Male Gonadosomatic Index Research Articles

Reproductive Mode of Fejervarya limnocharis (Anura: Ranidae) Caught from Mae Sot, Thailand Based on Its Gonadosomatic Indices.

Amphibians show a variety of reproductive modes and strategies. The cyclicity and continuity of reproduction can often be predicted from the annual gonadosomatic index trends in a species specific manner. This research aims to document the female and male gonadosomatic index profiles and to ascertain the reproductive cyclicity or continuity of Fejervarya limnocharis (Anura: Ranidae) caught in Mae Sot, Tak Province, Thailand. Frogs were collected monthly between November 2007 and October 2009 in rice fields and their surrounding areas in the study site. For each frog, total weight and ovarian/testicular weight were measured to obtain the female and male gonadosomatic index. The number of female individuals with mature eggs (postvitellogenic eggs) was also counted. The results showed that female frogs had two main surges of increased GSI in March and September of 2008. Alternatively, male frogs showed a more gradual increase and decrease in gonadosomatic index, thus the index remaining high throughout the year. This study concluded that while F. limnocharis in this area is essentially a continuous breeder, it is more optimized for a cyclic reproduction mode with two breeding cycles during the rainy season.

Annual Reproductive Cycle and Spawning Behavior of Chameleon Goby, Tridentiger Trigonocephalus in Korea

Introduction: Gobiid fish are appropriate species for investigating the effects of endocrine disrupting chemicals with their small size, easy to handle, and strong tolerance [1]. Chameleon goby, Tridentiger trigonocephalus is distributed in mud flat, brackish waters of western and southern Korea, China and Japan [2]. At present, there is very little knowledge about its reproductive characteristics. In this study, we investigated the annual reproductive cycle and spawning behavior of chameleon goby. Methods: In the field investigation, fishes were sampled monthly from the seagrass bed of Dongdae Bay (southern coastal waters of Korea) between April 2009 and March 2010. Gonadosomatic index (GSI) was recorded and gonads were removed and fixed in Bouin’s solution and processed for light microscopy. For observation of spawning process from indoor tank, sexually mature fish were held under an artificial light and temperature regime. Fertilized eggs and guarding male were transferred to incubation tanks until hatching. Results: GSI of females increased from April and peaked in May (16.31±2.16), then decreased from June and were the lowest value in August (0.34±0.0). GSI of males increased from April and peaked in July (1.17±0.35), then decreased dramatically in August (Fig. 1). In histological observation, the annual reproductive cycle can be divided into four successive stages in females: the growing (November-March), maturing (April-May), ripe and spawning (June-July), and recovery (AugustOctober) stages. Males passed through growing (November-March), maturing (April-June), ripe and

Reproducción y dinámica poblacional de Cheirodon interruptus (Ostariophysi: Characidae) en el arroyo El Portugués, alta cuenca del río Samborombón, Argentina

The reproductive period of Cheirodon interruptus was determined by analyzing 1658 individuals collected monthly in the stream El Portugues, Argentina, from May 2004 to April 2005. Two prolonged spawning seasons, one in spring and another in autumn, were observed based on the maturity stages and gonadosomatic index (GSI) of female specimens. The mean monthly GSI of males was significantly correlated with depth. In females, the GSI exhibited a significant correlation with photoperiod and depth. The remaining environmental variables, including temperature, pH, conductivity, and monthly rainfall, did not show a correlation with the mean monthly GSI. The first sexual maturity in females and males was reached within the 24-26 mm standard length class. The mean absolute fecundity was 448 oocytes (SD = 217.8), and the mean relative fecundity was 0.33 (SD = 0.097) oocytes per milligram of body weight; this species is a multiple spawner. The oocyte diameter ranged from 0.05 to 0.70 mm, with a mean of 0.48 mm (SD = 0.16).

