Macrodon atricauda (Günther, 1880) between 1977 and 2009 in southern Brazil

The coastal demersal sciaenid Macrodon atricauda (Günther, 1880), formerly M. ancylodon (Bloch and Schneider, 1801) was sampled for ageing during four periods (1977–1979, 1984–1986, 1997–1998 and 2006–2009) in commercial fishing and scientific surveys along southern Brazil (Lat. 30°S–34°40′S). Maximum observed age was seven years, but no fish over five years old was sampled in the last period. Marginal increment analysis of thin sections validated ageing and showed that opaque and translucent bands were laid down at all ages in spring–summer and autumn–winter, respectively. Ageing M. atricauda based on sectioned otoliths is highly recommended because comparisons with readings on whole otoliths showed that ages based on whole otoliths exceeded those based on sectioned otoliths for 56.5% of the aged specimens. The growth of M. atricauda has increased in the last four decades, most noticeably in the case of adult males over two years old and females over three years old. A threefold decrease in its density and the demersal fish community as a whole are the most likely causes of the growth increase.     

Development of a homologous radioimmunoassay for Mediterranean yellowtail (Seriola dumerilii, Risso 1810) LH

Purified Mediterranean (M.) yellowtail luteinizing hormone-like gonadotropin (MyLH) and its β-subunit (MyLHβ) served to develop a radioimmunoassay (RIA) for MyLH. The rabbit antisera against MyLH and MyLHβ used for this purpose were tested on pituitary sections by immunocytochemistry. Anti-MyLHβ specifically detected a single type of cells, which were located at the periphery of the proximal pars distalis (PPD) and surrounding the pars intermedia (PI). Anti-MyLH, however, also recognized two other cell types, thyrotropin β-immunoreactive (ir) cells and putative follicle-stimulating hormone-like (MyFSH)-producing cells. Labeling of the two latter cell types was prevented by preabsorption of anti-MyLH with M. yellowtail pituitary glycoprotein -subunit. The standard curve for the RIA was generated using purified MyLH, ¹²⁵I-labeled MyLHβ and anti-MyLHβ at a dilution of 1:70,000, which resulted in the binding of 30% of the tracer added. The standard curve ranged from 0.25 to 50 ng/ml. The midrange of the assay (ED50) was obtained with 5.48–7.87 ng LH/ml. The variation between assays was less than 15%. An average cross-reactivity of FSH in the LH RIA of 8.4% was found. Serial dilutions of M. yellowtail pituitary extracts displaced radiolabelled MyLHβ parallel to the MyLH standard. Application of the LH RIA to blood samples and pituitary cell culture medium provided physiological validation of the assay. Significant increases in LH levels were recorded after salmon GnRH treatments in vivo and in vitro. Serum LH levels from wild fish sampled at the spawning season were significantly higher than those from captive fish sampled in the same period.     

Age and growth of the largemouth perch Percichthys colhuapiensis in the Negro river, Argentine Patagonia

