Age determination in the Antarctic shrimp Notocrangon antarcticus (Crustacea: Decapoda), using the autofluorescent pigment lipofuscin

Determination of basic population parameters in long-lived Crustacea is hindered by a lack of appropriate methods for age determination. This study uses the pigment lipofuscin as an age marker in the common Antarctic decapod Notocrangon antarcticus (Pfeffer, 1887) from the eastern Weddell Sea. Resin brain sections of the lateral somacluster of the olfactory lobe of 189 specimens were digitally recorded by confocal microscopy and images were subsequently analyzed. A modal progression analysis of the lipofuscin concentration–frequency distribution revealed a total of eight regularly spaced modes presumed to reflect consecutive annual age classes. All eight modes contained females, and the first four contained males. No regular modes were obvious in the comparable length-frequency distribution. The average yearly pigment accumulation was nearly linear and estimated as 0.02% area fraction year⁻¹, which is considerably lower than rates published for species from lower latitudes. This is probably explained by the effect of low water temperature on metabolism and lipofuscin accumulation rate. The growth parameters CL_∞ and k from the von Bertalanffy growth function were 22.3 mm and 0.79 year⁻¹ for females, respectively, and 16.9 mm and 0.64 year⁻¹ for males, respectively. Mortality, estimated from catch curves, amounted to 0.44 year⁻¹ in females and 0.92 year⁻¹ in males, whereas P/B, calculated from the mass specific growth rate method, was slightly lower. The results indicate that the lipofuscin-inferred population parameters are an improvement over what can be learned about N. antarcticus with traditional methods. Received: 1 August 2000 / Accepted: 21 September 2000     

Population structure, growth and recruitment of the euryalinid brittle-star Astrobrachion constrictum (Echinodermata: Ophiuroidea) in Doubtful Sound, Fiordland, New Zealand

The euryalinid brittle-star (snake star) Astrobrachion constrictum (Farquhar) lives coiled around the branches of black coral (Antipathes fiordensis) colonies. Twenty-two vertical transects, 10 m wide by 30 m deep, were swum in Doubtful Sound over a 2.5 yr period from 1993 to 1995. Numbers, disc diameters and colour morphotypes of brittle-stars inhabiting coral colonies were recorded. 36.3% of the coral colonies >200 mm tall (n = 292) hosted ≥1 Astrobrachion constrictum (range 0 to 12). Overall, the population was patchily distributed on the available coral habitat. The dark red colour morphotype of A. constrictum was most common (87%, n = 279) followed by the yellow, striped, and then spotted varieties. The population was comprised mainly of large (≥10 mm disc diam) individuals, and juveniles were rarely encountered, indicating low rates of recruitment or a high mortality of recruits. Disc-diameter data gathered from this and previous studies indicated that growth in A. constrictum is initially rapid, with individuals reaching a disc diameter of 15 mm in ≃2.5 yr; growth decreases with age, as in other deep-sea ophiuroids. Growth rate within years, however, was not constant, with faster growth in the spring/summer. Maximum size for A. constrictum is reached in ≃8 yr at ˜23 mm disc diam. Anecdotal evidence indicates that A. constrictum may not be confined solely to black coral colonies. Received: 25 September 1996 / Accepted: 16 October 1996     

Validation of daily increment deposition in otoliths. Age and growth determination of Aphia minuta (Pisces: Gobiidae) from the northwest Mediterranean

The transparent goby Aphia minuta (Risso, 1810) is one of the main target species of the small-scale fishery off the Island of Majorca. Otolith microstructure and length-frequency analysis were used to study the age and growth of this species during the 1982/1983 and 1992/1993 fishing seasons. Daily periodicity of increment formation was determined by experiments with marked otoliths in individuals maintained in captivity. The length range of the catches during the 11 yr period was between 12 and 49 mm, with a main distribution (89%) between 24 and 40 mm. Otolith age-readings indicate that the population exploited in the commercial fishery consists of seven age-groups (2 to 8 mo old), with a very high proportion of individuals (95%) between 3 and 6 mo old. Population growth-curves revealed no differences between males and females. The growth parameters for the whole population are: asymptotic length, L _∞ = 53.69 mm; growth coefficient, K = 2.23 yr⁻¹; theoretical age at length zero, t ₀ = −0.005 yr. Those individuals of A. minuta caught in Majorca during the winter period reached a maximum age of 7 or 8 mo. Received: 30 December 1996 / Accepted: 16 April 1997     