Size matters: importance of penis length variation on reproduction studies and imposex monitoring in Bolinus brandaris (Gastropoda: Muricidae)

The present study aimed at analysing the monthly variation in penis length (PL) during the reproductive cycle of the purple dye murex (Bolinus brandaris). Two hypotheses were tested: PL variation reflects male maturation and reproductive activity; PL variation bias the calculation of imposex indices based on penis measurement (RPLI and RPSI). Sampling was performed during 1 year in a population from Ria Formosa lagoon (Algarve coast, southern Portugal) with high incidence of imposex. Penis-bearing individuals were measured for shell length (SL) and PL, and two bio-physiological indices were calculated for both sexes, the general condition index (K) and the gonadosomatic index (GSI). PL presented monthly variation in both sexes, but while female PL showed small and random oscillation, male PL exhibited significant variation throughout the reproductive cycle (as evidenced by the similar and synchronous trends between male PL and GSI). These findings have implications both for reproduction studies and imposex monitoring: calculation of standardised PL (PL/SL) allows for gender identification without killing the organism and constitutes a useful penial index for assessing male maturation and reproductive activity; RPLI and RPSI should be applied cautiously in spatial and temporal comparisons of imposex severity in B. brandaris.

New biological data on the brown ray, Raja miraletus (Chondrichthyes: Rajidae), off the coast of Senegal (eastern tropical Atlantic)

A total of 483 specimens (236 males and 247 females) of the brown ray Raja miraletus were collected off the coast of Senegal (eastern tropical Atlantic). The hepatosomatic index (HSI) and gonadosomatic index (GSI) were calculated in both males and females, and the oviducosomatic index (OSI) in females. Both HSI and GSI increased significantly with specimen size and the three maturity stages considered (juveniles, subadults, and adults). The monthly HSI of adult males did not show significant variations throughout the year. In contrast, the HSI of adult females, GSI of both adult males and females, and OSI of females showed significant variations throughout year. This suggests that monthly variations occurred in the production of gonadal products even though vitellogenetic activity was observed throughout the year.

EFFECT OF SOURCE AND LEVEL OF DIETARY WATER HYACINTH ON NILE TILAPIA, Oreochromis niloticus, PERFORMANCE

A feeding laboratorial trial in glass aquaria for 12 weeks, to replace graded levels of water hyacinth (WH) meal protein from two (polluted and not polluted) water sources instead of 0, 10, 20, 30 and 40% of soybean meal protein in Nile tilapia diets. Ten experimental diets were formulated to be isocaloric and isonitrogenous (26% crude protein) and offered daily at 2 meals, 6 days a week at 3% of fish biomass daily. Results indicated that rearing water did not influence fish by the tested treatments. Most tested heavy metals had higher levels in WH and diets especially those of polluted source. Iron levels of the WH and experimental diets were > those of Mn > Zn > Cu > Pb > Cd. The highest ether extract (EE) and nitrogen free extract (NFE) and the lowest ash contents were realized in diet contained 30% replacement with WH leaves protein from non-polluted source. Growth performance parameters differed significantly as affected by WH source and level, so the final body weights (FBW) in treatments contained 10, 20 and 30% replacement with WH levels meal protein from the polluted source were significantly lower than those of WH from the non-polluted source. Also, the pollution source for WH led to significantly lower other growth performance parameters than those of the unpolluted source for WH, whether for the bodyweight gain (BWG), survival rate (SR), or specific growth rate (SGR). Increasing level of WH leaves meal protein in the experimental diets led to significantly lower FBW, BWG, SR, SGR and condition factor. The pollution source of WH led to increases in the undeniable parts from the experimental fish (tissues' indices, hepato-somatic and female and male gonado-somatic indices), also more than 30% replacement negatively affected these indices. Contaminated source of WH decreased the feed conversion ratio (FCR) for the very low feed intake as well as for the low fish growth which led to apparent improvements in FCR, protein efficiency ratio (PER) and protein productive value (PPV). Increasing the substitution levels led to increased FCR and PPV but led to lower PER. All blood hematological and biochemical parameters of the tested fish significantly and negative influenced by source and level of WH in the experimental diets, except hemoglobin and total proteins' concentrations. Increasing level of WH leaves meal protein lowered blood total proteins in the fish as a result of lower quality of protein in such diets containing WH. Source and level of WH in the experimental diets significantly affected the chemical analysis of the whole fish body including CP, EE and ash contents. The CP decreased and both of EE and ash were increased by elevating the substation level or for dietary contaminated WH increased by elevating the substation level or for dietary contaminated WH inclusion. The increase in WH level in fish diets reduced the feed intake sharply particularly from the diets contained WH from the polluted source comparing with those contained WH from its non-polluted source. Although the low price of WH – included diets, particularly by increasing dietary WH levels; yet, the return from fish weight gain decreased, especially when WH was coming from its polluted source, which starkly reduced feed intake.