Largemouth perch (Percichthys colhuapiensis) represents one of the most economically important fish species in the Argentine Patagonia. However, little research has been done on the age and growth and population dynamics of this fish, though both studies are essential to properly deal with fisheries forecasts and management. As a contribution to elaborating management programmes for P. colhuapiensis, we evaluated the age and growth of this species in the Negro river via scale and whole otolith reading methods. The sample consisted of 579 specimens ranging in total length (TL) from 90 to 475 mm, captured seasonally from December 1994 to December 1995. The formation of scale annuli (end of winter) and the hyaline zone on otoliths (winter) of adult fish coincided with the beginning of the spawning season (end of winter-beginning of spring). The maximum estimated age was 11 years, which indicates that this is a relatively long-lived species. Otoliths were useful for ageing specimens 1–5 years-old, but above this age whole otoliths yielded lower age estimates than scales. Isometric growth of weight with length was found for total population, juveniles, and separate sexes (p > 0.25 in all cases). No significant differences between the length–weight relationships of sexes were observed (p > 0.10). Length at first maturity was significantly higher for males (TL₅₀ = 271 mm TL; r = 0.88) than for females (TL₅₀ = 243 mm TL; r = 0.96) (p < 0.01). Largemouth perch exhibited a consistent pattern of increase in length with age, with a period of fast growth during the first 5 years, and a slow-growing phase during the rest of his life. The growth parameters based on scale data were L∞: 462.1 mm, k = 0.23 and t₀ = −0.94 for total population, L∞: 402.3 mm, k = 0.33 and t₀ = −0.67 for males, and L∞: 548.4 mm, k = 0.15 and t₀ = −1.59 for females, whereas those based on otolith reading were L∞: 537.4 mm, k = 0.17 and t₀ = −1.0 for total population, L∞: 497.6 mm, k = 0.21 and t₀ = −0.79 for males, and L∞: 582.0 mm, k = 0.14 and t₀ = −1.53 for females. Scales are concluded to be the best structure to age P. colhuapiensis because they rendered L∞ values closer to the maximum TL observed, high precision, easiness of collection, low processing time, and the possibility of performing non-destructive monitoring studies.     

Comparison of age estimates from scale, opercular bone, otolith, vertebrae and dorsal fin ray in Labeo rohita (Hamilton), Catla catla (Hamilton) and Channa marulius (Hamilton)

The present study was undertaken with a view to compare the precision and reliability of the age readings obtained from different bony structures of some important freshwater teleosts viz., Labeo rohita (Hamilton), Catla catla (Hamilton) and Channa marulius (Hamilton). Standard procedures were followed to prepare and study the age structures. In L. rohita and C. marulius percent agreement between reader's age estimates was highest for scales, i.e. 96.3% and 90.5%, respectively and in C. catla percent agreement was highest (93.3%) for opercular bone. When scale ages were compared with other alternative structures viz., otoliths, opercular bone, vertebral centra and dorsal fin rays, percent agreement was found highest between scale and opercular bone age estimates (77.8%) in L. rohita and between scale and otoliths (94.8%) in C. marulius. In case of C. catla highest percent agreement was found between opercular bone and scale age estimates. In L. rohita each of the ageing structure showed significant (P < 0.05) underestimation of age in comparison to scales. In C. catla mean age estimates from opercular bone were comparable (P > 0.05) to the values obtained from all other structures except dorsal fin rays. In C. marulius mean age estimates from scales were comparable (P > 0.05) to those from all other structures except from dorsal fin rays. Results indicated scales to be the most suitable structure for ageing L. rohita and C. marulius and opercular bone for C. catla. However, in C. catla also scales may be used as a non-destructive method of age estimation with satisfactory results.     

The utility of otolith weight as a predictor of age in the emperor Lethrinus mahsena and other tropical fish species

This study examines the potential use of otolith weight as a proxy for age in the lethrinid Lethrinus mahsena from different sites in the tropical Indian Ocean: the banks of Seychelles, Mauritius and British Indian Ocean Territory (BIOT, Chagos Archipelago). The reliability of age–frequency distributions and individual ages estimated using otolith weight–age relationships was examined through comparison with those estimated through the standard method of ageing using otolith increments. Two other methods for estimating age–frequencies using age-slicing via an estimated growth curve were also examined; these used growth curves estimated by a length-based method (ELEFAN), or by fitting directly to length-at-age data (an ‘age-based’ method). Age-slicing using length-based growth parameters failed to produce reliable age–frequencies, due to inaccuracies in the growth parameter estimates. The use of age-based growth parameter estimates improved the results of age-slicing, however, age–frequencies remained significantly different from those obtained from ageing using otolith increments in two locations. The use of otolith weight–age relationships resulted in estimated age–frequency distributions that in all locations were not significantly different from those assessed through otolith increment counts. In contrast, L. mahsena otolith weight–age relationships could not be used to estimate individual ages accurately, due to the level of overlap in otolith weight between age classes. Where otolith increments are routinely used to age commercial fish species, the fact that otolith weight–age relationships could not be used to age individuals accurately may limit its application. However, where routine ageing of individuals through otolith increments is considered impractical, for instance because of its cost, the use of otolith weight–age relationships to derive catch age–frequencies represents a viable alternative approach. With this in mind, this study has also demonstrated that there is the potential to use otolith weight–age relationships for five other species caught around the Seychelles, following the validation of their otolith increments.     

