Mean Gonadosomatic Index Research Articles

Reproduction and growth of the spiny lebbeid shrimp, Lebbeus groenlandicus (Fabricius, 1775) (Caridea, Hippolytidae) in the East Sea of Korea

Reproduction and growth of the spiny lebbeid shrimp, Lebbeus groenlandicus (Fabricius, 1775), were investigated based on samples in the East Sea of Korea [= Sea of Japan], from January 2012 to April 2013. We collected 2964 shrimp samples during the study period, which included significantly more females than males (male : female ratio, 1.0 : 1.17). The females were generally larger than the males, and significant differences in the linear-regression slopes of carapace length (CL) versus body weight between the sexes indicate sex-specific differences in allometric growth. The gonadosomatic index (GSI) varied monthly, reaching a maximum in November 2012 (10.28) and a minimum in March 2013 (2.15). The proportion of ovigerous females varied from month to month. The highest values of the GSI coincided with the breeding period, and there was a significant difference between the mean GSI of females with non-eyed and those with eyed eggs, indicating that L. groenlandicus is a consecutive breeder. There was a significant correlation between CL and the number of eggs (EN) in the early egg stages. There was also a significant difference in the slopes of the regressions of CL versus EN between females carrying non-eyed and eyed egg stages. Based on the dry weights in the early egg stages, reproductive output was determined to be 0.18 ± 0.006. The Von Bertalanffy growth function parameters were CL∞ = 38.80 mm, year−1, , and WP = 0.4 for males, and CL∞ = 43.64 mm, year−1, , and WP = 0.6 for females. The growth performance index () was 2.86 for males and 2.89 for females.

Reproductive ecology of the female pink cusk-eel (Genypterus blacodes): evaluating differences between fishery management zones in the Chilean austral zone

The pink cusk-eel (Genypterus blacodes), a benthic-demersal fish confined to the southern hemisphere, supports an important commercial fishery in Chile where it is exploited over an extensive geographic area. Although the fishery was originally divided into a northern (41o28′–47o00′S) and southern (47o00′–57o00′S) zone for the purposes of fisheries management, recent studies have reported significant differences in life history parameters between these zones. Individuals from the southern zone reached larger asymptotic sizes and possessed higher survival rates compared to the northern zone. We estimate and compare the gonadosomatic index (GSI), shape of the maturity ogive, and length at 50 % maturity (L50%) of female G. blacodes between management zones and across time using biological data collected from the industrial fleet between 1985 and 2009. Females in the northern zone had higher monthly mean GSI than females in the southern zone. Our analyses also revealed L50% to be significantly higher in the southern zone than in the northern zone from 1985 to 2009. The significant differences in life-history traits between fishery management zones agree with the trade-offs predicted by Charnov’s life history theory. Together these results provide additional support for the hypothesis that two separate stocks exist and suggest that females from the northern zone have developed a life-history strategy, which favours early maturation and a proportionally greater investment in reproduction than females from the southern zone.

Reproductive biology of Benthosema pterotum (Teleostei: Myctophidae) in the shelf region of the East China Sea

Benthosema pterotum is a dominant myctophid in the shelf region of the East China Sea (ECS). They are a key species linking secondary producers and upper trophic levels. We examined the reproductive biology of B. pterotum in the ECS, based on 3065 specimens (10.7–54.8 mm standard length (SL)) sampled during cruises in 1999 and 2004–2009 to enable data over a 12 month cycle to be assessed. Between 14 and 30 mm SL, the ratio of females to males was ~1:1; it increased with SL, and all individuals ≥46 mm SL were females. The gonadosomatic index (GSI) at 50% sexual maturity of females and males was 3.91 and 0.24, respectively. Based on this criterion, females and males can mature at sizes larger than 28 mm and 24 mm SL, respectively. Although mature females having GSI ≥3.91 occurred over nine months (May–January), mean GSI of females peaked sharply during August–September, i.e. the primary spawning period. The hepatosomatic index peaked during April–July, and declined during August–September, indicating storage of materials and energy for reproduction. Based on data from seasonal bottom trawl surveys, small individuals of B. pterotum began to occur abundantly in autumn, and modal body lengths increased progressively during spring–summer, corresponding to the above reproductive seasonality. Oocytes at various sizes were found in mature ovaries, indicating that they are multiple spawners. Egg size at hydration ranged from 0.5 to 0.85 mm. Batch fecundity was positively correlated with SL, and ranged from 253 to 1942 eggs in fish from 30.1–54.8 mm SL.