The maturity and breeding season of the bellybarred pipefish, Hippichthys spicifer, in Okinawa-jima Island rivers

We investigated the breeding season and size at maturation and described the morphology of newly released Hippichthys spicifer larvae collected from the estuaries of four rivers on northern Okinawa-jima Island, southern Japan. The minimum size of brooding males was 108 mm standard length (SL). The smallest mature female, as estimated from gonadosomatic index (GSI) analysis and histological observations of gonads, was about 100 mm SL. Histological observations showed the gonad of H. spicifer to be a cylindrical tube with a sequential pattern of follicle development and a single germinal ridge. We surmised that the breeding season is year-round, as shown by monthly changes in female GSI, gonad histology, and monthly changes in the occurrence of brooding males. The monthly changes in female GSI and proportions of brooding males were small in winter. The number of eggs in the male brood pouch ranged from 114 to 1,764 (604.4 ± 322.8, mean ± standard deviation; n = 25). The SL of the released larvae was 9.9 mm. All fins except the pectoral fins were formed, the body was elongated, and the developmental stage was similar to that of other Urophori species. The smallest individual present in the mangrove areas of estuaries was 78.0 mm SL.

Seasonal relationship between gonadotropin, growth hormone, and estrogen receptor mRNA expression in the pituitary gland of largemouth bass

The objectives of this study were to investigate the seasonal changes in pituitary gonadotropins, growth hormone (GH), and estrogen receptor (ER) isoform mRNA in wild female and male largemouth bass (LMB) ( Micropterus salmoides) from an unpolluted habitat to better understand reproductive physiology in this ecologically important species. Female pituitary luteinizing hormone (LH) β subunit and follicle stimulating hormone (FSH) β subunit mRNA showed significant seasonal variation with levels peaking from January to April and were lowest from May to August. Male LMB showed more variation in gonadotropin subunit expression from month to month. Females had approximately 2–3 times higher gonadotropin mRNA levels in the pituitary when compared to males. All three gonadotropin mRNAs in females were positively correlated to gonadosomatic index (GSI), but only LHβ mRNA was correlated to GSI in males. Gonadotropin mRNA expression also increased with increasing oocyte and sperm maturation. Gonadotropin β subunit mRNA expression was positively correlated to GH mRNA in both sexes. The expression of all three ER isoforms was significantly correlated to each other in both sexes. The concurrent increase in all three ER mRNA isoforms with increasing gonadotropin mRNA in females and males suggests a prominent role for E2 feedback on pituitary gonadotropin synthesis in both sexes and that each of the three ER isoforms are likely to play a role in the pituitary during teleost reproduction.

Visual communication stimulates reproduction in Nile tilapia, Oreochromis niloticus (L.)

