Batch Fecundity Research Articles

Reproductive Potential of the Mackerel Scad, Decapterus macarellus (Cuvier, 1833) in the Coastal Waters of Tanzania

This study investigated the reproductive biology of Decapterus macarellus locally known as ''Msumari", one of the most economically important scad fish along the coastline of Tanzania. Fish samples were collected from ring net artisanal fishers operating in Tanga and Bagamoyo coastal waters, monthly between April 2019 and September 2020. Findings indicated that D. macarellus spawns throughout the year with peaks in August at Tanga and September at Bagamoyo. Overall sex ratios (M: F) were 1:1.03 (Tanga) and 1:1.2 (Bagamoyo) in favour of females. The males and females of D. macarellus at Tanga attained the first maturity at 145.5 mm and 153.2 mm, respectively, whereas at Bagamoyo males attained first maturity at 149.9 mm and females at 156.9 mm. Batch fecundity was not statistically significant (U = 500.5; p = 0.73), with Tanga having mean values (± SE) of 46,105.9 ± 4243.4 ova and Bagamoyo 43,082 ± 2272.9 ova. Although this species appears to spawn all year round, management interventions such as seasonal closure and reduced fishing effort should be used during their spawning peaks to protect the spawners, recruits and ensure the species' long-term survival in the Tanzanian coastal waters.
 Keywords: Scad; Decapterus macarellus; reproductive potential; ring net fishery; Tanzania.

Diurnal maturation rhythm, spawning frequency and fecundity of Diaphus fulgens (Teleostei: Myctophidae) in the Kuroshio waters of the East China Sea

Diaphus fulgens is a diel vertical migrating myctophid, and it is the dominant Diaphus species in the Kuroshio waters of the East China Sea. The diurnal maturation rhythm, spawning frequency, and fecundity of this species were examined based on individuals (24.3–43.1 mm standard length) collected in different periods of the day during the primary spawning season of late winter. Based on ovarian histological analysis, the nucleus migration occurred during the nighttime to the following early morning, and hydration occurred during the daytime in the mesopelagic layer. The appearance of late stage hydrated oocytes and early stage post-ovulatory follicles showed that D. fulgens actively spawned shortly after sunset during 2000–2100 h. This species is concluded to migrate vertically with the eggs to the epipelagic layer during twilight, although the possibility of spawning in the mesopelagic layer before reaching the epipelagic layer can not be ruled out. Darkening after sunset would potentially work as the triggering mechanism for spawning behavior. Based on the diurnal maturation rhythm, estimation methods of the spawning frequency and batch fecundity were confirmed for myctophids. Diaphus fulgens is a multiple batch spawner with a short interspawn period of 2.2–4.0 days. Mean batch fecundity (± standard deviation) was 399 ± 102 eggs, and the lifetime egg production per female was estimated to be 3000–5400 eggs. The high potential of egg production would contribute to the recruitment of sufficient numbers to maintain populations.

Reproductive dynamics of Pacific bluefin tuna (Thunnus orientalis) off the Nansei Islands, southern Japan

To describe seasonal changes in the reproductive traits of Pacific bluefin tuna (Thunnus orientalis), we examined the spawning season, spawning fraction (SF), spawning interval, batch fecundity (BF) and monthly changes in the horizontal distribution of spawning fish (SP) in the Nansei Islands and the waters off southwestern Honshu Island, Japan. SP were observed at sea surface temperatures (SSTs) between 19 and 29 °C, and the frequency of SP tended to increase with SST. SP were observed from early May to mid-July and most frequently in late June. The SP distribution in the Nansei Islands tended to expand northward with time. Mature female fish were widely distributed between the Nansei Islands and the waters off southwestern Honshu Island throughout the study period. The total SF during the spawning season was 0.24, which was equal to the 4.17-day spawning interval. The SF tended to increase with time. The number of days since the start of the fishing season (Days) positively affected the probability of the occurrence of specimens with postovulatory follicles among mature fish. The mean and relative BFs during the spawning season were 9.74 ± 6.72 (million oocytes) and 64.8 ± 38.4 (oocytes/g), respectively. The BF was positively affected by increases in the fork length (FL) and Days. These results suggest that the reproductive traits of Pacific bluefin tuna in the Nansei Islands are influenced by environmental and maternal conditions.