Age and growth of the mesopelagic squid Ancistrocheirus lesueurii (Oegopsida: Ancistrocheiridae) from the central-east Atlantic based on statolith microstructure

Statolith microstructure was studied in 56 Ancistrocheirus lesueurii (25 to 423 mm of mantle length, ML) caught in the central-east Atlantic. Statolith growth increments were grouped into three main growth zones, distinguished mainly by increment width. The second transition in the statolith microstructure (from Zone 2 to Zone 3) coincides with the life history shift from epipelagic and upper mesopelagic to a bathyal habitat. Second-order bands (mean 27.65 growth increments) and sub-bands (mean 13.6 growth increments) within statolith microstructure appeared to be related to the lunar cycle. Striking sexual dimorphism is reflected in the age and growth rates: males live ca. 1 yr, while females only start maturing at this age and obviously live >1.5 yr. A. lesueurii is a slow growing squid, attaining 25 to 30 mm ML at the age of 100 d. After ontogenetic migrations into bathypelagic waters at ML > 30 to 35 mm, growth rates gradually decrease to the minimum known values for squids. Based on back-calculated hatching dates, A. lesueurii hatches throughout the year with a peak between November and March. Received: 28 August 1996 / Accepted: 31 January 1997     

The influence of ration level on growth and statolith increment width of the tropical squid Sepioteuthis lessoniana (Cephalopoda: Loliginidae): an experimental approach

Juvenile squids were grown in individual 2.6-l floating enclosures and were fed either a high- or a low-ration diet of fish and the crustacean Acetes. Squids were maintained for a maximum of 44 days in two experiments. The high-ration individuals reached a significantly larger size in both experiments (27, 25.5 mm mean mantle length, ML) compared to their low-ration siblings (19 mm mean ML) in both experiments. The statolith increment widths prior to the start of the experiment were significantly wider (between 3 and 4 μm) compared to the increment widths after the start of the experiment (between 2 and 3 μm) both for the low- and the high-ration squids. High-ration squids also had significantly wider increments and larger statoliths than their low-ration siblings. Even though we detected consistent trends in daily statolith increment widths for the different feeding regimes, we could not detect variation in increment widths at a daily level of resolution (i.e. as a result of differences in day-to-day food intake at an individual level). This was probably due to the relatively consistent diet experienced by each individual. These experiments revealed that ration level influences squid growth rate, statolith size and daily statolith increment width. Received: 30 March 2000 / Accepted: 30 October 2000     

Female choice in the opportunistic mating of wild chimpanzees (Pan troglodytes schweinfurthii) at Mahale

For female chimpanzees (Pan troglodytes schweinfurthii) in the Mahale Mountains National Park, Tanzania, the most common mating pattern is opportunistic. In such opportunistic matings, females copulated promiscuously but not randomly. This study describes female mate choice during 1-year observation of six females who exhibited regular genital-swelling cycles. During the study period, 169 opportunistic matings and four restrictive matings were recorded over the course of 51 days. As female estrus progressed, mating frequency and the number of adult male mating partners increased, although the number of potential mating partners did not change. Criteria of female choice examined were the direction and consent/rejection of courtship, proximity maintenance, and female grooming. Adult-male courtships were successful more often than those of adolescent males. During the earlier phase of estrus, females copulated rather promiscuously with many males. But during the later phase of estrus when the likelihood of conception is expected to be highest, they copulated repeatedly with high-ranking adult males. There was a positive correlation between female grooming frequency and mating frequency when the likelihood of conception was greatest. Female chimpanzees are thought to choose high-ranking males as fathers of their offspring. Moreover, female chimpanzees may adopt one or both of two mating strategies, i.e., a many-male strategy and a best-male strategy. Received: 23 November 1998 / Received in revised form: 12 April 1999 / Accepted: 26 April 1999     

Development, maturation, brood size and generation length of the mesopelagic amphipod Cyphocaris challengeri (Gammaridea: Lysianassidae) off southwest Hokkaido, Japan

