Aspects of the reproductive biology of two archer fishes <Emphasis Type="Italic">Toxotes chatareus</Emphasis>, (Hamilton 1822) and <Emphasis Type="Italic">Toxotes jaculatrix</Emphasis> (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.     

Reproductive biology of Hemiramphus brasiliensis and H. balao (hemiramphidae): maturation,spawning frequency,and fecundity

Analyses of life-history data show that both the size-specific batch fecundities and the age-specific spawning frequencies differ for two halfbeak species, Hemiramphus brasiliensis, the ballyhoo, and H. balao, the balao. Halfbeak ages were determined from sectioned otoliths; histological data was used to describe oocyte development and estimate spawning frequency; and batch fecundity was measured from counts of whole oocytes in final maturation. Hemiramphus brasiliensis lived longer (4 versus 2 years) and had a higher survival rate (14.9% versus 7.5% annually) than H. balao did. Of the two species the larger and longer-lived congener, H. brasiliensis, reached sexual maturity at a larger size (fork length 198 versus 160 mm). The spawning period of age-0 females was strongly related to season, whereas spawning by older females occurred throughout the year. Reproduction by both species peaked during late spring or early summer, and all mature females were spawning daily during April (H. brasiliensis) or June (H. balao). This is the first demonstration of iteroparity for the family Hemiramphidae. H. brasiliensis had a lower batch fecundity (about 1164 versus 3743 hydrated oocytes for a 100-g female) than H. balao did. Such low batch fecundities are typical of the order Beloniformes, but quite different from those of other fishes that live in association with coral reef habitats. H. balao's higher batch fecundity is consistent with the life-history theory that predicts higher numbers of eggs for shorter-lived species; this is possible because H. balao produces smaller hydrated oocytes than H. brasiliensis (modal diameter about 1.6 versus 2.4 mm). The high spawning frequency of Hemiramphus species compensates for their low batch fecundity. The annual fecundity of both species is similar to that of other reef fish species, after adjusting for body size and spawning frequency. The lifetime fecundity of H. balao was very similar to that of H. brasiliensis, after accounting for the differences in survival for each species. This suggests a fine tuning of different reproductive traits over the entire life cycle that results in roughly equivalent lifetime fecundity for both species.     

Reproductive strategy of Leporinus piau (Fowler, 1941), a neotropical freshwater fish from the semi‐arid region of Brazil

This study concerns the reproductive strategy of the freshwater fish, Leporinus piau, native to the Brazilian semi‐arid region. The hypothesis of this work predicts that the species would spawn during the rainy season, presenting a seasonal reproductive strategy. The study investigated the structure of total body length and body mass, sex ratio, body size at first sexual maturity, developmental stages of gonads, fecundity, gonadosomatic index (GSI), condition factor (K) and the spawning season of L. piau. Twelve monthly samplings (mean n = 18) were carried out in 2009 and environmental parameters such as rainfall, temperature, pH, electrical conductivity and concentration of dissolved oxygen of water were registered. The sampled population of L. piau (n = 211) showed a slight predominance of males (55%), but with larger and heavier females. First sexual maturation in males occurred earlier (16.5 cm total length) than in females (20.5 cm total length). The species is a total spawner with an average fecundity of 55 000 mature oocytes. Rainfall (225 ± 7.2 mm) and concentration of dissolved oxygen (8.5 ± 0.2 mg L^?1) acted as influential factors during the spawning season. The monthly GSI shows that spawning starts when the rainy season is at its maximum and ends synchronously (females r = 0.91; males r = 0.89) with the end of the rainy season. L. piau presents a seasonal reproductive strategy with high reproductive output, providing a population increase and exploitation of the environmental resources.     

Reproductive strategy of Psectrogaster rhomboides Eigenmann & Eigenmann, 1889, a freshwater fish from Northeastern Brazil