Estimation of the Fecundity of Jat Puti, Puntius sophore (Hamilton)

The fecundity of 100 gravid female fishes of Jat puti, Puntius sophore, was collected from the experimental ponds of the Field Laboratory Complex, Faculty of Fisheries, Bangladesh Agricultural University (BAU), Mymensingh was estimated during the period from June to August 2011. Collected samples were clustered month-wise: group A (collected in June), group B (collected in July) and group C (collected in August). The estimated fecundity ranged of 7951 to 17670; 8135 to 23053 and 12461 to 15105 eggs and the mean gonadosomatic index (GSI) of 23.44 ± 2.50; 30.47 ± 4.52 and 28.43 ± 2.99 was estimated for the fish group of A, B, and C, respectively. The relationship between fecundity and total length was linear and it was expressed as: Ln F= 1634 ln TL-1972; Ln F= 119405 ln TL-273.53 and Ln F= 1831.6 ln TL+ 825.31 in group A, B, and C, respectively. The regression equation between body weight and total length was linear and it was expressed as: Ln W= 2.2128 ln TL- 0.7048; Ln W= 2.0207 ln TL+ 0.3493 and Ln W= 1.4438 ln TL+ 5.5694, in group A, B, and C, respectively. The regression equation between body weight and fecundity was linear and it was expressed as: F= 656.84 W+199.96, F= 438.16 W+2470, F= 1116.1 W-3433.5, in group A, B, and C, respectively. The fecundity was highly correlated with the total length, and body weight and P. sophore may be a medium fecund fish.DOI: http://dx.doi.org/10.3329/jesnr.v5i2.14833 J. Environ. Sci. & Natural Resources, 5(2): 295-300 2012

Reproductive Biology of Feather Back, Chital (Notopterus chitala, Ham.) Cultured in a Pond of Bangladesh

Studies on Gonadosomatic index (GSI), ova diameter and histology of the gonad were performed to understand reproductive biology of Feather back, Chital (Notopterus chitala) for a period of 6 months from January to June 2010. Thirty live chital fish were used in this study. The mean GSI values for female chital were found to range between 0.20±0.013 and 4.63±0.50. The highest GSI value was found in June. The smallest diameter of ovum was recorded 0.04 mm (January) and the largest was 4.00 mm (June). During the experimental period, the fecundity was ranged from 8,238 to 18,569 (mean 13,052±4607) in fish samples with body weight range from 1,296 to 2,360 (mean 1,742.50±474.44 g) while the relative fecundity was 5.65 to 14.33. Histological study revealed that the percentage of late perinucleolus (LPN) stage was highest in April and Cortical alveoli (CA) stage appeared from April and reached to maximum in May. Vitellogenic stage (VG) appeared in the month of May and chronologically increased through June. Vitellogenic stage (VG) of oocyte as well as highest ova diameter reached to the peak in June. The variations in the gonad weight and GSI of the female fish reached to the peak during June indicating maturity of ovary and definite spawning season. DOI: http://dx.doi.org/10.3329/ijarit.v2i1.13991 Int. J. Agril. Res. Innov. & Tech. 2 (1): 26-31, June, 2012

The influence of discharge, photoperiod, and temperature on the reproductive ecology of cyprinids in the Paluxy River, Texas