Reproductive fish behavior is affected by male-female interactions that stimulate physiological responses such as hormonal release and gonad development. During male-female interactions, visual and chemical communication can modulate fish reproduction. The aim of the present study was to test the effect of visual and chemical male-female interaction on the gonad development and reproductive behavior of the cichlid fish Nile tilapia, Oreochromis niloticus (L.). Fifty-six pairs were studied after being maintained for 5 days under one of the four conditions (N = 14 for each condition): 1) visual contact (V); 2) chemical contact (Ch); 3) chemical and visual contact (Ch+V); 4) no sensory contact (Iso) - males and females isolated. We compared the reproductive behavior (nesting, courtship and spawning) and gonadosomatic index (GSI) of pairs of fish under all four conditions. Visual communication enhanced the frequency of courtship in males (mean +/- SEM; V: 24.79 +/- 3.30, Ch+V: 20.74 +/- 3.09, Ch: 0.1 +/- 0.07, Iso: 4.68 +/- 1.26 events/30 min; P < 0.05, two-way ANOVA with LSD post hoc test), induced spawning in females (3 spawning in V and also 3 in Ch+V condition), and increased GSI in males (mean +/- SEM; V: 1.39 +/- 0.08, Ch+V: 1.21 +/- 0.08, Ch: 1.04 +/- 0.07, Iso: 0.82 +/- 0.07%; P < 0.05, two-way ANOVA with LSD post hoc test). Chemical communication did not affect the reproductive behavior of pairs nor did it enhance the effects of visual contact. Therefore, male-female visual communication is an effective cue, which stimulates reproduction among pairs of Nile tilapia.

Reproductive biology of the Neotropical electric fish Brachyhypopomus draco (Teleostei: Hypopomidae) from southern Brazil

The reproductive biology of a population of the weakly electric fish Brachyhypopomus draco from southern Brazil is described. Information is provided on the establishment of the reproductive period in this species and its relations with environmental and feeding factors, as well as on the absolute and relative fecundities, spawning type, sex ratio and sexual dimorphism. The species exhibits a relatively long reproductive period, a relative fecundity of 0.173 oocytes per mg of female total weight, and fractional spawning. The sex ratio did not differ from 1:1 during all sampled months. Sexual dimorphism related to hypertrophy of the male's distal portion of caudal filament was observed and males grew to greater lengths than females. Male gonadosomatic index (GSI) was significantly related to water depth, oxygen saturation and temperature. Female GSI was significantly related to water depth and hepatosomatic index.

Life History of Silver Perch Bairdiella chrysoura (Lacepède, 1803) in North-Central Gulf of Mexico Estuaries

Silver perch, Bairdiella chrysoura (Lacepède) [n = 485, 70.0–171.0 mm standard length (SL)] were collected from April 2002 through June 2003 in estuaries along the coast of Mississippi to quantify their life history. Ages estimated from sagittal otoliths ranged from 0 to 4 yr. Adult females were significantly longer and heavier than males at a given age. Silver perch became sexually mature at the end of their first year of life (0 yr), with 50% sexual maturity of the population occurring in the 91–95 mm SL size class. Gonadosomatic index (GSI) values for females began to increase in January and peaked in April (mean GSI = 11.99 ± 0.77), whereas mean male GSI values peaked in March at 1.70 (±0.11). Female silver perch were reproductively active for 6 mo, but peak spawning occurred from mid-March to June. Both oocyte maturation (OM) and postovulatory follicles (POF) were used to estimate spawning frequency. The OM method appeared to be the best estimate, paralleling most closely what was observed histologically, with spawning occurring every 1.25 d at the height of the season. Additionally, histological evidence suggested that 24% of the females sampled were capable of daily spawning. This life history information fills in data gaps to further the development of community-based models of estuarine systems, in turn facilitating best ecosystem management practices.

Reproduction of the lambariAstyanax scabripinnis(Jenyns, 1842) (Pisces: Characidae) in a small stream in Southeastern Brazil