Several environmental parameters related to the spawning season of the freshwater fish, Psectrogaster rhomboides were identified. The hypothesis predicts synchrony of the spawning season with the rainy period, presenting a seasonal reproductive strategy. This study investigated the total body length and body mass, sex ratio, body size at first sexual maturity, gonadosomatic index, condition factor, fecundity and reproductive period of P. rhomboides in the natural environment. Twelve monthly samplings (mean n = 20) were carried out from March 2009 to February 2010. Fish were captured using 4 cm diameter cast nets and environmental parameters such as rainfall, temperature, dissolved oxygen concentration, pH and electrical conductivity of the water were registered. The sampled population of P. rhomboides (n = 444) showed a sex ratio of 1 : 1. Females attained first sexual maturity at 15 cm total length and males at 15.3 cm total length. Spawning occurred from March to May, with high gonadosomatic index values during the rainy season. This species is a total spawner, with a mean fecundity of 6188 (±367) mature oocytes. P. rhomboides presents a seasonal reproductive strategy, providing a population increase and exploitation of the environmental resources during the rainy period. Rainfall (196.5 ± 4.9 mm) and the concentration of dissolved oxygen (7.82 ± 0.7018 mg L^?1) were influential factors during the spawning season. Gonadosomatic index and the condition factor were negatively correlated during the gonadal development cycle of this species. The monthly gonadosomatic index values show that spawning begins when the rainy season is at its maximum and ends synchronously (females r = 0.9171; males r = 0.889) with the end of the rainy season.     

Comparative fecundity and oocyte size of Aristaeomorpha foliacea and Aristeus antennatus in the Greek Ionian Sea (E. Mediterranean) (Decapoda: Aristeidae)

Absolute and relative fecundity of 49 ripe gonads (from the cephalic and the abdominal sections of the same specimen) of Aristaeomorpha foliacea and 71 ripe gonads of Aristeus antennatus caught in the Ionian Sea (E. Mediterranean) and their oocyte size were studied. Both average absolute and relative fecundities estimated for A. antennatus were statistically higher than those estimated for A. foliacea; the average absolute fecundity of A. foliacea was 151 936 oocytes/female and that of A. antennatus was 200 472 oocytes/female and the average relative fecundity of A. foliacea was 5477 oocytes/g and that of A. antennatus was 9386 oocytes/g. Fecundity in both red shrimp species is linearly related to carapace length, body and gonad weight, although, the most precise estimation is provided by the relationship of body weight and fecundity. In the present study, the oocyte size (diameter, volume) of both species could be considered very large. In conclusion, A. foliacea shows lower fecundity than A. antennatus, having a lower ovogenetic activity, but it produces larger oocytes. This is in accordance with the highest value of the gonad weight and gonad volume of A. foliacea exhibited in relation to A. antennatus.     

Age, growth and fecundity of the silver mullet, Mugil curema (Pisces: Mugilidae), in coastal areas of northeastern Venezuela

We studied fecundity and growth in populations of the silver mullet, Mugilcurema, in coastal areas of northeastern Venezuela between March 1992 and July 1993. The average number of oocytes in gonads of 23-42 cm adults was 54 x 10(4), and the relative fecundity was 1,311 oocytes g-1 of fish. The size of mature oocytes did not vary in different portions of the same gonad (p > 0.05) or among the adults in three populations studied. The average egg diameter for adults was 426 microns (CI = 4.34). Age of juveniles, collected from the La Restinga Lagoon at about monthly intervals, from counts of growth lines on the otoliths ranged from 50 to 240 days. The relation of age (number of growth lines) to standard length follows an exponential growth curve. The growth of juveniles varied seasonally and was greatest during the rainy season (April to August), when temperatures were highest. The time of spawning has probably been adapted so that peak recruitment into the lagoons occurs just prior to the rainy season when conditions for growth are most favorable.     

Reproductive strategies of a temperate Australian sciaenid (teraglin,Atractoscion atelodus)

Worldwide there have been declines in stocks of exploited sciaenids. Despite a long history of exploitation, there has been no study of the life history characteristics of the fishery-important sciaenid, teraglin, Atractoscion atelodus. This study describes the reproductive characteristics of A. atelodus within the major area of its distribution and fishery, New South Wales (NSW) Australia. Characteristics studied included the size and age at maturity, fecundity, spawning mode and season, and these are compared to congeneric species. Atractoscion atelodus displays year-round batch spawning behaviour with asynchronous oocyte development and indeterminate fecundity. This is unusual for sciaenids, which typically display spring-summer spawning and only over a few months. The length and age at which 50% of the population matures for both males and females is 36 cm fork length (FL) and 1 year, a smaller size compared to other closely related sciaenids. While the species displays resilient reproductive characteristics such as protracted year-round spawning, constant supply of vitellogenic oocytes and relatively small/young age at maturity, there are also characteristics that make it susceptible to over-exploitation. These include highly female skewed sex ratios, as well as their schooling and voracious feeding behaviour leading to the potential for high catch rates.     