The distributions and abundances of cyprinids in North America are declining at an alarming rate with almost half of all known species considered imperiled and in need of conservation. Much of this loss in biodiversity is a result of flow regulation and climate change, especially in streams in the southern Great Plains that are prone to large and rapid fluctuations in discharge. The overall objective of this study was to examine the influence of discharge, photoperiod, and temperature on the reproductive ecology of cyprinids in the Paluxy River, Texas. Our results support previous findings in that photoperiod and water temperature were influential in the initiation and termination of the annual reproductive season. Interannual differences in GSI for Cyprinella venusta and Notropis volucellus indicated that reproductive effort in certain cyprinids was directly linked to discharge. In 2010, mean gonadosomatic index values for C. venusta (9.60 %) and N. volucellus (9.15 %) were at least twice that of 2011 (4.61 and 3.14 %, respectively); discharge during the spawning season of 2010 averaged 1,965 cfs, whereas it averaged only 177 cfs in 2011. Indeed, yearly differences in streamflow (i.e., mean annual discharge) can significantly impact the production of ova in a variety of cyprinids, even those non-broadcast-spawning species such as C. venusta. Consequently, we suggest conservation efforts should focus on maintaining natural flow regimes to combat the overwhelming loss of cyprinid diversity, especially as water extraction and climate change continue to threaten the biodiversity of freshwater fishes.

Dynamics of ovarian maturation during the reproductive cycle of Metynnis maculatus, a reservoir invasive fish species (Teleostei: Characiformes)

In this study, we evaluated the dynamics of ovarian maturation and the spawning processes during the reproductive cycle of Metynnis maculatus. Adult females (n = 36) were collected bimonthly between April 2010 and March 2011. The mean gonadosomatic index (GSI) was determined, ovarian and blood samples were submitted for morphometric evaluation and the steroid plasma concentration was determined by ELISA. This species demonstrated asynchronous ovarian development with multiple spawns. This study revealed that, although defined as a multiple spawning species, the ovaries of M. maculatus have a pattern of development with a predominance of vitellogenesis between April and August and have an intensification in spawning in September; in October, a drop in the mean GSI values occurred, and the highest frequencies of post-ovulatory follicles (POFs) were observed. We observed a positive correlation between the POF and the levels of 17α-hydroxyprogesterone. Metynnis maculatus has the potential to be used as a source of pituitary tissue for the preparation of crude extracts for hormonal induction; the theoretical period for use is from September to December, but specific studies to determine the feasibility of this approach must be conducted.

Effect of 17 a-Methyl Testosterone on Haematology and Histology of Liver and Heart of Oreochromis andersonii (Castelnau, 1861)

The aim of the study was to investigate the effect of 17 α-methyl testosterone (MT) on haematology and histology of liver and heart of Oreochromis andersonii subjected to varying levels of MT. Three different doses (40, 60 and 90 mgMT/kg feed) of MT were administered to O. andersonii. Final mean weight (g), gonadosomatic, cardiosomatic and hepatosomatic indices did not differ (P>0.05) among the treatments. Similarly, survival of the O. andersonii in all the treatments did not differ (P>0.05) significantly. Of the haematological and blood chemistry parameters determined, only haemoglobin (Hb), red blood cells (RBC), haematocrit and uric acid were significantly different (P<0.05), among the treatments with the control group having the highest of the latter two parameters. Haemoglobin (r=-0.743; P<0.05) and Red Blood Cells (RBC) (r=-0.726; P<0.05) showed significant association with MT levels. All the treatments did not show any histopathological differences in the liver and heart. However, all the liver samples showed haemosidrein (HE) and extra–hepatic pancreas (EH), while the heart exhibited the vacuolar degeneration (VD). The length–weight relationship coefficient differed (P<0.05) among the treatments with the fish fed with 40 mgMT/kg having the highest slope (2.642), although it only differed (P<0.05) with that of 90 mgMT/kg (1.547), which exhibited the worst condition. The study shows that the oral administration of MT for a short period of up to thirty (30) days does not affect the physiology of O. andersonii. Furthermore, the safety of MT to O. andersonii is, therefore, proved under the conditions of the current experiment. However, there are signs of condition deterioration in high levels of MT.