Summary The reproduction of Astyanax scabripinnis captured bimonthly in the Cristais small stream (20 o 00¢03¢S and 43 o 56¢46¢W), in the Das Velhas River basin, was studied using gross anatomical and histological techniques. Standard length of females (56 ± 8 mm) was longer than males (49 ± 6 mm). The diameter of the nucleus of the primary spermatogonia was 7.5 ± 0.9 lm and of the spermatozoon head 1.8 ± 0.4 lm. For the females, the oogonia nuclei measured 10.2 ± 2.2 lm and the vitellogenic oocyte nuclei measured 675.0 ± 66.7 lm. The following stages of the reproductive cycle were established: developing, mature, partially spent ⁄ spawned and completely spent ⁄ spawned. Maximum number of males (61.3%) and females (58.2%) at the mature stage was observed during November ⁄ December. The gonadosomatic index of males and females was highest during the mature stage (2.4 ± 0.6; 7.5 ± 1.3, respectively) and decreased in subsequent stages. In females, the hepatosomatic index was highest during the developing stage (2.8 ± 0.3), and slightly decreased in the following stages. The highest stomach repletion index found for males was observed during the partially spent stage (2.0 ± 1.2), while for the females, this index varied discretely between the reproductive stages. The highest values of Fultons condition factor were registered during the mature stage in both sexes (2.9 ± 0.4 for males; 3.0 ± 0.3 for females). The continuous reproductive period and the presence of partially spawned females during the entire sampling period indicated that the species has fractional spawning.

Biological and fishery characteristics of rubberlip morwong Nemadactylus douglasii (Hector, 1875) in eastern Australia

Rubberlip morwong Nemadactylus douglasii are important members of temperate reef communities off south-eastern Australia where they are targeted by offshore commercial and recreational fisheries. Macroscopic gonad staging and gonadosomatic indices demonstrated that N. douglasii have a distinct autumn/winter spawning period. Males and females attained sexual maturity at approximately 24 cm fork length, corresponding to an age of approximately 3 years old. During the spawning period male gonadosomatic index values were of an order of magnitude smaller than those for females, suggesting that N. douglasii may belong to the group of cheilodactylids that are not group spawners. The method of counting opaque zones in sectioned otoliths to estimate age was validated using marginal increment analysis. The results showed that opaque zones in the otoliths of N. douglasii were similar to other cheilodactylids in this region and formed once each year during spring/early summer. Males grew at a similar rate to females until approximately 2 years of age, after which males grew faster and attained larger sizes. The longest and oldest fish observed during the study were 52.4 cm fork length and 22 years, respectively. N. douglasii were fully recruited to the commercial fishery by 4 years of age and the fishery was dominated (>93%) by fish between 3 and 15 years of age. The age composition in landings showed evidence of variable recruitment through time. The total instantaneous mortality rate was estimated using catch curve analysis and ranged between 0.27 and 0.37 yr −1. Natural mortality was estimated as 0.14 yr −1 based on the maximum observed age. Steady declines during the past three decades in the quantities and average sizes of N. douglasii in landings suggest that the stock has been substantially depleted.

Masculinization of the European sea bass ( Dicentrarchus labrax) by treatment with an androgen or aromatase inhibitor involves different gene expression and has distinct lasting effects on maturation

The objective of this study was to contribute to our understanding of the role of sex steroids in fish sex differentiation and male maturation. Sexually undifferentiated sea bass were administered 17α-methyldihydrotestosterone (MDHT), estradiol-17β (E 2), fadrozole (Fz), cyproterone acetate (CPA) or tamoxifen (Tx). MDHT produced 100% males whereas E 2 and Tx resulted in 100% females. Fz produced 95% males while CPA did not alter sex ratios. E 2 treatment did not affect gonadal aromatase ( cyp19a) expression levels, supporting the possibility that the feminizing effect of exogenous E 2 are not directly related to cyp19a regulation. Both MDHT and Fz decreased cyp19a expression. Moreover, androgen receptor ( ar) expression levels increased during development in all but the MDHT group, suggesting that early exposure to an androgen down-regulates subsequent ar expression in males and that Fz does not interact with the androgen receptor. Together, these observations indicate that although MDHT and Fz result in a similar phenotype, the molecular pathways involved are likely different, and show that Fz masculinization is the consequence of inhibited ovarian differentiation rather than of a direct androgenic effect. Further, since CPA did not alter sex ratios when administered during the period of highest androgen sensitivity, we suggest that androgens are not required for initial testicular differentiation in the sea bass. MDHT and Fz did not alter the number of precocious males but reduced and increased, respectively, their gonadosomatic index (GSI). In addition, Fz had lasting effects on the GSI of precocious and non-precocious males, probably due to alterations of estrogen function in the testis.