Reproductive biology of hardhead catfish Ariopsis felis: evidence for overwintering oocytes

Hardhead catfish Ariopsis felis are a common marine catfish in the coastal waters of the Gulf of Mexico (GOM). The low economic value of this species has depressed interest and research, and although the species is known for its extremely low fecundity and large oocytes, little else is known about this catfish species. A total of 1230 samples across all months of the year from 2016 to 2018 resulted in 681 females, and analysis of gonado-somatic index (I_G) revealed 1% to be a clear cut-off indicating maturity. Females are considered capable of spawning from April to June when I_G averaged 4–8%. Both atresia and post-ovulatory follicles were present in July, suggesting that spawning ends in July in the northern GOM. The 1% I_G cut-off was used to designate maturity, and from that an L₅₀ of 253 mm was estimated. Batch fecundity from 41 females estimated a mean batch size of 36 oocytes. Perhaps the most interesting finding was the presence of secondary growth stage oocytes (e.g., cortical alveoli) from July through November, well outside the spawning capable period. Furthermore, 78% of females had some early vitellogenic oocytes present during the non-spawning season, and the distribution of these relatively large (2–5 mm) oocytes did not change over time. The results here are not only important as reproductive biology information for a common and abundant species, but also present interesting and unusual patterns of non-spawning season oocyte development that is not commonly seen in Western Hemisphere subtropical fish species.     

Timecourse of oocyte development in saithe Pollachius virens

Wild caught North Sea saithe Pollachius virens were monitored for growth, sex steroid profiles and oocyte development pre‐spawning and measured for egg size and group fecundity during the spawning season in the laboratory. Vitellogenesis commenced in late October–early November, at a leading cohort size (C_L) of c. 250 µm, after which oocytes grew rapidly in size until spawning started in February. Notably, a distinct cortical alveoli stage was virtually absent with yolk granules observed in developing oocytes at the very beginning of vitellogenesis. Little atresia was observed pre‐spawning, but atretic re‐absorption of remnant oocytes containing yolk granules was found in all females immediately post‐spawning. As expected, concentrations of sex steroids, oestradiol‐17β (females), testosterone (both sexes) and 11‐ketotestosterone (both sexes), increased pre‐spawning before dropping post‐spawning. The present experiment provides the first validation of sex steroid levels in P. virens. Post‐ovulatory follicles were visible in histological sections from female gonads 9–11 months post‐spawning, but then disappeared. Spawning commenced around a C_L of c. 750 µm (700–800 µm). Hydrated oocytes (eggs) measured between 1·04 and 1·31 mm (mean = 1·18 mm) with decreasing sizes towards the end of spawning. The average estimated realized fecundity was c. 0·84 million eggs (median female total length, L_T = 60 cm). Spawning lasted from 13 February to 29 March.     

Comparative oocyte morphology and fecundity of five characid species from São Francisco River basin,Brazil

The morphology of vitellogenic oocytes and the batch fecundity of five tropical forage species belonging to the family Characidae, were studied in 104 late‐maturing ovaries. Significant morphological differences between vitellogenic oocytes and ovarian follicles were found. The lowest batch fecundity values were recorded in Hemigrammus marginatus (480 ± 163) and Orthospinus franciscensis (1701 ± 562), which were the smaller species in terms of total length, body weight and oocyte diameter. The highest batch fecundity value was observed in Tetragonopterus chalceus (8384 ± 3944) having the highest GSI and oocyte diameter. Batch fecundity and gonad weight was highly correlated followed by body weight and total length. Relative fecundity was estimated per unit total length, body weight and gonad weight. The wide variation in fecundity observed between the specimens and the species analysed is possibly related to the multiple spawning reproductive strategy of these fishes. Since T. chalceus have higher values of batch and relative fecundity, it is concluded that this species has a higher reproductive potential than the other forage species studied.     