Age and growth in southern bluefin tuna, Thunnus maccoyii (Castelnau): Direct estimation from otoliths, scales and vertebrae

In the early 1990s, the spawning biomass of the southern bluefin tuna (SBT) population was estimated to be less than 10% of its historical level. However, major uncertainties surrounding the age composition of the catch confounded the virtual population analysis assessment models. To eliminate these uncertainties, validated estimates of the age composition of the catch were required.We examined scales, caudal vertebrae and sagittal otoliths to determine which structure produced the most accurate age estimates in SBT. Scales proved useful for estimating ages of SBT only up to 4 years. Marginal increment analysis verified that the zones of dense circuli visible on the scales were deposited annually up to this age. In larger fish, the compression of circuli on the margin of scales and high incidence of regenerated scales made estimation of age very difficult. Obvious increments were present on both the vertebrae and otoliths. Age estimates from the two structures matched closely for the first 10 years of life. However, in larger (older) fish the counts diverged, otoliths consistently providing higher age estimates. We determined that annual increments are formed on sagittal otoliths throughout life but that this is not the case in vertebrae, where bands are formed less frequently. Thus, vertebrae were unreliable for estimating age beyond 10 years, which corresponds approximately to the age-at-first maturity.Ages were estimated from otoliths of 1121 fish from throughout the species’ size range. These data indicate that SBT live to at least 40 years of age, twice the longevity previously accepted; that age at recruitment is 1 year, not 2; and that mean age-at-maturity is approximately 11 years, not 7.The age distribution of SBT catches by the Japanese longline fishery in the Tasman Sea indicate that a significant proportion of the SBT population in this area is over 25 years of age and that cohorts spawned in the late 1970s and early 1980s are markedly under-represented in the population. The latter is thought to result from intense exploitation on these cohorts by the Australian surface fishery soon after recruitment.     

黄鳍棘鲷家系亲缘关系鉴定

为了建立黄鳍棘鲷微卫星亲子鉴定技术,利用荧光引物和自动测序技术检测了自主开发的12对微卫星分子标记在505尾黄鳍棘鲷个体中的遗传多态性,并构建了亲子鉴定技术。结果显示,该研究中筛选的12个微卫星标记共检测到119个等位基因,平均等位基因数(N_a)为9.91,平均观测杂合度(H_o)为0.651,平均期望杂合度(H_e)为0.661,平均多态性信息含量(PIC)为0.621,具有丰富的多态性。此外,运用Cervus 3.0软件对已知系谱信息的112尾黄鳍棘鲷亲本和393尾子代个体进行模拟分析,结果显示,当双亲未知且置信度为95%时,12个标记的累积排除概率达99.58%;当微卫星标记数量为8时,累积排除概率达到99.1%。因此确定AL49、AL37、AL01、AL20、AL14、AL18、AL15和AL51共8个多态性较高的微卫星标记为黄鳍棘鲷微卫星亲子鉴定的核心体系。在双亲性别未知的情况下,其双亲的累积排除率为99.1%。根据黄鳍棘鲷子代的实际基因分型数据,实际鉴定率为89.31%。该研究构建的微卫星标记组合能为黄鳍棘鲷不同...     

