Changes In Gonadosomatic Index Research Articles

Laboratory Spawning Patterns of Mummichogs,Fundulus heteroclitus(Cyprinodontiformes: Fundulidae)

The common estuarine fish species Fundulus heteroclitus or Mummichog has long been used in ecotoxicological studies; however, their periodic spawning pattern is perceived to limit their use in reproductive bioassays and the availability of sensitive life stages. This study evaluated the lunar periodicity of spawning, egg production, and changes in gonadosomatic index (IG) in the laboratory using wild and F1-generation Mummichogs that originated from three different geographic areas: the northern extreme part of their geographic range (New Brunswick, Canada; 45°N), the middle of the northern subspecies range (Massachusetts, USA; 41°N), and within the southern subspecies range (Virginia, USA; 37°N). Unlike some previous studies of wild and laboratory-held fish, Mummichogs from all locations were continuous spawners over a prolonged period of time (8+ weeks) under laboratory conditions. However, there was greater variance in egg production in smaller fish (≤70 mm total length) compared to larger fish. Our re...

Seasonal patterns of gonad size, liver size, and in vitro gonadal steroidogenic capacity in slimy sculpin (Cottus cognatus)

The objective of this study was to characterize the reproductive seasonality of slimy sculpin (Cottus cognatus), a small-bodied, benthic spring spawning species. Sculpin are unique compared with other temperate fish species because they have a reproductive pattern where gonadal maturation occurs over winter in northern areas of its distribution. Previous studies have involved pre-spawning sampling (early spring in North America) and post-spawning sampling (early fall in North America). However, seasonal changes in gonadosomatic index, hepatosomatic index, condition factor, and in vitro gonadal production of estradiol (E2) and testosterone (T) in females and T and 11-ketotestosterone (11-KT) in males have not been characterized. Following a summer quiescent period, female sculpin showed an increase in gonadal hormone production during the fall, which was associated with increases in gonad and liver sizes, however males experienced a much shorter resting phase following spawning in May. Elevated production of both T and 11-KT appears to both signal the initiation of gonadal growth in September and contribute to gonadal maturation over the winter. This study is important because it is the first characterization of the seasonal reproductive pattern in sculpin and it describes the patterns of gonad development and seasonal changes in condition and liver size in this species as it prepares for spawning.

Changes of gonadosomatic index and plasma levels of cortisol in the male and female captive Caspian brown trout, Salmo Trutta Caspius (Kessler, 1877) during the reproductive cycle

The changes of cortisol and gonadosomatic index (GSI) in male and female Caspian brown trout reared under confinement in the hatchery were determined by radioimmunoassay. When the GSI reached to its maxima (for males: 17.2±1.9 ng/mL; for females: 15.6±4.7 ng/mL), the concentration of cortisol showed a clear peak both in males (10.6±0.8%) and females (10.1±0.9%). This result suggests that the elevated plasma levels of cortisol may not just be due to stresses during the breeding season but also due to its physiological functions in the reproduction of Caspian brown trout.

The effects of 17-α-ethinylestradiol (EE2) on molecular signaling cascades in mummichog (Fundulus heteroclitus)

Exposures to ≤10ng/L of 17-α-ethinylestradiol (EE2) will reduce or shut down egg production in freshwater fish models, while mummichog (Fundulus heteroclitus), an estuarine species, are able to produce eggs at EE2 concentrations >3000ng/L. The objective of this study was to gain mechanistic insight into how mummichog are able to produce eggs during exposures to high EE2. Mummichog were exposed to 0, 50 or 250ng/L of EE2 for 14d. There were no changes in gonadosomatic index, liversomatic index, gonad development, or plasma estradiol levels after exposure to EE2. However, testosterone significantly decreased with EE2 exposures (50, 250ng/L). Microarray analysis in the liver revealed that cell processes associated with lipids were affected by EE2 at the transcriptome level. Based on the transcriptomics data, we hypothesize that mummichog are able to maintain lipid transport and uptake into the ovary and this may be associated with apolipoproteins, facilitating normal oocyte development. Novel gene regulatory networks for protein modification targets were also constructed to learn more about the potential roles of estrogens in the teleost liver. Although post-translational modifications (PTMs) are important regulatory mechanisms, the roles of PTMs in protein regulation in fish and the susceptibility of PTMs to aquatic pollutants are largely unexplored and may offer novel insight into mechanisms of endocrine disruption.