Maturation characteristics and life-history strategies of the Pacific lamprey, Entosphenus tridentatus

Lampreys (Petromyzontiformes) have persisted over millennia and now suffer a recent decline in abundance. Complex life histories may have factored in their persistence; anthropogenic perturbations in their demise. The complexity of life histories of lampreys is not understood, particularly for the anadromous Pacific lamprey, Entosphenus tridentatus Gairdner, 1836. Our goals were to describe the maturation timing and associated characteristics of adult Pacific lamprey, and to test the null hypothesis that different life histories do not exist. Females exhibited early vitellogenesis – early maturation stages; males exhibited spermatogonia – spermatozoa. Cluster analyses revealed an “immature” group and a “maturing–mature” group for each sex. We found statistically significant differences between these groups in the relationships between (i) body mass and total length in males; (ii) Fulton’s condition factor and liver lipids in males; (iii) the gonadosomatic index (GSI) and liver lipids in females; (iv) GSI and total length in females; (v) mean oocyte diameter and liver lipids; and (vi) mean oocyte diameter and GSI. We found no significant difference between the groups in the relationship of muscle lipids and body mass. Our analyses support rejection of the hypothesis of a single life history. We found evidence for an “ocean-maturing” life history that would likely spawn within several weeks of entering fresh water, in addition to the formerly recognized life history of spending 1 year in fresh water prior to spawning—the “stream-maturing” life history. Late maturity, semelparity, and high fecundity suggest that Pacific lamprey capitalize on infrequent opportunities for reproduction in highly variable environments.

Reproductive Strategy ofLabeobarbus batesii(Boulenger, 1903) (Teleostei: Cyprinidae) in the Mbô Floodplain Rivers of Cameroon

Aspects of the reproductive strategy of African carp,Labeobarbus batesii, were investigated from May 2008 to October 2009 in the Mbô Floodplain of Cameroon. Samples were collected monthly from artisanal fishermen. The total length and total body mass of each specimen were measured to the nearest mm and 0.01 g, respectively. Sex was determined by macroscopic examination of the gonads after dissection. The sex ratio was female skewed (overall sex ratio: 1 : 1.42). Females reach sexual maturity at a larger size (213 mm) than the males (203 mm). The mean gonadosomatic index ranges from0.32±0.17% to1.91±1.15%, whereas the meanKfactor ranges from0.90±1.09to1.10±0.13. These two parameters are negatively correlated. The reproduction cycle begins in mid-September and ends in July of the next year, and they are reproductively quiescent for the rest of the year.Labeobarbus batesiiis a group-synchronous spawner with pulses of synchronised reproduction spread over a long period. The mean absolute, potential, and relative fecundities are2898±2837oocytes,1016±963oocytes, and9071±7184oocytes/kg, respectively. The fecundity is higher and positively correlated with the gonad mass than with body size. Its reproductive biology suggests thatL. batesiiis suitable for pond culture.

Reproductive traits of the lake prawn Palaemon paucidens De Haan, 1844 (Decapoda, Palaemonidae), from Goesan Lake, South Korea