Spatiotemporal variability in the reproductive biology of yellowfin tuna (Thunnus albacares) in the eastern Pacific Ocean

The reproductive biology of yellowfin tuna (Thunnus albacares) was investigated through at-sea sampling of ovaries from 1728 females, across 12 length classes from 40 to 160 cm fork length, from four spatial strata (northern (N), central coastal (CC), central offshore (CO), and southern (S)) of the eastern Pacific Ocean, caught by purse-seine vessels from January 2009 to November 2016. Histological evaluations of the ovarian tissues provided the foundation for the estimates of length-specific reproductive characteristics. Spawning was widespread from about 25°N to 16°S between 78°W and 148°W, occurring throughout the year from 5°N to 15°N. North of 20°N, spawning took place during April–December, and south of 5°S, spawning took place during January–June. Spawning was observed for fish captured in dolphin, floating-object, and unassociated sets. Although spawning occurred at sea-surface temperatures from 25 °C to 32 °C, 73.0% of the spawning took place between 27.0 °C and 29.0 °C. Results of fitting a general additive model (GAM) to the maturity-at-length data indicated significant spatial variation in maturity, with estimated lengths at 50% mature of 90.6 cm in the S area, 83.2 cm in the N area, 78.6 cm in the CC area, 70.9 cm in the CO area, and 81.6 cm for the combined data. Results of fitting GAMs to maturity-at-length data sets from the current study and from a previous study executed during 1987–1989, indicated significant temporal variation for the CO, CC, and S areas, and the combined data sets. The estimated lengths at 50% mature for the combined data, for the same spatial strata, from the earlier samples and from those in the current study were 90.4 cm and 78.6 cm, respectively. The observed batch fecundities from 146 fish, based on counts of late-stage migratory-nucleus or hydrated stages of oocytes, ranged from about 54 thousand oocytes for an 87 cm female to about 7.2 million oocytes for a 153 cm female. The average size of the 146 females was 118 cm, and the average batch fecundity was about 2.3 million oocytes. The estimated mean relative fecundity for 136 females, which were weighed, was 60.95 oocytes per gram of body weight. The fraction of all mature females with postovulatory follicles was 0.56, equivalent to a mean spawning interval of 1.79 d, whereas for reproductively active females the fraction spawning per day was 0.81, equivalent to a mean spawning interval of 1.23 d.

Reproduction ecology of an emerging fishery resource, the amphibious mudskipper Periophthalmus chrysospilos, in the Mekong Delta.

Populations of Periophthalmus chrysospilos, the Gold‐spotted mudskipper, within the Mekong Delta are facing extirpation risks due to indiscriminate harvesting for the growing aquarium and food‐fish trade. This study provides some of the first information on reproductive ecology—such as spawning type and season, length at first maturity, and batch fecundity—of this species, to be used in their management. The sex ratio of wild populations, based on 1031 individuals (523 males and 508 females) is 1:1. The gonadosomatic index (GSI) values are exhibit a non‐normal distribution and changed with gender, season, and site. A combination of GSIs and the monthly appearance of mature gonads suggest that this species reproduces throughout the year, with peak from July to October. This species exhibits sexual and spatial variation in size at first maturity (Lm ) as Lm is 6.2–8.6 cm in males and 6.4–7.3 cm in females. The batch fecundity (F = 2614 to 23,465 eggs/female) exhibits non‐normal distribution and varies with site, with the highest values at Dam Doi, Ca Mau (13,336 ± 1,279 SE) and the lowest at Tran De, Soc Trang (6654 ± 851 SE). In addition, batch fecundity is directly proportional to body size due to high determination relationships between batch fecundity and fish size (r 2 > 0.64 for all cases). Information derived on the reproductive biology of this species can inform its conservation, sustainable exploitation, and ex situ propagation.