The reproductive cycle of a deep-sea eel, Nettastoma melanurum (Nettastomatidae: Anguilliformes) from the south-eastern Sardinian Sea (central-western Mediterranean)

The reproductive cycle of the deep-sea eel Nettastoma melanurum was described based on 397 specimens (171 males and 226 females). Experimental trawl surveys between depths of 772 and 1598 m and commercial hauls (580–600 m) on compact mud bottoms off the south-eastern Sardinian waters (central-western Mediterranean) were carried out. The Sardinian catches did not indicate any particular trend of size-range in relation to depth in both sexes and seem to be sexually dimorphic with females growing almost 9 cm longer than males at maximum lengths. It was a dioeceous and an oviparous deep-sea species. For females and males, six stages of oocyte development, characterizing the different stages of maturity, were identified. Histological examination demonstrated that ovaries of N. melanurum showed a ‘group-synchronous’ pattern, highlighting a type of monocyclic ovary. The species showed a size at first maturity of 53.5 cm and 50.5 cm total length in females and males respectively. The reproductive period appeared to be unique and well defined in both sexes. Their monthly changes of gonadosomatic index and maturation phases of ovaries and testis showed that the species was in a resting period from March to July. Vitellogenesis and spawning began in September and ended in January. Nettastoma melanurum seemed to be a fecund species (8132–18755 eggs).

In vivo response of melatonin, gonadal activity and biochemical changes during CYP19 inhibited sex reversal in common carp Cyprinus carpio (L)

CYP19 aromatase is the key enzyme in vertebrate steroidogenesis, catalyzing the conversion of C19 androgens to 17β-estradiol (E2). The objective of the present study was to assess the effect of the CYP19 inhibitors (AIs) fadrozole and anastrozole on gonadal development and sex differentiation in Cyprinus carpio and investigate the possible involvement of in vivo melatonin (MLT) production during sex differentiation. The CYP19 activity in 30 day-post fertilized (30 dpf) fingerlings was inhibited by treating with fadrozole and anastrozole in doses of 100mg/kg and 200mg/kg of feed. Gonado-somatic-index (GSI) of fish decreased (P<0.005) and the changes in GSI was dose dependent. Serum testosterone (T) concentration increased (P<0.001) after AI treatments and was negatively correlated with serum E2 concentration which decreased (P<0.005). Morning serum MLT concentration decreased during the period of inhibited CYP19 activity with a positive correlation with E2 concentration. Sex-ratio in anastrazole (200mg/kg) treated fish were 98.1% males while with fadrozole treatment at the same dose resulted in a 97.1% masculinization. Histological examination of fadrozole-treated fish gonads resulted in detection of atretic follicles and intensified spermiation. The protein and lipid production was depressed in AIs-treated fish. The results suggested that fadrozole and anastrozole both effectively inhibited oogenesis and ovarian development in C. carpio accelerating testicular formation. There was a physiological correlation between CYP19 activity, E2 and MLT synthesis during gonadal development and sex differentiation.

Effect of dietary protein and lipid levels on gonadal development of female redclaw crayfishCherax quadricarinatus

The effect of two crude dietary protein (26% and 32% P) and two lipid levels (4.7% and 12% L) on gonadal development of female redclaw crayfish Cherax quadricarinatus was determined. The gonadosomatic index (GSI), hepatosomatic index (HSI), biochemical composition of gonad and hepatopancreas, oocyte diameter and frequency of the developmental stage of oocytes were analysed. The GSI was significantly less using 26% P to 4.7% L. A significant interaction between P and L content was found for GSI. A significantly higher HSI value was obtained when L was 12%. P content in the hepatopancreas was significantly higher using 32% P and 4.7% L. The maximum L content in the hepatopancreas was obtained from the 32% P and 12% L diet. A significant interaction between P and L content was found for L content in the hepatopancreas. A higher frequency of post-vitellogenic oocytes was obtained with diets containing 32% P. There was an interaction between dietary P and L level causing lipid accumulation in the hepatopancreas and changes in GSI. For an optimum 32% P, excess dietary lipid is bioaccumulated in the hepatopancreas, indicating that there is excess available energy. When the P and L levels are restricted, there is a limited gonad development, thus affecting overall reproduction in female C. quadricarinatus.