Time course of oocyte development in winter flounder Pseudopleuronectes americanus and spawning seasonality for the Gulf of Maine,Georges Bank and southern New England stocks

Winter flounder Pseudopleuronectes americanus were collected at monthly intervals from December 2009 to May 2011, to describe the pattern and seasonality of oocyte development, including: (1) the group‐synchronous transition from primary to secondary oocytes that initiates immediately after spawning, (2) the slow (months) development of vitellogenic oocytes followed by the rapid (weeks) maturation of oocytes, (3) the synchronous nature of mature oocytes ovulating, but the discrete releases of benthic eggs in batches, (4) the protracted (months) degradation of postovulatory follicles and (5) the occurrence of follicular atresia. Although fish were collected across only c. 2° latitudinal range, the spawning season was c. 1 month later in the Gulf of Maine (GOM) than on Georges Bank and in southern New England. This is probably due to lower temperatures in the GOM. These stock‐specific data regarding the time course of oogenesis are of practical value. This information is discussed in relation to measuring and interpreting elements of reproductive potential such as maturation, skipped spawning and fecundity, the response of reproductive traits by this widely distributed species to changing climate and the response by this common, marine‐estuarine species to urbanization, particularly environmental pollutants and dredging.     

Batch fecundity and spawning frequency of invasive Hemiculter leucisculus (Basilewsky, 1855) in Erhai Lake,China

Hemiculter leucisculus are multiple spawners with indeterminate fecundity, although previous fecundity estimates have assumed a determinate spawning pattern. Batch fecundity and spawning frequency of H. leucisculus were studied in Erhai Lake, China, in which the fish, as an exotic species, has become a successful colonizer. Spawning frequency was 16.05 %, as determined from the percent of females with postovulatory follicles 12 to 36 h old during the peak reproductive period (from May 27 to August 8). The average interval between spawning was 6.2 days and there were more than 16 total spawning batches during the peak reproductive period. The average batch fecundity (mean ± SD) was 11,934?±?5,921 hydrated oocytes in 40 females (standard length or SL: 9.1–14.4 cm), while relative batch fecundity was 560?±?137 eggs g^?1 wet weight. The total potential annual fecundity was approximately 190,944 oocytes over the whole spawning season and was much higher than the estimated standing stock (31,585 oocytes) of yolked oocytes (36 females, SL: 9.5–16.2 cm) at the beginning of the spawning season in April 2010. This high annual fecundity is likely to have contributed to successful invasion of Erhai Lake by H. leucisculus.     

Reproductive biology of Melanophryniscus montevidensis (Anura: Bufonidae) from Uruguay: reproductive effort,fecundity, sex ratio and sexual size dimorphism

We analyzed the reproductive traits of a population of Melanophryniscus montevidensis. The reproductive events were associated to rainfalls. Males called from dawn to late night, were more abundant than females, and adopted alternative tactics to find partners (active search). Females were larger than males, and had mature oocytes and lipid reserves after spawning; they showed no association between size and fecundity. As an explosive breeder, females are prepared all year long for reproduction. Several individuals revealed high site-fidelity for breeding. Knowledge about breeding pattern could help to propose suitable and efficient in situ conservation measures for this endangered species.     

Goosefish Lophius americanus fecundity and spawning frequency,with implications for population reproductive potential

To improve knowledge of goosefish Lophius americanus' reproductive biology, females were collected during 2009–2012 from the Mid‐Atlantic Bight shelf region of the U.S. east coast. Batch fecundity increased with total length (L_T), from 229 100 to 2 243 300 mature oocytes per female (L_T range: 55·5–112 cm; n = 54). This estimate of fecundity at L_T is lower than one derived from a sample collected during 1982–1985. Examination of whole oocyte diameters in different months indicated that L. americanus is a serial spawner, releasing more than one egg veil per spawning season, as suspected or observed for other Lophius species. Seasonality of spawning was evident from whole oocytes and gonad histology, and from larval fish surveys spanning the U.S. north‐east shelf, and confirmed a protracted (c. 6 months) spawning period. Peak spawning activity progressed northward from spring to autumn. The population‐level implications of these results were explored by estimating population reproductive potential (P_RP), which considered the value of both current and future per capita reproduction using decade‐specific age structure and fecundity at length. P_RP is now more than 50% lower compared with the historical period (1982–1985), a result of the lower proportions of large females and reduced fecundity across all sizes. Mechanisms that could explain this loss of stock productivity are fishing‐induced size–age truncation or regime shifts in egg production caused by changes in energy density of common forage species.     

Aspects of the fecundity of the feral catfish,Clarias macrocephalus (Gunther), population obtained from the rice fields used for rice-fish farming,in Malaysia

The catfish, Clarias macrocephalus, harvested from the irrigated rice fields of Malaysia, exhibited spawning activities that are influenced by water level management. The multiple spawning potential of the fish is negated by declining water level and the fish spawned only once per growing season. Although oocyte development started in conjunction with water level increase, subsequent oocyte development did not take place due to low water level. Absolute and relative fecundity also decreased with declining water level, however, mean relative fecundity is relatively constant (17.6–53.7 oocytes g^–1 body weight) and not related to body size. Absolute fecundity ranged between 785 to 14066 oocytes female^–1, whereas relative fecundity is between 7.1 to 83.5 oocytes g^–1 body weight, respectively.     

