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.     

Reproductive strategy of the European perch,Perca fluviatilis Linnaeus, 1758 (Osteichthyes: Percidae) in the Anzali wetland,southwest Caspian Sea

Temporal variation in reproductive traits of geographically distributed fish is supposed to take place in response to the spatial and environmental variations. With regard to the wide distribution of the European perch in the northern hemisphere, important reproductive traits such as the initiation and duration of the spawning activity are likely to vary in different latitudinal gradients. In this study, reproductive biology of the European perch, Perca fluviatilis, is described, based on 324 specimens caught in the Anzali wetland (southwest Caspian Sea) between June 2008 and May 2009. The gonadosomatic index, oocyte frequency distribution and histological examination suggested a long vitellogenic process (October to February) and a short spawning season (January and February). The size‐frequency distribution of the oocytes showed that this perch is a species with group‐synchronous ovarian development. Ovarian development occurred only in one clutch of oocytes (700–900 μm oocyte diameter) with no indication of maturation of any subsequent clutch in the spawning season. The average of (realized) fecundity (±SD) was estimated to be 16177 ± 5846 eggs in late vitellogenic stage, which was lower than the potential fecundity (17188 ± 6917 eggs). Histological examination of the gonads revealed the existence of atretic oocytes in early vitellogenic stages (October and November). This investigation highlights the temporal variation in the initiation and duration of the reproductive activity of the European perch in this region compared to other geographical regions. The results emphasize the necessity of specific temporal management in fishing of European perch based on spatial differences in reproductive biology.     

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.     

Identification of a female spawn‐associated Kazal‐type inhibitor from the tropical abalone Haliotis asinina

Abalone (Haliotis) undergoes a period of reproductive maturation, followed by the synchronous release of gametes, called broadcast spawning. Field and laboratory studies have shown that the tropical species Haliotis asinina undergoes a two‐week spawning cycle, thus providing an excellent opportunity to investigate the presence of endogenous spawning‐associated peptides. In female H. asinina, we have isolated a peptide (5145 Da) whose relative abundance in hemolymph increases substantially just prior to spawning and is still detected using reverse‐phase high‐performance liquid chromatography chromatograms up to 1‐day post‐spawn. We have isolated this peptide from female hemolymph as well as samples prepared from the gravid female gonad, and demonstrated through comparative sequence analysis that it contains features characteristic of Kazal‐type proteinase inhibitors (KPIs). Has‐KPI is expressed specifically within the gonad of adult females. A recombinant Has‐KPI was generated using a yeast expression system. The recombinant Has‐KPI does not induce premature spawning of female H. asinina when administered intramuscularly. However it displays homomeric aggregations and interaction with at least one mollusc‐type neuropeptide (LRDFVamide), suggesting a role for it in regulating neuropeptide endocrine communication. This research provides new understanding of a peptide that can regulate reproductive processes in female abalone, which has the potential to lead to the development of greater control over abalone spawning. The findings also highlight the need to further explore abalone reproduction to clearly define a role for novel spawning‐associated peptide in sexual maturation and spawning. Copyright © 2016 European Peptide Society and John Wiley & Sons, Ltd.     

Spawning in a cold bath: reproduction of polar and deep‐sea fish family Psychrolutidae

This study describes the spawning of the fatheads Psychrolutes marmoratus and Cottunculus granulosus, two psychrolutid species that inhabit the shelf edge and continental slope of the south‐west Atlantic. Females lay large eggs of c. 2·5 mm (P. marmoratus) and 4·5–5·0 mm (C. granulosus); fecundity is from the hundreds (C. granulosus) to a few thousand eggs (P. marmoratus). Egg maturation is synchronous in P. marmoratus with an autumn–winter peak of spawning and group‐synchronous in C. granulosus, which reproduces all year round. In the fishery, females predominate among adult fish in both species, possibly indicating male nest guarding on hard grounds inaccessible to fishing vessels. The reproductive strategy of representatives of the Psychrolutidae is similar to that of other sculpins of the superfamily Cottoidea.     

Sexual Maturation, Annual Reproductive Cycle, and Spawning Periodicity of the Shore Scorpionfish, Scorpaenodes littoralis

The ovarian structure, sexual maturation, annual reproductive cycle, and spawning periodicity of the shore scorpionfish, Scorpaenodes littoralis, in Uchiura Bay, central Japan, were examined using specimens collected between May 1995 and March 1998 and fishes reared in laboratory. The ovarian stroma and blood vessels run longitudinally through the center of each ovarian lobe. The ovarian peduncles radiate from the central stroma. During the spawning season, gelatinous material is secreted from the epithelia of both the ovarian peduncle and ovarian wall, and the epithelia show morphological changes accompanying the ovarian maturation cycle. The minimum standard length at maturity was 55.2mm for males and 40.2mm for females. Males with mature testes were collected from March to November. Females in the mature or post spawning stages were collected between May and October, when the mean gonadosomatic indices were also high. This indicates that the spawning season of this species occurs between May and October. Four successive types of oocytes were grouped in the mature ovary, comprised of mature, late and early vitellogenic and previtellogenic oocytes respectively, suggesting that this species is a multiple spawner. Four captive females spawned repeatedly at intervals of 2–8 days over a prolonged period (4–8 months); a 2-day spawning interval was the most common for all females. This suggests that female S. littoralis have a 48-h spawning cycle in captivity.     