The reproductive biology of Palaemon paucidens De Haan, 1844, from Goesan Lake, Korea, was investigated during the period May 2010-October 2011. The proportion of females was significantly greater than that of males (female : male ratio, 1 : 0.7). The gonadosomatic index (GSI) varied monthly, reaching a maximum in May and a minimum in September. Monthly variations in the proportions of ovigerous females showed peaks in April and May. The highest values of the GSI coincided with the breeding period of P. paucidens (April-August). There was no significant difference between the mean GSI of females with non-eyed and eyed eggs, indicating that P. paucidens is a non-consecutive breeder. There was a significant correlation between the number of eggs and the carapace length at early egg stages. There was no significant difference in the intercepts of the regressions of the number of eggs versus carapace length between females carrying non-eyed and eyed egg stages, indicating that there was no brood loss during the incubation period. Egg volume increased significantly (by 75.6%) as eggs developed from the non-eyed to the eyed stage. Reproductive output was 0.20 ± 0.04, based on dry weights in early egg stages. The results were compared with other studies of P. paucidens in Sukdang Lake and other species of palaemonids in different habitats. This comparison reveals intra- and inter-specific variations in reproductive traits of palaemonid shrimp. The phenomenon is suggested to be a result of adaptations to different environmental conditions. Variation in reproductive traits within the same species reflects a different life strategy adaptation in species that will require a different approach in fisheries management. Information on intra- and inter-specific variation in reproductive traits is important to be used as one basic issue of biological information to support an effective fisheries management of P. paucidens, which has been locally exploited in Korea and Japan.

Development of an Immunological Probe to Quantify Reproductive Effort in the Suminoe Oyster,Crassostrea ariakensis(Gould 1861)

A polyclonal antibody specific to an egg protein of the Suminoe oyster, Crassostrea ariakensis, was developed to assess reproductive effort. After 2 mo of immunization, rabbit antiserum showed strong specificity to the egg protein in an enzyme-linked immunosorbent assay (ELISA). The rabbit antioyster egg immunoglobulin G detected as little as 0.2 µg/mL of Suminoe oyster egg protein by ELISA. The quantity of eggs present in an oyster was estimated using ELISA and was expressed as a gonadosomatic index (GSI). Gonadosomatic index values of Suminoe oysters were assessed monthly from January to July 2007 at the Seomjin River estuary off the south coast of Korea. Histology indicated that most oysters were mature and ready to spawn by the middle of July. Mean GSI values for oysters collected in April, when most female oysters are in early developmental stages, varied between 0.6% and 14.0%. In July, most oysters were ready to spawn and GSI values ranged from 17.5–67.0%, with a mean of 47.7%. The potential fecundity of ripe oysters was determined by dividing the number of eggs, which was estimated by ELISA, by the mean dry weight of a single egg (14 ng); fecundity ranged from 162–910 million eggs. The immunological technique used in this study was affordable and sensitive enough to measure variation in the number of eggs present among gametogenic stages.

Reproduction of the Brazilian snapper, Lutjanus alexandrei Moura &amp; Lindeman, 2007 (Perciformes: Lutjanidae), off the northern coast of Pernambuco, Brazil

Reproductive aspects of the Brazilian snapper Lutjanus alexandrei, were characterized, including a description of the development of oocytes and spermatogenic cells, size at first sexual maturity, and fecundity. A total of 540 fish were analyzed with 250 having their gonads sectioned to allow microscopic evaluation. Six maturity stages were identified for females and males: immature, maturing, mature, spawning, spawned, and resting. Fish standard length (SL) varied from 13.0 to 28.3 cm and sex ratio was 1.6 males: 1.0 females. Monthly distributions of mean Gonadosomatic Index (GSI) and maturity stages suggest that spawning occurs mainly in a protracted period, during the warmer months, from November to March. The size of first sexual maturity was estimated at 17.1 cm SL for females and 16.8 cm SL for males. Oocyte development suggests that L. alexandrei exhibits a multiple batch spawning behavior and batch fecundity varied from 34,000 to 324,000 oocytes.