 Using the number of segments of pleopod rami as a marker of instar number, the population structure (instar composition) of the mesopelagic gammarid amphipod Cyphocaris challengeri was investigated by monthly samplings from May 1997 to April 1999 at a station off southwest Hokkaido, Japan. Laboratory-rearing experiments were also conducted to establish the relationship between the number of segments of pleopod rami and instar number, and to estimate the growth pattern of this gammarid based on the intermolt period and molt-increment data. Stratified sampling in the field (0 to 200 and 200 to 400 m depth strata) showed this species occurred mainly at 200 to 400 m depth during the day. Instar analysis indicated that C. challengeri has 12 instars in females and 11 instars in males. Based on observations of secondary sexual characters, Instars 1 to 6 were designated juveniles (Instars 1 to 3 occurred in the marsupia of gravid females); in males, 7 to 9 were immature and 10 and 11 were mature, while in females 7 and 8 were immature and 9 to 12 were mature. Off southwest Hokkaido, Instar 4 (just released from a female's marsupium) was found throughout the year, with a peak abundance occurring in April to July of each year. A sequential development of Instar 4 to 9 (youngest adult instar) through the year was observed. Generation length (i.e. the time required to grow from Instar 4 to 10) was estimated from a laboratory-obtained growth curve to be 216 to 584 d at the in situ temperature range (2 to 5 °C), which is consistent with observations on field populations. Specimens older than Instar 9 were rare in the field and could not be used in laboratory-rearing experiments, so longevity could not be estimated. Eggs were oval and measured 0.6 mm (large diameter). Brood size ranged from 20 to 65. Comparing the present results with those of epipelagic hyperiid amphipods, the nearly identical growth rates together with the production of fewer but larger eggs seen in C. challengeri appear to reflect to the typical life mode of deep-living pelagic crustaceans. Received: 14 February 2000 / Accepted: 6 July 2000     

Social monogamy and the threat of infanticide in larger mammals

The evolution of social monogamy in larger mammals is difficult to explain because males usually do not invest much in direct offspring care and might achieve greater fitness by deserting a pregnant female to reproduce with additional females elsewhere. It has been hypothesized that socially monogamous males remain with the female year-round to protect their offspring from infanticide by new immigrant males. We investigated this idea by analyzing all cases of infant loss in a wild population of white-handed gibbons (Hylobates lar; Primates), in which most groups were socially monogamous and some polyandrous (137.5 group years). We examined the influence of (a) male intruder pressure on male immigration rates and (b) the presence of a new male in the group on infant loss. We found no relation between intruder pressure and male immigration rates. Infant loss was lowest (4.5%) for stable monogamy (probable father stayed from conception through infancy) and intermediate (25.0%; p = 0.166) for stable polyandry. If a new male immigrated after conception, however, the infant was lost in all cases (p < 0.01) independent of the presumed father’s presence. Overall, 83.3% of infant losses were associated with the presence of a presumably unrelated male. Although the sample size is small, our results provide the first true support for the idea that the risk of infanticide is an important factor in the evolution of social monogamy in larger mammals.     

Fecundity and spawning in a deep-water cirromorph octopus

 Reproductive characteristics of cirromorph octopuses, assigned to the species Opisthoteuthis grimaldii, were sampled as a commercial fishing by-catch on the Hebrides Slope, west of Scotland. A total of 254 specimens (99 female, 155 males), retrieved from bottom trawls fished at 750 to 1500 m depth, were examined. A maximum of 2097 eggs was counted in a single female ovary (mean female body weight 1242.8 g), most of them <1 mm in length. At egg lengths over 1 mm, diminishing numbers of eggs were present in 1 mm size categories up to a maximum of ≈10 mm. At body sizes >500 g (wet wt), and in every female >750 g (max. female weight recorded in the sample was 2959 g), a succession of unattached eggs was present in the proximal oviduct and a single, unattached mature egg occupied the tip of the distal oviduct. These females were assumed to be in spawning condition and the characteristics of egg distribution in the reproductive tract to be consistent with sequential release of individual eggs and continuous spawning throughout the growth period and lifespan of the mature octopus. In pre-spawning females there was a positive relationship between estimated egg numbers and maximum egg size. After the onset of spawning there was no significant further increase in estimated potential fecundity over the body-size range 500 to 3000 g. Follicular sheaths remaining in the ovary after release of eggs into the proximal oviduct were counted and used to estimate the total number of eggs released up to the time of capture. Follicular sheaths first appeared at 500 to 650 g body weight and increased steeply in number to >1000 in females >1500 g. Two individuals were found with ovarian follicular sheaths but with no terminal egg in the distal oviduct; these were assumed to have released their egg just before capture. Summation of the number of follicular sheaths counted plus the number of eggs estimated as remaining attached in the ovisac, provided a revised estimate of total potential fecundity and raised the estimate for any individual to a maximum of 3202 eggs (mean = 1396 eggs). Received: 3 February 2000 / Accepted: 17 May 2000     