Population structure and reproductive biology of Schilbe intermedius (Teleostei: Schilbeidae) in the Pendjari River,Benin

This study, the first on fish reproduction in the Pendjari River, investigated aspects of the reproductive biology of Schilbe intermedius. A total of 429 females and 239 males were collected from March 2007 to February 2008. Females were larger than males and the sex ratio was 1:1.8 in favour of females. Size at first maturity was estimated to be 14.9 cm and 16.1 cm for males and females, respectively. Absolute fecundity ranged from 1 006 to 83 980 (22 421 ± 16 083) oocytes, and mean relative fecundity was 201 ± 162 oocytes g^?1 of total body mass. Frequency distributions of oocyte diameter suggested synchronous development, with total spawning. Spawning lasted from June to November, coinciding with peaks in rainfall and flooding. Larger females began spawning about two months before smaller ones.     

Reproductive Timing of Fishes in a Tropical Intermittent Stream

Six fish species were studied in an intermittent lowland stream in Trinidad, West Indies for 28 months from 1980 to 1982. They were Gasteropelecus sternicla, Corynopoma riisei, Astyanax bimaculatus, Hemigrammus unilineatus, Corydoras aeneus and Poecilia reticulata. Peaks in GSIs and presence of mature adults and juveniles, as determined from monthly field collections, indicated reproduction coincident with the rainy seasons in all species except Poecilia. Gasteropelecus bred for a short period at the beginning of the main rainy season while Corynopoma, Corydoras and Hemigrammus had extended periods of breeding activity each year coincident with high rainfall. The presence of juveniles suggests that Astyanax also bred during the rainy season. Poecilia reproduced continuously throughout the study period but exhibited discharge-related adult stock fluctuations that may have influenced reproductive activity. Maximum ovarian fecundity correlated with species size suggested body size limitation on fecundity for small species such as Corynopoma and Hemigrammus. Size frequency distributions of oocytes in mature ovaries indicate synchronised ovum maturation in Astyanax and possibly Gasteropelecus, while Hemigrammus, Corynopoma and Corydoras showed evidence of continuous maturation of oocytes and multiple spawning. Prolonged small brood spawning was confirmed in the laboratory for Corynopoma and Hemigrammus and resulted in spawning fecundities up to 11 times greater than ovarian fecundities for Corynopoma. It is concluded that the conditions of intermittency in this stream did not significantly alter the reproductive styles of these species as described for other Neotropical environments, perhaps because of their opportunistic nature. Patterns of spawning for the characoids can be directly related to size and phylogeny.     

Reproductive guilds (maturation,spawning frequency and fecundity) in the black pomfret,Parastromateus niger (Carangidae) in the Kuwaiti waters of the Arabian Gulf

Oogenesis, oocyte maturation pattern, spawning rhythm, spawning frequency, batch fecundity and oocyte diameter–frequency distribution of the black pomfret, Parastromateus niger (Bloch, 1795) in Kuwaiti waters were investigated from October 2003 to September 2005, using histological and morphological methods. The process of development is divided into four major phases: (i) primary growth phase; (ii) secondary growth phase; (iii) maturation phase; and (iv) spawning phase, followed by the regressed phase. Development of the yolky oocyte is an asynchronous process resulting, by the time of oocyte maturation, in a clear differentiation between a ready batch of oocytes (ready for spawning) and a reserve pool. Consequently, P. niger is capable of spawning multiple times throughout the reproductive season. Spawning frequency estimates, based on final oocyte maturation (FOM) method indicated that the species spawns once every 2.8 days during an 8‐month spawning season lasting from February to September, with a potential annual number of 22.4 spawns. Batch fecundity (BF) (2132–2001 648, mean 406 010 eggs), was significantly positively related to both standard length (SL) (P < 0.05) and ovary‐free body weight (OFBW) (P < 0.05), both parameters being good predictors of BF (r² = 30.8% for SL, from 22 cm onwards, and r² = 29.6% for OFBW, from 129.5 g onwards). No significant differences in monthly BF were found throughout the spawning season. Relative batch fecundity was 336 eggs/g OFBW; thus, estimate for potential annual relative batch fecundity was 7526 eggs g^?1 OFBW. The oocyte diameter–frequency distribution analysis revealed a multimodal distribution (at 100–200, 300–400 and 500–700 μm), confirming the evidence of multiple spawning.     

Reproductive characteristics and gamete development of the soft coral Sclerophytum cf. heterospiculatum in Okinawa Island,Japan

Sexual reproduction data are important to understand how organisms can replenish their populations and proliferate on coral reefs. Despite the importance of such data, the reproductive characteristics of most soft coral species are still unknown. Here, we examined the reproductive strategies of a species from the often-dominant genus Sclerophytum in a coral reef on subtropical Okinawa Island, Japan. DNA barcoding and histological examinations of the tissues were conducted to confirm colony conspecificity and identify reproductive characteristics, respectively, between March 2020 and March 2021. Results indicated that the studied species, identified as Sclerophytum cf. heterospiculatum, exhibits gonochorism with longer oogenesis and shorter spermatogenesis. Female colonies produced immature oocytes throughout the year, with mature oocytes observed from late July to early September, and thus, extended spawning is likely characteristic of this species. In male colonies, spermatogenesis took place over ~5 months, with spermaries present from April through August. Mature spermaries were noted beginning in July and the inferred peak of sperm release was between late August and early September, which suggests that spermatogenesis duration was ~5 months. The largest mean oocyte and spermary sizes (628.45 ± 61.36 and 240.04 ± 49.49 μm, respectively) were both recorded in August. Gamete spawning presumably occurred during the summer season, which suggests seasonality in reproduction as influenced by changes in seawater temperature. However, the proximate cue for exact dates of spawning could be the lunar period because the inferred release of spawning materials seemed to occur between full moon and last-quarter moon phases in both the months of August and September. The results of this study represent the first detailed report of reproductive characteristics of the genus Sclerophytum in Japan.