Management of crown-of-thorns sea star (Acanthaster planci L.) outbreaks: Removal success depends on reef topography and timing within the reproduction cycle

Removals of crown-of-thorns sea stars (Acanthaster planci L.) are crucial initiatives in limiting the damage to coral reefs during outbreaks, but have often been unable to control the populations. We hypothesized that reef topography and exact timing of removals (before reproduction) determine their success and studied these in reefs along the western shore of Samal Island in the Philippines.An outbreak of A. planci was successfully removed from an isolated reef (surrounding water column >40 m) during 42 dive hours. In August 2009, the removal rate was initially 14 specimens h−1, which sharply decreased to less than 4 h−1 after the third removal. From May 2011 onward, no specimens were observed. All sea stars were found at depths ≤18 m, which confirmed that migration to isolated reefs is very unlikely. Mean gonado-somatic index (GSI) ranged from 6 to 15 in April–May 2010 and March–April 2011. During the rest of the year, mean GSI ranged between 0 and 4. Maximum GSI of 22.0 was found for one female specimen in April 2010. Maturation occurred at a diameter of 13 cm (female) and 16 cm (male). Diameter frequency distributions showed a new cohort (7 ≤ diameter ≤ 10 cm) between November 2009 and February 2010. To accurately compare results of various studies, relationships between underwater diameter, surface diameter, and crown-of-thorns weight, were established. Removals are recommended to be performed in isolated reefs, where migration from adjacent areas is limited, and before reproduction in April (Northern hemisphere), reducing the chance of future outbreaks.

REPRODUCTION BIOLOGY OF CHUB LIVING IN LAKE HAFIK

In this study, the reproductive biology of chub population in Hafik Lake was investigated. 242 samples were caught between April and November 2009. The age of S. cephalus samples were found to range between I-VIII; in addition, 153 of them were female and 89 were male. Their fork lengths changed between 114-332 mm, and body weights were between 22.5 and 550.3 g. Male specimens were determined to reach sexual maturity at II and III age, while females reached at III and IV years of age. The smallest female individual at sexual maturity had 114 mm of fork length and 27.3 g, while the smallest male at sexual maturity had 118 mm of fork length and 24.2 g. The mean gonadosomatic index of male and female specimens were found highest in April (12.33, 8.02) and May (8.37, 4.64) and minimum in August (2.39, 1.22). Egg diameters of chub individuals were measured between 343 µm and 1900 µm. The egg number in per one gram ovary was maximum in August, and minimum in April and May. S. cephalus was determined to lay eggs in Hafik Lake towards the end of April, which continued until the end of July. Maximum fecundity in population was observed as 151302 in the specimen at the age of VI.

Localised spawning omission in snapper, Chrysophrys auratus (Sparidae)

Failure to spawn in a significant proportion of adult fish may greatly decrease the reproductive output of a population and lead to overestimates of recruitment to the fish stock. Reproductive output of the commercially important sparid, Chrysophrys auratus, around the Kaipara Harbour, New Zealand, is particularly important as this harbour is the primary source for the C. auratus population along the west coast of the North Island of New Zealand. We tested the hypothesis that C. auratus do not spawn inside the Kaipara Harbour by comparing monthly gonad and otolith samples from fish caught within the harbour with those of fish from surrounding coastal waters. Fish from coastal waters showed normal gonad development with peak spawning in spring. By comparison, almost all adult fish from the harbour had underdeveloped gonads, with mean gonadosomatic indices ≤1. Histological gonad analyses of C. auratus caught in the harbour showed vitellogenic oocytes were reabsorbed before spawning. Therefore, recruitment to the harbour must originate from spawning that occurs outside the harbour. This first record of spawning omission in C. auratus has important implications for fisheries management, as it may lead to overestimation of the spawning stock and increase the risk of broad-scale population depletion, through the targeted fishing of spawning aggregations.

Ovarian development of a river catfish Hemibagrus nemurus (Valenciennes, 1840) in captivity