Offspring sex ratio variation in the bridled nailtail wallaby, Onychogalea fraenata

The bridled nailtail wallaby is a sexually size dimorphic, promiscuous, solitary macropod. Sex ratios of pouch young were studied at two sites over 3 years, beginning with 14 months of severe drought. Females that were in better condition were more likely to have sons, and condition was dependent on body size. Females at one site were heavier, were consequently in better condition, and produced more sons than females at the other site. Females that declined in condition had more daughters during the most severe part of the drought than females that maintained condition, but endoparasite infection did not affect the pouch young sex ratio. Age also appeared to affect sex ratio adjustment, because weight was strongly influenced by age. Sex ratio bias was not caused by early offspring mortality, but occurred at conception. Mothers did not appear to bias energy expenditure on sons or daughters; males and females did not differ in condition at the end of pouch life. Pouch young sex ratio variation was most consistent with the Trivers-Willard hypothesis, but could also have been influenced by local resource competition, since sons dispersed further than daughters. Offspring condition was related to survival, and was correlated with maternal condition. Received: 14 April 1998 / Accepted after revision: 10 November 1998     

Life under Arctic sea ice – reproduction strategies of two sympagic (ice-associated) amphipod species, Gammarus wilkitzkii and Apherusa glacialis

The reproductive strategies of two gammaridean amphipod species, Gammarus wilkitzkii and Apherusa glacialis, that permanently inhabit the Arctic sea ice were investigated. G. wilkitzkii reaches sexual maturity at an age of 2 years and produces 128 ± 54 eggs fem.⁻¹ yr⁻¹. Mating takes place during fall and winter, and the development of the large eggs (0.60 to 0.80 mm diam.) lasts 6 to 7 months. The sex ratio of G. wilkitzkii was dominated by males in a proportion of 1.5:1. In vivo studies showed that juveniles are released in batches from the brood pouches of the females during April and May. A. glacialis reaches sexual maturity at the age of 1 year and produces 555 ± 151 eggs fem.⁻¹ yr⁻¹. The eggs are between 0.18 and 0.23 mm in diameter, and are the smallest known for gammaridean amphipods. Eggs are kept in packages of two to eight in the brood pouches of females. The sex ratio of A. glacialis was dominated by females in a proportion of 3:1. The high fecundity of both amphipod species, the release of juveniles in batches over a period of time, a high proportion of females (A. glacialis), and an elongated life-span with multiple spawnings (G. wilkitzkii) are discussed as possible adaptations to the specific and highly variable conditions under Arctic sea ice. Received: 29 December 1999 / Accepted: 8 March 2000     

Male takeover,infanticide, and female countertactics in white-headed leaf monkeys (<Emphasis Type="Italic">Trachypithecus leucocephalus</Emphasis>)

Infanticide by males is common in mammalian species such as primates in which lactation lasts much longer than gestation. It frequently occurs in one-male groups following male takeovers and is likely a male reproductive strategy. Reported female countertactics include abrupt weaning of infants, dispersal, or paternity confusion. Here, we estimated costs of female countertactics in terms of weaning ages and interbirth intervals. We observed a population of white-headed leaf monkeys (Trachypithecus leucocephalus) in Nongguan Nature Reserve, China (1995–2006) mainly composed of one-male groups. Takeovers (N = 11) coincided with the peak conception period. Detailed data are presented for five takeovers (34 females, 29 infants, and 47 group-years) leading to six infant disappearances (42.9% of infant mortality). All presumed infanticides were in accordance with the sexual selection hypothesis. Following a takeover, females without infants or with old infants stayed with the new males, incurring no or low costs (via abrupt weaning). Females with young infants dispersing with the old males also experienced low costs. High costs (due to infant loss) were incurred by pregnant females and those with young infants who stayed with the new males indicating that paternity was not confused. Costs in terms of long interbirth intervals were also high for females leaving with the old males to later join the new males, despite infant survival. Female countertactics reflected female philopatry mediated by infant age. Presumably due to the seasonal timing of takeovers, most countertactics seemed successful given that 32.3% of females apparently incurred no costs and 41.2% incurred only low costs.     