Gonadal development and associated changes in gonadosomatic index and sex steroids during the reproductive cycle of cultured male and female Caspian brown trout, Salmo trutta caspius (Kessler, 1877)

Reproductive cycle in female and male Caspian brown trout (Salmo trutta caspius) was investigated by sampling blood plasma and gonadal tissue from 4-year-old fish. The reproductive cycles of both female and male Caspian brown trout are characterised by distinct variations in gonadal size and developmental stage and these are associated with changes in sex steroids. In females, ovarian development progressed merely until vitellogenesis stage while male fish completed testicular development and produced milt at January. Milt had good quality in terms of percentage and duration of motility, milt volume and sperm density. In females, the average diameter of the largest follicles increased steadily throughout the course of experiment and was coincident with changes in the concentration of sex steroids. Beginning in September, plasma testosterone (T) elevated from October to November and then remained unchanged until the end of the experiment. With a one month lag than T, the increasing trend of plasma estradiol (E2) was observed in September to October and then E2 levels decreased steadily for the rest of the experimental period. Plasma progesterone (P) levels were low throughout August to November, but sudden increases were observed during December and January. The concentrations of plasma calcium (Ca) increased significantly during October and November but then declined steadily until the end of experiment. In males, Plasma T increased rapidly, culminating in a transient peak in December. This peak was followed by a steady decline afterwards. Such increasing pattern was observed after October for P. Although E2 concentrations were low throughout the experiment, a weak peak was observed in October. The gonadosomatic index increased continuously for both female and male Caspian brown trout during gonadal development. In conclusion, our results showed that unlike 4-year-old female Caspian brown trout, the male fish can complete final maturation under cultural conditions in the hatchery. Probably, female fish would acquire this ability in ages more than 4 years.

Changes in hormonal profile, gonads and sperm quality of Argyrosomus regius (Pisces, Scianidae) during the first sexual differentiation and maturation

In the present study, sexual gonadal differentiation and first sexual maturation of Meagre (Argyrosomus regius) was studied, based upon the annual changes in gonadosomatic index (GSI), gonadal histology, and the plasma steroid hormones, testosterone (T), 11-ketotestosterone (11-KT), and estradiol (E2). In addition, spermatozoa characteristics were evaluated by measuring sperm motility and morphology. Results demonstrated that Meagre completes sex differentiation at 10 to 12 mo of age, and are group-synchronous spawners, which reach puberty at 2 (mean length 26.8 ± 0.7 cm, mean weight 920 ± 75 g; N = 10) and 3 (mean length 35.8 ± 0.8 cm, mean weight 1610 ± 89 g; N = 10) years of age for males and females, respectively. In males, during the sex differentiation period, T levels were significantly higher with respect to those of 11-KT; this suggests that T has a key role in the early phases of the sex differentiation. During the spawning season an increase in plasma concentrations of all hormones was observed with 11-KT levels being significantly higher that those of T. In females, during the sex differentiation period, there was an increase in E2 plasma levels, while during the first spawning season, a significant increase of T and E2 levels were measured. Regarding sperm characteristics, the measured curvilinear velocity (VCL) and straight-linear velocity (VSL), resulted in the same order of magnitude with respect to those measured in other marine fish, while the average path velocity (VAP) was similar to that measured in the European Eel. The head of Meagre spermatozoa presents as oval shaped with a surface area of approximately 3.66 μm2 and a perimeter of approximately 6.65 μm. All these findings represent an important basis for further investigation on the reproductive biology of this specie and may assist the farmers to improve seed production in aquaculture.