Breeding and juvenile culture of the lined seahorse, Hippocampus erectus Perry, 1810

All seahorse species worldwide have been placed under CITES Appendix II since 2004, because they have been over-exploited for traditional Chinese medicine and aquarium trades. Aquaculture has been recognized as a long-term solution for sustaining the seahorse trade while minimizing wild collection. In this study, we evaluated the breeding and juvenile culture of an important aquarium seahorse species, the lined seahorse Hippocampus erectus, Perry 1810. Pairing, mating and copulation behavior were observed. Gestation time and brood size were 17.33 ± 2.94 days and 272.33 ± 66.45 individuals/brood, respectively. Growth rates differed among juveniles from different broods. Effects of temperature on the growth rates and survivorship of the juveniles during the first two weeks were compared. The highest growth rate and survivorship of the juveniles occurred at 28–29 °C among the temperatures tested (24–33 °C). Growth rate and survivorship of the juveniles during the first 9 weeks at 28 °C were investigated. The final standard length and survivorship of the juveniles were 6.32 ± 0.52 cm and 71.11 ± 10.18%, respectively, and the relationship between the wet weight and the standard length of the juvenile seahorses can be expressed as: W = 0.0034 L^2.5535 (r² = 0.9903, n = 12, P < 0.01). These findings suggest that H. erectus is a good candidate for commercial aquaculture.     

Geographic influences on and the accuracy and precision of age estimates for the red bass, Lutjanus bohar (Forsskal 1775): A large tropical reef fish

The red bass is a large tropical reef fish (Lutjanidae, tropical snappers) that is harvested to varying extents throughout a widespread Indo-Pacific distribution. The aims of this study were to investigate the accuracy and precision of age estimates from transverse sections of sagittal otoliths and to assess effects on these of the geographic area of collection and otolith preparation method. Two independent validation studies suggested an approximately annual formation of annuli in otoliths, predominantly for otoliths with 4–10 annuli but also for one otolith with 29 annuli. Otolith sections produced exceptionally high annulus counts: up to 56 annuli for samples from the Great Barrier Reef (GBR), Australia; and up to 55 annuli from the Seychelles, indicating a high longevity for this species. The precision of otolith readings from the GBR (index of average percent error, IAPE = 3.21 ± 0.26 S.E.) was within commonly accepted bounds for age estimation (IAPE up to 5%) but precision of readings from the Seychelles was significantly lower (IAPE = 9.18 ± 0.47 S.E.) and outside of this “acceptable” range. Age-based biological parameters for red bass from the Seychelles should thus be applied with greater caution than those for red bass from the GBR. If basic demographic properties are assumed relatively constant across the wide geographic range sampled, however, results from the GBR could be used as more reliable preliminary data for precautionary management strategies in the Seychelles and elsewhere.     

Larval group differentiation in Atlantic cod (Gadus morhua) inside and outside the Gullmar Fjord

The spatial and temporal occurrence of pelagic fish stages and their biological variability may affect their dispersal and survival, and ultimately fish recruitment. We collected Atlantic cod larvae at one station inside and at one station outside the Gullmar Fjord, eastern Skagerrak, in order to investigate small-scale larval group differentiation. Rectangular midwater trawl hauls were taken every 6 h (during 24 h) from three separate depth intervals between the surface and 70 m depth. About 80% and 20% of all larvae occurred above the halocline at the Fjord station and the Coastal station, respectively. Hatching (at both stations) occurred from the 3rd week in February to the 1st week in May, indicating that cod larvae were present for at least 5 months (from late February to early August). The length and hatch date frequency distributions of larvae from the surface layer were unimodal inside the fjord but bimodal outside the fjord. Analyses of seven microsatellite DNA loci indicated that larvae collected inside the fjord (where local spawning occurs) were genetically distinct from larvae sampled on the outside (F_ST = 0.0026). The two age cohorts outside the fjord were not, however, genetically different, nor were larvae collected at different depths. We conclude that small-scale variability of vertical concentration and larval life history variability should have consequences for interpreting models of larval dispersal and survival, and subpopulation structure analyses.     