Early life history and recruitment of the tropical eel Anguilla bicolor pacifica, as revealed by otolith microstructure and microchemistry

Otolith microstructure and microchemistry of the tropical eel Anguilla bicolor pacifica Schmidt were examined in glass eels collected at the mouth of the Dumoga River, North Sulawesi Island, Indonesia. Ages of the glass eels examined (age at recruitment) ranged from 124 to 202 d (167 ± 19.3 d; mean ± SD), hatching being estimated as having occurred between November 1995 and March 1996. Otolith increment widths markedly increased from age 101 to 172 d (135 ± 18.2 d; mean ± SD), coincident with a drastic decrease in otolith Sr:Ca ratios, suggesting that metamorphosis began during that period. The duration of metamorphosis was estimated as 20 to 40 d, on the basis of otolith microstructural characteristics. The fluctuation patterns in otolith increment widths and Sr:Ca ratios were similar to those of the temperate Japanese eel A. japonica. Received: 20 May 1998 / Accepted: 7 October 1998     

Strontium/Calcium ratios in statoliths of the neon flying squid, Ommastrephes bartrami (Cephalopoda), in the North Pacific Ocean

Strontium to calcium ratios were observed along longitudinal sections of statoliths of nine neon flying squid, Ommastrephes bartrami (LeSueur, 1821), including three mature females (422 to 454 mm mantle length, ML; 207 to 306 d old) obtained from the North Pacific (27–35°N; 144–150°E) during winter and six immature males and females (187 to 226 mm ML; 126 to 164 d old) collected from 39°N; 145°E and 39°N; 169°W during summer. The distances between the nucleus (core) and the edge of the dorsal dome were approximately 660 to 690 μm in mature females and 450 to 510 μm in the immature squid. Sr/Ca ratios were determined at intervals of 30 μm between the nucleus and edge of the dorsal dome. Sr/Ca ratios were higher in areas near the nuclei and peripheral portions of the dorsal dome than in the middle portions of the statoliths (270 to 420 μm from the nuclei, corresponding to ages of 60 to 90 d) in mature females; thus a U-shaped pattern was evident. Sr/Ca ratios in the six immature squid decreased from nucleus to the dorsal dome; in three squid the ratios slightly increased toward the dorsal dome edge. The observed Sr/Ca ratios in immature squid were considered to represent younger portions of the U-shaped pattern. In the present study we discuss this pattern in relation to environmental and biological conditions of O. bartrami, which undertakes seasonal migrations between spawning grounds in the Subtropical Domain and feeding grounds in the Subarctic Domain and Transitional Zone in the North Pacific Ocean. Although Sr/Ca ratios are potentially affected by ambient water temperature and ontogenetic conditions, including somatic growth and statolith growth, it was impossible to evaluate each environmental and biological effect separately, as variations in these factors are complicated and effects could be interdependent. Received: 11 April 1997 / Accepted: 27 December 1997     

An estimate of female mate searching costs in the lekking butterfly Coenonympha pamphilus

We estimated the cost to females of the lekking butterfly Coenonympha pamphilus of visiting males on leks instead of taking off and soliciting courtship from males passing them outside leks, as occurs in the non-lekking congener C. tullia. We followed released virgin females of C. pamphilus in the field until they mated. We estimated the time they lost by remaining perched and not approaching males that passed them, and observed how often and at what distance virgin females were passed by males in the field. We then calculated how much faster these females would have been detected if they had taken off and approached these males, using probabilities of detection as a function of passing distance derived from field observations on C. tullia females. C. pamphilus females on average lost 201 min by not approaching males on their way to leks. To estimate what this time loss meant in terms of fitness, we measured how the age at mating affected fecundity. Using field measures of fecundity and mortality, the time loss translated into an average 2.8% reduction in fecundity as a best estimate, and an average 1.3% reduction in fecundity as a lower estimate. This fitness cost is larger than has been reported earlier for a lekking bird, but is probably too small to eliminate the possibility of indirect benefits of mating with males on leks. Received: 15 August 1996 / Accepted after revision: 24 January 1997     

Age and growth of Electrona antarctica (Pisces: Myctophidae), the dominant mesopelagic fish of the Southern Ocean