Comparison of Diploid and Triploid Largemouth Bass Growth and Maturation through Age 1 in Puerto Rico

AbstractTriploid largemouth bass Micropterus salmoides could be valuable both in sport fish management and in food fish production. This study compared the growth and reproductive development of diploid and triploid largemouth bass through age 1 in Lucchetti Reservoir, Puerto Rico. We produced and stocked 487 diploids and 477 triploids tagged with binary coded wire tags and recaptured these fish over 2 years. Growth rates, condition (relative weight (Wr)), and reproductive investment (gonadosomatic index (GSI)) were compared for diploid and triploid fish. Rates of mean daily growth did not differ between diploids (0.81 mm/d; SE = 0.07) and triploids (0.91 mm/d; SE = 0.09) as juveniles or overall through age 1. Diploid largemouth bass exhibited advanced reproductive development during age 1, while triploids did not. Mean GSI was higher for diploid females (mean = 1.98; SE = 0.81) than for triploid females (mean = 0.29; SE = 0.05), but male mean GSI did not significantly differ between the two groups. No difference in Wr was observed. Experimental fish in this study reached maturity in the middle of the spawning season at age 1 and therefore may not have reproduced. Additional research on triploid largemouth bass beyond age 1 is necessary to determine whether sterile triploids have growth advantages over reproductive adult diploids.

Length-Weight Relationships, Maturity, and Reproductive Season of the Fringelip Mullet Crenimugil crenilabis (Forsskål, 1775) from the Arabian Sea Coast of Oman

Fringelip mullet (Crenimugil crenilabis) caught at Al Duqum and Salalah in the Arabian Sea region of Omanwere sampled monthly between January 2001 and December 2002. The total length (TL) of mullet caught with gill- and seine nets ranged from 12 to 54.5 cm (32.4 cm mean ± SD; n = 2445) but &lt;2% of specimens had a TL&lt;24 cm, suggesting gear selectivity. Females dominated samples (1 : 0.36) and reached L at 32.8 cm TL (32.2 cm in males). Length weight relationships were non-linear and conversion factors between TL, fork length (FL) and standard length (SL) were calculated. Proportionately, most females had ripe gonads in September and October, and males in September to November. Both female and male gonadosomatic indices (GSI) peaked in September and October and were lowest between May and August. The peak in reproductive activity coincides with the fall intermonsoon, when the Arabian Sea upwellings caused by the onshore winds of the SW monsoon season (June to August/September) retreat. During this intermonsoon period the inshore water temperatures begin to rise after reaching a minimum in August/September. Some reproductive activity also occurs in other months, particularly February, when water temperatures are seasonally lower.

Quantitative Bioimaging Analysis of Gonads in olvas-GFP/ST-II YI Medaka (Transgenic Oryzias latipes) Exposed to Ethinylestradiol

This study investigates the adverse and persistent effects of ethinylestradiol (EE2) on mature gonads of transgenic olvas-GFPIST II-YI medaka (Oryzias latipes). The measurement of gonadal size calculating the GFP-fluorescent area was used as a technique that enabled monitoring gonads in living specimens by GFP fluorescence. First, mature medaka were exposed to EE2 (47.8-522 ng/L) for 4 weeks. The gonads showed a significant reduction of the GFP-fluorescent area and Gonadosomatic Index in males exposed to EE2 at >216 ng/L and females exposed at 522 ng/L. Histologically, males at all treatments exhibited testis-ova and additionally, high connective tissue prevalence at > or =216 ng/L. Next, mature male medaka were exposed to EE2 (43.7-473 ng/L) for 3 weeks and allowed to depurate for 6 weeks, to investigate persistent effects of EE2. Continuous gonad observation showed that GFP began to decline 3 weeks after initial exposure to > or =215 ng/L. After depuration, the gonad's fluorescent areas gradually recovered, with no statistical difference at the end of the depuration period; normal spermatogenesis was present in these individuals. Alterations in GFP fluorescence clearly indicate the condition of the gonad in transgenic medaka and this strain showed a facilitated screening fish model to detect the adverse effects on the gonad by estrogenic chemicals.