The reproduction of Chaetodon austriacus,C. fasciatus and C. paucifasciatus (Chaetodontidae,Perciformes) in the Jordan Gulf of Aqaba

Synopsis Aspects of the reproduction of three sympatric and endemic chaetodontids, Chaetodon austriacus, C. fasciatus and C. paucifasciatus, from the Jordan Gulf of Aqaba were investigated. Chaetodon fasciatus had a higher fecundity than the other species which, in turn, had similar fecundities. The major egg release of C. austriacus and C. paucifasciatus began in August, that of C. fasciatus in September. Based on the gonadosomatic index of both sexes, the spawning period of C. austriacus was from July through October, that of C. paucifasciatus from August through October and that of C. fasciatus from September through December. The maturity length of the three chaetodontids is given and reproductive isolation among the sympatric species is discussed.     

Ovarian dynamics and fecundity regulation in blueback herring,Alosa aestivalis,from the Connecticut River,US

We analyzed ovarian dynamics of anadromous blueback herring, Alosa aestivalis, in Connecticut River with the principal aim of exploring oocyte recruitment and how it shapes the fecundity pattern. We examined the oocyte release strategy and analyzed spawning cyclicity by linking oocyte growth to the degeneration of postovulatory follicles. Females were accordingly classified as pre-spawners, early and late active spawners, and oocyte recruitment intensity was compared among the different spawning phases. Oocyte recruitment occurred continuously and in parallel with spawning activity, a pattern which is diagnostic of indeterminate fecundity. However, both fecundity and oocyte recruitment intensity progressively decreased (tapered) throughout spawning, until the ovary was depleted of vitellogenic oocytes. There was no massive atresia of vitellogenic oocytes at the end of the spawning season, which is atypical of indeterminate spawners. We propose that tapering in oocyte recruitment and fecundity is an adaptation to the high energetic expenditure of the upstream spawning migration.     

Reproductive biology of the armoured catfish Loricariichthys castaneus (Castelnau, 1855) in Lajes reservoir,southeastern Brazil

Sex ratio, gonadal development, breeding season and fecundity of the armoured catfish Loricariichthys castaneus were described to assess its reproductive strategy in a Brazilian tropical reservoir. In total, 226 specimens (199 females and 27 males) were captured from September 2005 to August 2006 and examined in the laboratory. Females outnumbered males and achieved sizes larger than 330 mm TL. Oocyte development, determined by histological analysis, was asynchronous with oocyte size, ranging from pre‐spawning (27–270 μm) to spawning (243–3460 μm), followed by a sharp decrease in the mean oocyte diameter postspawning (590–730 μm) as the spawning proceeded. Spawning occurred throughout most of the year, peaking in August–September and reaching a low in April–May, according to variations in GSI and frequencies of stages of gonadal development. Batch fecundity ranged from 242 to 833 vitellogenic oocytes (relative fecundity = 2.27 oocytes g^?1), averaging 483 oocytes, and was positively related to gonad weight (P = 0.00003). Oocyte diameters ranged from 0.027 to 5.59 mm, with vitellogenic diameters ranging from 2.08 to 5.59 mm. Continuous development of oocytes throughout the year suggests that L. castaneus presents indeterminate fecundity and is a batch‐spawner. These attributes, associated with parental care and a wide reproductive period, correspond to an equilibrium strategy that has proved to be effective in the Lajes reservoir.     

Reproductive strategies in female polar and deep-sea bobtail squid genera <Emphasis Type="Italic">Rossia</Emphasis> and <Emphasis Type="Italic">Neorossia</Emphasis> (Cephalopoda: Sepiolidae)

Female reproductive features have been investigated in five polar and deep-sea bobtail squid genera Rossia and Neorossia (R. macrosoma, R. moelleri, R. pacifica, N.c. caroli and N.c. jeannae). These species are characterized by asynchronous ovary maturation, very large eggs (>10% ML), fecundity of several hundred oocytes, very high reproductive output, and continuous spawning with low batch fecundity. This adaptive complex of reproductive traits evolved in these small animals as an optimum strategy for polar and deep-water habitats.