Numerically and in biomass, the lanternfish Electrona antarctica is the dominant fish in the vast pelagic region of the Southern Ocean bounded on the north by the Antarctic Convergence and in the south by the Antarctic continental shelf. It is an important krill predator, and in turn is important in the diets of flighted and swimming seabirds. Further, it is the southernmost and coldest-dwelling representative of the globally distributed fish family Myctophidae. The present study was undertaken to estimate the species' growth rate and average life span, to incorporate the information in a basic energy budget, and to compare the growth of E. antarctica with more northerly confamilials. Fishes were aged using primary growth increments that were resolved on sagittal otoliths using three sequential techniques: thin-section grinding and polishing, etching, and scanning electron microscopy (SEM). Based on increment width (0.8 to 1.2 μm), continuity, and previous studies on confamilials, the microincrements were assumed to be deposited on a daily basis. Montages of SEM photomicrographs were constructed for each sagitta to allow the daily rings to be counted over the entire life span of 31 individuals representing the entire size range of the species. Results suggest a larval stage of 30 to 47 d and a maximum life span of 3.5 yr, with females growing faster than males in the last 1.5 yr of life and reaching a larger maximum size. Construction of a simple energy budget using the best information available suggests that a surplus of energy is available to support the observed growth rates (0.05 to 0.07 mm d⁻¹). The results of the present study contrast markedly with previous estimates of an 8 to 11 yr maximum age for E. antarctica. These results provide important data addressing the ecology and population dynamics of the pelagic Antarctic ecosystem. E. antarctica is the end-member species in the continuum of vertically migrating myctophids that extend from the equator to the polar circle. Its growth rate is consonant with that of all other myctophid species examined using primary growth increments to determine age. The present study, in conjunction with earlier studies, suggests that growth rates of mesopelagic species are far higher than previously thought. Received: 12 September 1997 / Accepted: 25 July 1998     

Influence of temperature on the microstructure of statoliths of the thumbstall squid Lolliguncula brevis

 A laboratory study investigating the influence of temperature on the microstructure of statoliths of Lolliguncula brevis is described. Groups of squid were subjected to various temperature regimes for periods in excess of 30 d. Statoliths extracted from 20 squid were examined using a confocal microscope in laser scanning mode. The parts of the statoliths deposited during the course of the experiments were identified using either putative daily increment counts or from checks produced in response to capture and handling. These checks appear to consist of a series of prominent increments rather than reflecting a period of interrupted statolith growth. Increments deposited during the experiment generally displayed reduced contrast and clarity in comparison to the “wild” parts of the statolith, presumably in response to the constant conditions imposed in the laboratory. Average statolith growth rates observed over the course of the experiment showed a strong positive relationship to ambient temperature. A significant sex effect was apparent, with statoliths of female squid generally growing faster than those of males. Observed statolith growth rates at 15 °C were generally below 1 μm d⁻¹, suggesting that the widths of daily increments produced under these conditions may approach the resolution limits of a light microscope. The implications for studies using increment numbers to estimate age are discussed. Received: 23 July 1999 / Accepted: 17 February 2000     

Studies on the growth,reproduction, and life cycle of the supralittoral isopod Ligia pallasii

A two-year study on a field population of Ligia pallasii Brandt has shown that the isopods live for 1.5 to 2 years. Breeding occurs in the spring and early summer, with some females carrying winter broods of eggs. The mean length of breeding females is 22.5±2.2 mm (standard deviation) and the mean brood size is 48±11 eggs. Mature males are larger than mature females (900 and 300 mg live weight, respectively), and are disproportionately broader (31×17 mm and 22.5×9 mm, respectively). The larger size and breadth of the males is an adaptation for copulation, and may be atributed in some measure to slower growth of the female due to the extra energy demands of reproduction. The overall 1:1 ratio of males to females in the population represents the balance between an equal sex ratio in the immature stages, more females in the 18 to 24 mm length category, and more males in the larger length categories. This condition is attributed mainly to the faster growth of the males.     

Sexual maturity and hermaphroditism of the red porgy Pagrus pagrus (Teleostei: Sparidae)

Gonadal changes related to sexual maturity were examined by histology in reared populations of the red porgy Pagrus pagrus L., aged 0.5 to 6.5 years. More than 50% of red porgies were mature at the age of 4 years although some individuals were already mature at the age of 3, as indicated by changes in the gonadosomatic index, plasma levels of vitellogenin, 17β-estradiol and testosterone in females and males. Sex frequency distribution analysis in relation to the age and histological analysis of the gonads indicated the presence of males originated from the sex change of adult functional females. P. pagrus is a protogynous species. Some females had not changed sex up to the age of 6.5 years. Received: 16 July 1998 / Accepted: 29 April 1999