Annual sex hormonal profiles, gonad development and age determination of the Mekong giant catfish (Pangasianodon gigas, Chevey)

Annual sex hormonal profiles, gonad development and age determination of 18 (13–14 kg body weight) and three (145–226 kg body weight) Mekong giant catfish (MGC) (Pangasianodon gigas, Chevey) reared in earthen ponds in Chiang Mai and from the Mekong River in Chiang Rai, Thailand, respectively, were investigated. The hormonal profiles were determined from blood samples of the fish by electrochemiluminescence immunoassay during May to August in 2000. The highest testosterone levels of 0.06 ng mL^?1 in both sexes and the highest oestradiol of 47.8 and 14.23 pg mL^?1 in females and males, respectively, were observed in May. The gonadosomatic index was found to be 0.07 for males and 0.38 for females from ponds in comparison with 2.27 for males and 8.29 for females from the Mekong River. Higher development stages of spermatocytes and oocytes of the cultured fish in May than in February and November were demonstrated. No mature germ cells were obtained from either the males or females, indicating no sexual maturity. The average age of fish was determined from the annual rings of the cross‐section of the pectoral fins by a stereomicroscope. The average age of fish in earthen pond determined from the annual ring was 8 years, which agreed with the actual culture records, while those from the Mekong River were 21 years. This information will be beneficial for the breeding programmes and conservation of the MGC.     

Inclusion of blue mussel extract in diets based on fish and soybean meals for tiger puffer Takifugu rubripes

Inclusion of the water-soluble fraction of blue mussels Mytilus galloprovincialis as a feed additive was examined with tiger puffer Takifugu rupbripes. The control diet mainly consisted of fish meal, potato starch, and pollack liver oil. Experimental diets were formulated to replace 30% and 40% of the fish meal protein with defatted soybean meal (SBM), and were supplemented with 0–20% mussel extracts. Fish of 18 g initial body weight were fed each diet to satiation, twice daily, 6 days per week for 7 weeks at 20°C. Weight gain and protein efficiency ratio of fish fed the diet containing SBM without the extract were significantly lower than those of the control at the 30% replacement level. Addition of 5% or 10% extract improved the growth and feed utilization to levels comparable to those of the control. At 40% substitution, statistically identical growth and feed performance to the control were obtained for diets supplemented with 10% or 20% extract; however, performance for 5% addition was significantly lower. Thus, the water-soluble fraction of blue mussels would be an effective feeding stimulant in aquaculture feed for tiger puffer that makes it possible to replace 30–40% of fish meal protein with SBM.     

东海剑尖枪乌贼生物学特征

文章根据2017年和2018年9月至翌年3月在东海采集的剑尖枪乌贼 (Uroteuthis edulis) 样本,对其耳石形态进行观察与测量,并结合日龄信息对耳石微结构及生长特征进行了研究。结果表明,耳石生长纹由明暗相间的环纹组成,依据生长纹的宽度及亮度划分为后核心区、暗区和外围区。通过耳石日龄进行逆推发现春、夏产卵群体为优势群体,优势群体间耳石各形态参数差异显著 (P<0.05)。主成分分析表明,耳石总长 (TSL) 和最大宽度 (MW) 可作为表征春、夏产卵群体耳石长度和宽度的指标。春、夏产卵群体TSL生长模型采样年间差异均显著 (P<0.05),春季产卵群体分别以逻辑斯蒂和对数生长模型拟合最佳,夏季产卵群体以逻辑斯蒂和线性拟合最佳。春、夏产卵群体MW生长模型采样年间差异均不显著 (P>0.05),以逻辑斯蒂生长模型拟合最佳,性别间差异不显著 (P>0.05)。180~240 d,春季产卵群体TSL和MW的生长速率均大于夏季产卵群体。