Reproductive strategy of Oreochromis niloticus (Pisces: Cichlidae) in Opa reservoir, Ile-Ife, Nigeria

The fish family Cichlidae has a large diversity and dominates African freshwater bodies, with over 200 species reported in inland waters. Sampling for the fish Oreochromis niloticus (Linnaeus) in Opa reservoir, Nigeria, started in October 1997 and extended until February 2000. The fishing methods employed for collecting the 1 430 specimens were cast netting and gillnetting. Egg diameter varied between 2.12 mm and 2.69 mm with a mean of 2.47+/-0.02. Female gonadosomatic index was 1.34+/-0.01 (0.12-4.06, n= 637). The male gonadosomatic index was 0.39+/-0.02 (0.03-1.67, n=789). In Opa reservoir, O. niloticus bred throughout the study period. The species was a maternal mouth brooder with the female fish carrying eggs and fry in the buccal cavities. The sex ratio of O. niloticus was approximately 1:1 in the reservoir. The fecundity of the species was between 73 eggs and 1 810 eggs per female with a mean fecundity of 815 eggs.

STUDIES OF ANNUAL GONADAL DEVELOPMENT AND GONADAL ULTRASTRUCTURE IN SPINY-CHEEK CRAYFISH (ORCONECTES LIMOSUS)

The aim of this study was to follow the gonadal development in freshwater crayfish Orconectes limosus (Rafinesque) by histological examination of ovaries and testes as well as monthly investigation of the gonadosomatic index over a period of one year. Male gonadosomatic index (IG) ranged between 0.11 to 0.79% with a minimum in July (0.11%) and maximum in September (0.79%) while in females it ranged between 0.25 to 6.15% with a minimum in July (0.25%) and maximum in April (6.15%). Between April and May, the histological dissection indicated presence of mature oocytes and oocytes undergoing resorption. Egg extrusion took place in mid April. During the summer months, the volume of oocytes gradually decreased. In winter and spring, the volume of oocytes began to increase during preparation for egg extrusion. The size of oocytes in the ovary increased from 0.2 mm at the beginning of the reproductive cycle to 1.8 mm immediately before egg extrusion. Average number of eggs in the ovary was 140.8 ± 51.63 (76-290). The ovary was of brown colour for the majority of the cycle, but white in June and July and orange in August and September. Mating started in October and continued through the winter. A difference was found in the proportions of testis and vas deferens in the male reproductive organ during the year. The male gonadosomatic index increased in September during preparation for mating (IG = 0.79%). During the mating season, the male spermatophores were predominantly filled with spermatozoa and sperm was also noted in the vas deferens. Two out of 15 males sampled during the winter were found to be intersex, in which atretic oogonia and oocytes were present at the periphery of testicular tissue and occupied less than 15% of testicular tissue. The evidence of intersex strongly suggested transitional stages of a gradual change of sex, which may be qualified as partial hermaphroditism.

한국 동해 해역에서 채집된 살오징어 (Todarodes pacificus)의 성성숙과 생식주기

The sexual maturity and reproductive cycle of the common squid, Todarodes pacificus captured from the East Sea, Korea, between January 2004 and January 2006, were investigated by documenting changes in the gonadosomatic index (GSI), gonad development, and oocyte size frequency distribution. The GSI of females began to increase in July, reached a maximum in August, and then gradually decreased. The GSI of males increased from July to March. Using gonad histological observations, we identified four oocyte developmental stages. The changes in GSI and gonad tissue resulted in the classification of the annual reproductive cycle into the following four successive stages: immature (April to June), growing (June to July), mature (July to August), and ripe and spawning (August to March). According to the oocyte diameter size frequency distribution in the ovary, this species appeared to have asynchronous oocyte development and one spawning time.