Effects of hydrostatic pressure on monoaminergic activity in the brain of a tropical wrasse, Halicoeres trimaculatus: Possible implication for controlling tidal-related reproductive activity

Most wrasse species in tropical waters exhibit daily spawning synchrony with a preference for high tide. Fish perceive tidal rhythm cues through sensory organs and activate the brain–pituitary–gonadal endocrine axis for synchronous gonadal maturation, although how the tidal-related spawning cycle is controlled endogenously is not known. The purpose of this study was to examine whether hydrostatic pressure has an impact on brain monoamine levels and reproductive activities in the threespot wrasse Halichoeres trimaculatus. The contents of dopamine (DA), 3,4-dihydroxyphenylacetic acid (DOPAC), serotonin (5-HT), and 5-hydroxyindoleacetic acid (5-HIAA) in the brain were measured using high-performance liquid chromatography and an electrochemical detection system. Exposing the fish to hydrostatic pressure occurring at a 3-m depth (∼30 kPa) resulted in an increase in 5-HIAA/5-HT over 3 h and a decrease in DOPAC/DA over 6 h. No changes in gonadosomatic index or oocyte diameter were observed between the groups when female fish were reared at 0-m and 3-m depth for 3 h. Hydrostatic pressure did not alter pituitary mRNA abundance of follicle stimulating hormone-β or luteinizing hormone-β. However, in vitro culture of ovaries from pressurized fish in the presence of human chorionic gonadotropin resulted in an increase in 17α,20β-dihydroxy-4-pregnen-3-one in the medium. These results suggest that hydrostatic pressure activates oocyte maturation through brain monoaminergic activity in this tropical wrasse species.

Aspects of the reproductive biology of two archer fishes Toxotes chatareus, (Hamilton 1822) and Toxotes jaculatrix (Pallas 1767)

Various aspects of the reproductive biology of two archer fishes Toxotes chatareus and Toxotes jaculatrix were studied to describe gonad development, spawning season, sex ratio, and fecundity. Spawning season was assessed using monthly changes in gonadosomatic index (GSI) and histological inspection of the gonads. Both species exhibit two modes of oocytes; a mode of small primary growth oocytes and a single mode that increases with size as oocytes sequester vitellogenin and undergo maturation, showing the synchronous oocyte development typical of total spawners. Based on GSI values and advanced stages of oocyte maturity, T. chatareus and T. jaculatrix, females appear to spawn from November to December. The average fecundity of female T. chatareus was 55 000 ± 5538 eggs, and T. jaculatrix was 50 000 ± 3440 eggs; fecundity ranged from 20 000 to 150 000 eggs for both species, with relative fecundities of 600 to 1100 eggs/g body weight, and a mean value of 800 ± 32 for T. chatareus; relative fecundity ranged from 500 to 1100 with a mean value of 700 ± 23 for T. jaculatrix. Sex ratio, defined as the proportion of males to females, was 2.2 and 2.5 in T. chatareus and T. jaculatrix, respectively. The apparent abundance of males in samples could be due to females being positioned lower in the water column and therefore being sampled less frequently. Our results indicate that in both species, spawning occurs between the months of November and December during the monsoon season, which provides the mangrove coastal waters inhabited by these species with an abundance of food resources and additional floodplain nursery habitat for larvae and juveniles.

The Reproductive Biology of Siscowet and Lean Lake Trout in Southern Lake Superior

AbstractLean and siscowet morphotypes of lake trout Salvelinus namaycush in Lake Superior are thought to be genetically separate, but the reproductive isolating mechanism is unknown. The testicular and ovarian cycles and reproductive hormone levels of these morphotypes were determined from May to October in populations east and west of the Keweenaw Peninsula in southern Lake Superior. The gonadosomatic index (GSI) increased from August to October for lean and siscowet males and females east of the Keweenaw Peninsula and for siscowets west of the Keweenaw Peninsula. Circulating estradiol‐17β (E2) levels and ovarian GSIs increased simultaneously in females of both morphotypes. However, circulating 11‐ketotestosterone (11‐KT) levels in lean and siscowet males were not significantly elevated until October even though testicular GSIs increased by August. Transcripts of the follicle stimulating hormone (FSH) beta subunit (an indirect measure of FSH activity) increased in lean and siscowet males and females during August and September, when GSIs were increasing for both morphotypes. The seasonal changes in GSIs and hormone levels indicate that both lean and siscowet individuals in southern Lake Superior populations undergo reproductive maturation at the same time in the fall; therefore, reproductive timing does not appear to genetically isolate the morphotypes in these populations. A proportion of the sampled females (lean lake trout: 54%; siscowets: 42%) exhibited no increase in GSI from August to October, strongly suggesting that in any given year some proportion of the population does not reproduce. This was also observed in males but at a lower percentage (19–20%). Fish that did not have maturing gonads from August to October also had lower E2 and 11‐KT levels than maturing fish. Fecundity measured for lean and siscowet lake trout was not statistically different and was similar to historical values.