     

闽南—台湾浅滩渔场中国枪乌贼生物学特性研究

头足类是最具开发潜力的渔业种群之一,然而其资源易受环境变化影响,复杂的交互作用致使二者空间关系呈现非均一性。中国枪乌贼 (Uroteuthis chinensis) 是南海北部近海重要的经济物种,且在渔业群落结构中占据优势种地位,故正确理解与掌握该物种资源-环境关系的空间特征,有助于该资源的保护与利用。基于南海北部近海2014年夏季的渔业资源调查数据,构建了地理权重回归模型 (Geographical weighted regression, GWR),探索该海域中国枪乌贼的资源分布与海洋环境关系的空间特征,阐述主要影响因子。模型评价指标结果表明,GWR的最小赤池信息准则 (Akaike Information Criterion, AIC) 和校正决定系数 (Adjusted R-Squared, 相似文献   

Age, growth and reproductive biology of the European conger eel (Conger conger) from the Atlantic Iberian waters

The European conger eel, Conger conger, is a fish widely distributed in the north-eastern Atlantic, being an important commercial and recreational fish species. A total of 85 juvenile congers eels were used in this study. Seventy-three congers were captured mainly by hook and pots in inshore waters (10–15 m depth) of the Iberian Peninsula (North Portugal and Vigo), monthly from March 1998 to March 2000. Another twelve specimens have been captured during a research cruise (R.V. “Capricórnio”) in summer 1999 by trawl at depths about 400 m in south Portugal. The length and weight of the congers eels ranged from 38 to 173 cm and 125 to 14,553 g, respectively. The observation of burnt otoliths under UV light proved to be a useful method for ageing conger eels. Marginal increment analysis was used to validate the annual pattern in the deposition of bright zones in the otoliths. Age for the congers ranged from 2 to 12 years. The VBF population growth curve estimates from the otoliths of the females gave results of L_∞ = 265 cm, k = 0.07 and t₀ = −1.20. Sex determination and gonadal development were obtained from histological analysis. All the specimens collected in the coastal shallow waters were females, either immature or in a developing stage. The ovaries contained oocytes in two main stages of development: a pre-vitellogenic stage and an early vitellogenic stage. The few males (n = 4) observed have been captured in the trawl fishery at deeper waters. The males possessed small cells spermatogonias and spermatocytes clustered in crypts in the testis scattered in a matrix of adipose tissue. The sexual steroids, 17β-oestradiol and testosterone, were measured in blood plasma samples by solid-phase radioimmunoassay. Both sexual steroids presented a high correlation with the sexual development stage in terms of maximum oocyte diameter and gonadosomatic index. This work presents for the first time, data on age, reproductive biology and endocrinology of conger eels captured in the west coast of the Iberian Peninsula.     

Comparison between surface-reading and cross-section methods using sagittal otolith for age determination of the marbled sole <Emphasis Type="Italic">Pseudopleuronectes yokohamae</Emphasis>

To find an appropriate method for age determination in the marbled sole Pseudopleuronectes yokohamae in Tokyo Bay, Japan, sagittal otoliths of 1,343 individuals were observed by surface-reading and cross-section methods and the results were compared. Opaque zones occurred once a year and were regarded as annuli in both methods. The surface-reading method sometimes provided a lower count of the number of annuli than the cross-section method, and the frequency of this discrepancy was highest in older fish (males above 5 years, females above 4 years). The oldest female fish was estimated to be age 10 years by the cross-section method but 8 years by the surface-reading method. The cross-section method could provide a more accurate estimate of age and is therefore likely to be indispensable to estimations of longevity. In contrast, the surface-reading method is superior in terms of cost and time efficiency but is likely to underestimate the ages of older fish. However, growth equations based on age estimated by the surface-reading method were sufficiently accurate if males ≥5 years and females ≥4 years were combined as specific, single age groups of 5+ and 4+, respectively.