Hemibagrus nemurus is a riverine catfish with high economic and nutritive values. Investigations on ovarian development of this fish were carried out to determine the mode of ovarian development and describe the oocyte developmental stages. Histological studies were done on ovaries using light microscopy and scanning electron microscopy. Fish were sampled monthly for a period of six months (August 2009 to January 2010). The mean oocyte diameter (OD) ranged from 871 ± 161.41 µm to 1,167 ± 26.77 µm and the highest OD was in November. Oocyte size-frequency distribution showed a polymodal distribution. The mean gonadosomatic index (GSI) ranged from 1.14 ± 0.87% to 7.06 ± 1.40% and highest GSI was in November. The ovaries exhibited three phases of oocyte growth, which were primary growth, secondary growth and maturation phases. Based on histological criteria, the oocyte developmental stages were divided into seven stages as chromatin nucleolar, early perinucleolar, late perinucleolar, cortical alveolar, vitellogenesis, mature oocyte and germinal vesicle migration stages. All the seven stages of oocyte development were observed in the ovaries. Oogonia were always present throughout the developmental stages. The ovaries had more than two stages of oocyte development. This is the first report on the mode of ovarian development of H. nemurus. These findings indicated that H. nemurus has asynchronous mode of ovarian development and is capable of spawning several times in a year under favourable conditions.

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%.

Biology and invasive potential of the introduced swordtail Xiphophorus hellerii Heckel (Poeciliidae) in Western Australia

Abstract The swordtail Xiphophorus hellerii is a popular ornamental freshwater fish that occurs as an introduced species in the aquatic habitats of at least 31 countries. Although introduced populations are found in other Australian states, the only known Western Australian population occurs in the Irwin River (29°15′S). The biology of X. hellerii in the Irwin River in south‐western Australia is described from four seasonal samples, collected by seine net, between spring 2002 and winter 2003. Pregnant females were collected in all seasonal samples, though juveniles were absent in spring, implying that juvenile mortality during late winter is high. Although mean length of pregnant females (38.7 mm) and mean gonadosomatic index (GSI) (14.7) were similar to reported data for X. hellerii populations in Queensland, mean fecundity was markedly lower in Western Australia, i.e. 34.1, cf. 60.15. Logistic analysis of the percentage of female and male X. hellerii with developing and mature gonads predicted that the length at which 50% of the sexes mature was 30.8 and 31.5 mm SL, respectively. The sex ratios of females to males did not differ statistically from a ratio of 2:1. The diet of all X. hellerii size classes was omnivorous (primarily vegetal matter/algae), although a significant difference was observed between the diet of juveniles and that of the two larger size classes (i.e. juveniles consumed greater quantities of aquatic invertebrates). A melanic polymorphism (i.e. pigmented caudal peduncle and fin) was observed in approximately 5% of X. hellerii collected. If released, the range of X. hellerii is likely to expand in anthropogenically modified habitats in tropical and temperate latitudes of Western Australia. Potential ecological impacts on indigenous fishes may be magnified owing to the depauperate nature of the endemic ichthyofauna including a lack of predators. Copyright © 2011 John Wiley &amp; Sons, Ltd.

The stimulatory effects of long wavelengths of light on the ovarian development in the tropical damselfish, Chrysiptera cyanea

The sapphire devil, Chrysiptera cyanea, were reared for 45 days during the non-reproductive season (September) under LD14:10 at four different wavelengths produced by light emitting diodes (LEDs): red (peak at 627 nm), green (530 nm), blue (455 nm) and white (5000 K). Ovarian maturation occurred in fish exposed to red, green and blue light, but not to fish under either white or natural light (control group). Mean gonadosomatic index was higher ( P < 0.05) in fish group reared under red light than those reared under other treatments. Moreover, the ovaries of all fish (10/10) reared under red LED light contained vitellogenic oocytes. By contrast, a few fish in the groups of green LED (4/10 individuals) and blue LED (2/10 individuals) contained vitellogenic oocytes in ovaries, while the fish in the white LED and control groups had oocytes at immature stages. These results indicate that the light wavelength influences ovarian development in the sapphire devil and the level of effectiveness was red light > green light > blue light. The present results demonstrate that in addition to photoperiod, light wavelength is important for induction of gonadal maturation of reef fishes and that LED becomes a useful tool for aquaculture. Since responsiveness to lighting environments may differ among species, it is necessary to define optimum photic conditions on a species by species basis, if an artificial induction of reproduction is conducted by lighting environment in fish.