Studies on reproduction of the mullet Mugil platanus Günther, 1880 (Actinopterygii, Mugilidae) from the Mar Chiquita coastal lagoon, Argentina: Similarities and differences with related species

The aim of the present study is to provide the first results on the reproductive biology of Mugil platanus, from the Mar Chiquita coastal lagoon (Argentina). To address this topic, we employed mainly female gonads, at both microscopic and macroscopic levels. The following stages of oocyte development were observed: (A) oogonias, (B) primary growth oocyte, (C) cortical alveolus stage, (D) yolked oocytes, and (E) atretic follicle. Also five of the seven stages of gonad maturity were macro and microscopically stated. The potential fecundity ranged between 1,002,026 and 2,548,769 yolked oocytes, with a mean of around 1,800,000 oocytes. The length at first maturity (L50) was 450.6 total length (TL) and 367.7 standard length (SL) for females, 436.3 TL and 354.9 SL for males, showing a late sexual maturity for both sexes. Seasonal changes in gonadosomatic index (GSI) of females were observed. The mean GSI was ≤1 during six months of the year (January, June–October). Two modes in the ovarian maturation were observed, the most important in April–May and a secondary one in November–December. Both modes, correlated with the CPUE values, are indicative of the mullet migration from the coastal lagoon towards the sea for spawning. Differences and similarities have been found between Mugil platanus and other mugilid species (Mugil cephalus, Mugil curema, Liza aurata, Liza abu, Liza argentea, Myxus elongatus, and Valamugil cunnesius), from the reproductive point of view. The length at first maturity obtained for M. platanus is higher than in other mugilid species and when a relationship between maximum length and L50 is established the percentage corresponding to Mugil platanus is 75%, while the others range between 50 and 61%.

Influence of dietary carbohydrate level on endocrine status and hepatic carbohydrate metabolism in the marine fish Sparus sarba

Silver sea bream, Sparus sarba, were fed two diets of different carbohydrate levels (2 and 20% dextrin) for 4 weeks, and the effects on organ indices, liver composition, serum metabolite and hormone levels and gene expression profile of key enzymes of carbohydrate metabolism in the liver were investigated. By using real-time PCR, mRNA expression levels of carbohydrate metabolic enzymes including glucokinase (GK, glycolysis), glucose-6-phosphatase (G6Pase, gluconeogenesis), glycogen synthase (GS, glycogenesis), glycogen phosphorylase (GP, glycogenolysis) and glucose-6-phosphate dehydrogenase (G6PDH, pentose phosphate pathway) in liver of sea bream have been examined, and it was found that high dietary carbohydrate level increased mRNA level of GK but decreased mRNA levels of G6Pase and GP. However, mRNA levels of GS and G6PDH were not significantly influenced by dietary carbohydrate. Silver sea bream fed high dietary carbohydrate had higher hepatosomatic index (HSI), liver glycogen and protein, but there were no significant changes in gonadosomatic index (GSI), serum glucose and protein level, as well as liver lipid and moisture level. Pituitary growth hormone (GH) and hepatic insulin-like growth factor I (IGF-I) transcript abundance were assayed by real-time PCR, and it was found that both parameters remained unchanged in fish fed different dietary carbohydrate levels. Serum triiodothyronine (T(3)) and thyroxine (T(4)) were not significantly affected by dietary carbohydrate levels, but lower serum cortisol level was found in fish fed high dietary carbohydrate level. These results suggest that silver sea bream is able to adapt to a diet with high carbohydrate content (up to 20% dextrin), the consumption of which would lead to fundamental re-organization of carbohydrate metabolism resulting in hepatic glycogen deposition.

Use of portable ultrasonography to determine ovary size and fecundity non-lethally in northern pike (Esox lucius) and white sucker (Catostomus commersoni)

The objective of this study was to investigate the feasibility of using field-based portable ultrasonography to accurately estimate ovary weight, gonadosomatic index (GSI) and fecundity in large-bodied fish species. These reproductive endpoints were estimated using ultrasound on prespawning female northern pike (Esox lucius) and white sucker (Catostomus commersoni) and compared with actual measured values determined post mortem. Using five cross-sectional ultrasound images in pike, estimated ovary weight and fecundity, but not GSI, were significantly correlated with measured values. All endpoints were overestimated by 21 to 23% using ultrasound in pike. In a subsequent experiment using 20 cross-sectional ovary images, estimated ovary weight, GSI and fecundity were significantly correlated with measured values in white sucker. Although underestimated by 5 to 12% using 20 cross-sectional images, there were no statistical differences among estimated and measured mean ovary weight, GSI and fecundity in white sucker using this approach. Based on the variances for GSI estimations in both species, power analysis indicated that the ultrasound technique could detect a 25% change in GSI using sample sizes of &amp;lt;20 fish. This study illustrates the utility of portable ultrasonography as a promising non-lethal technique for assessing reproductive endpoints in the field.

Tödürge gölü’ndeki (Sivas) cyprinid hibritlerinin [S. cephalus (l.) x A. chalcoides (g.)] üreme biyolojisi

In present study, the different reproductive properties of hybrids of Squalius cephalus x Albur-nus chalcoides which occured under natural conditions, were determined. Firstly, the sexual maturity ages for males and females were indicated. The reproductive period was defined ac-cording to the monthly changes of gonadosomatic index, gonad weight, egg diameter and egg number in per gram of ovarium. Mean fecundity was determined for each age group. Both fe-males and males were attained sexual maturity at II age. The values of fork length for the smallest female and male with mature gonads were measured as 123 mm and 127 mm, respec-tively. The maximum value of mean gonadosomatic index for females was determined in May (9.48). However, in July the index revealed minimum values (0.92). The minimum and maxi-mum egg diameters were measured as 0.23 mm and 1.72 mm, respectively. Egg number in per gram of ovarium was changed between 516 and 2665. According to the monthly changes in the gonadosomatic index, gonad weight, egg diameter, and egg number in per gram of ovarium, it was determined that the spawning in hybrids of S. cephalus x A. chalcoides in Todurge Lake began in May and continued until end of July. Mean fecundity was determined as 2238 for II age group, and as 4250 for III age group. The values of fecundity of the hybrids were quite lower than the values of S. cephalus and A. chalcoides in the same age group.

Estrogenic effects of octylphenol on carp (&lt;I&gt;Cyprinus carpio&lt;/I&gt;)

The aim of the study was to investigate the estrogenic effects of octylphenol (OP) on carp (Cyprinus carpio). Vitellogenin (Vtg) and the parameters of growth and development were determined as biomarkers. The one-year-old carp from a large reservoir were kept in the laboratory for 7 days. Then they were exposed to OP under semi-static conditions for 32 days. They were fed once a day. The water temperature was (18±1) ℃ during the experiment. Five concentrations of OP at 10,50,100,300 and 500 μg/L were selected for this study. The mortality,abnormal behavior and appearance of the carp were recorded during the exposure. At the end of the exposure,fish were sampled to measure body weight,body length and gonadal weight,then plasma and liver homogenates were prepared for the determination of Vtg concentration by ELISA. The data were analysed with SPSS 11.5. At the end of exposure,it was found that there was no significant difference in the survival and growth of the fish. The exposure to OP caused obvious changes in gonadosomatic index (GSI). In accordance with the increase of the OP concentration,the GSIs of female carp increased,while that of male carp decreased. OP at 10 μg/L caused the GSIs of male carp decreased significantly (P0.05). The GSIs of female carp increased significantly when the OP concentration reached 50 μg/L (P0.05). OP induced the synthesis of Vtg in male carp. Vtg was not detected in plasma or liver homogenates in control groups,and it was detected in some of the samples in 10 μg/L group. The Vtg levels increased greatly when the OP concentration reached 50 μg/L (P0.05). The Vtg levels in 500 μg/L group were significantly lower than those in 300 μg/L (P0.01),but significantly higher than those in 100 μg/L group (P0.01). The results indicated that octylphenol (OP) has obvious impact on the gonadal development of carps. It can induce Vtg synthesis in male carps. OP has visible estrogenic effects on carp (Cyprinus carpio) although it did not affect the growth of the fish at low exposure concentrations.

Annual Life Cycle of Adult Marbled Sole Pleuronectes yokohamae in the Coastal Waters around Kikonai Bay, Hokkaido, Japan

To clarify the annual life cycle of adult marbled sole Pleuronectes yokohamae in the coastal waters around Kikonai Bay, the seasonal changes in gonadosomatic index, hepatosomatic index, and condition factor of samples obtained with commercial set nets and research bottom trawl nets during May 1994 through October 1996 were examined. In addition, feeding intensity was investigated using a stomach contents index and noting the percentage of empty stomach. The annual life cycle of adult P. yokohamae was divided into the.following three periods: spawning (February - April), active feeding and recovering (May - July), and inactive feeding (August­ January). The inactive feeding period was further divided into two sub-periods: immature (August - October) and mature (November - January). It seems likely that P. yokohamae in this study area feeds intensively after spawning and matures under these high levels of nutrition.

Breeding strategy of Acrossocheilus fasciatus in the Puxi Stream of the Huangshan Mountain

Abstract Breeding strategies of Acrossocheilus fasciatus were studied from 592 specimens collected monthly during May 2007 and April 2008 in the Puxi Stream of the Huangshan Mountain. Sex ratio of the studied population was 0.90 : 1 (♀ : ♂), not significantly different from 1:1. Both sexes reached their first sexual maturity at age 2 (the second calendar year of their birth). Fifty percent of females and males reached maturity at a total length of 69.75 mm and 69.36 mm respectively, and the minimum total length was 61.54 mm and 58.96 mm, respectively. Based on the monthly changes in gonado-somatic index and egg-development process, the breeding season of the population was from May to August, with one obvious interval (in June) occurring in the breeding activity for the females. The nonsynchronous development of oocytes observed in mature ovaries indicated that A. fasciatus is a batch spawner. Absolute fecundity of A. fasciatus ranged from 308 to 2002 eggs with a mean of 857 eggs, increased significantly with total length, and was significantly different among three age groups. Relative fecundity ranged from 38.63 to 71.70 egg/g with a mean of 53.29 egg/ g, and was not significantly different among the three age groups. It was suggested that these reproductive characteristics were adaptive strategies for A. fasciatus to acclimatize to lotic water where environmental factors were unstable but predictable.

Age and Growth of the Elongate Ilisha Ilisha elongata

We present age and growth data for Ilisha elongata, based on 363 specimens caught in 1999 and 2000 around Jeju Island and the southwest coast of Korea. Scale and ring radii of each ring group showed a direct one-to-one relationship, with ring radius increasing as scale radius increased. The relationship between fork length and scale radius was FL=39.553SR+60.935 for females, FL=39.474SR+54.026 for males, and FL=39.608SR+57.547 for both sexes. Monthly changes in the marginal index indicated that a new ring appears once each year (in July). Maximum age, mean age and mean fork length of fish were 10 years, 5.0 years, and 349mm, respectively. Von Bertalanffy's growth equations were <TEX>$FL_t=495.4{\times}[1-\exp(-0.2586(t+0.6487))]$</TEX> for fork length (mm) and <TEX>$W_t=1,112.5{\times}[1-\exp(-0.2586(t+0.6487))]^{2.874}$</TEX> for body weight (g) for both sexes. Monthly changes in the gonadosomatic index (GSI) indicated that the spawning period was in June and July, which corresponded closely with ring formation time. Differences in monthly GSI changes in 1999 and 2000 may be related to water temperature variation. Fecundity ranged from 5,664 to 176,290 eggs per individual (n=43, fork length 264-470mm). The relationship between fecundity(F) and fork length was <TEX>$F=7.7{\times}10^{-7}{\times}FL^{4.9269}$</TEX>.