Reproduction of the Blue Jack Mackerel, Trachurus picturatus, in Western Portugal: Microscopic Gonad Analysis Reveals Indeterminate Fecundity and Skipped Spawning Patterns.

Blue jack mackerel, Trachurus picturatus, is the fifth most landed fish species in mainland Portugal, but information on its reproductive biology is scarce. From September 2018 to August 2019, 626 specimens were collected from commercial vessels to clarify the reproductive strategy of the T. picturatus population off the west coast of Portugal. The proportion and length range of males and females were similar. Only three of the specimens collected were categorized as immature, indicating that the fish caught in the fishery are primarily mature. The spawning season lasted from late January until the end of March, with gonadosomatic indices being similar for males and females. Fecundity was indeterminate, and estimated batch fecundity ranged between 6,798 (at 25.4 cm TL) and 302,358 oocytes (at 33.8 cm TL). The low number of females showing direct evidence of imminent or recent spawning suggests a low number of spawning events. In addition, 12.7% of females were considered non-reproductive due to ovary abnormalities including parasitic infection by Kudoa species, atretic structures and skipped spawning events. This study highlights the importance of accounting for skipped spawning events and ovary abnormalities in the management of species fisheries.

Reproductive dynamics of the invasive lionfish (Pterois miles) in the Eastern Mediterranean Sea.

The lionfish Pterois miles invaded the Mediterranean Sea in 2012 and spread fast to the entire eastern basin. This study provides evidence of successful spawning and the first detailed analysis of P. miles ovarian dynamics in the Mediterranean Sea. The ovarian reproductive phases of mature females collected from Cyprus (eastern Mediterranean) between September 2017 and August 2018 were analysed, both macroscopically and histologically. The results suggested a prolonged oocyte recruitment and development season, and a spawning season that primarily occurred during summertime, even though spawning-capable females were caught also in autumn. A year-round spawning activity may have been inhibited due to seasonal variations in water temperature. Multiple oocyte developmental stages co-occurred in females at different reproductive phases, indicating that more than one oocyte batches were released per spawning season. The analysis of the spawning batch formation enabled the batch fecundity estimation at 3225-63149 oocytes. The oocyte development pattern described in this study shared characteristics with the indeterminate fecundity type, where new oocytes are recruited to the secondary growth phase in parallel with spawning activity. Climate change is likely to extend the spawning season of lionfish in the Mediterranean Sea and further favour its invasion. The information provided in this study is vital for the design of strategic and effective management plans to restrain the expansion of this highly invasive fish.

Experimental evidence for population variability of reproductive traits in Japanese anchovy Engraulis japonicus

Small pelagic fishes show spatiotemporal variations in reproductive traits due probably to responses to varying environmental conditions, but potential genetic contributions to such variations have received little attention. This study compared several reproductive traits of Japanese anchovy between two geographically isolated populations, from the central Seto Inland Sea and Omura Bay, western Japan, under common environmental conditions over three generations. There were no significant differences in age and standard length at sexual maturation between populations. Temperature-mediated variation in egg size was found in the two populations with decrease in egg size as temperature increased. However, regression analysis showed that the relationship between egg size and temperature differed significantly between the two populations over three generations. There was also a significant difference in the relative batch fecundity of the F1 and F2 generations between populations. Hence, females from the central Seto Inland Sea could produce a larger number of smaller eggs than females from Omura Bay. Variation in egg size appears to reflect significant differences in larval size at hatch and the onset of feeding in waters of different temperatures. These findings suggest that the thermal reaction norms of egg size observed in the two populations could have genetic contributions and that their egg traits may mediate a possible difference in offspring viability during early life stages.

Mackerel (Scomber australasicus) Reproduction in Northeastern Taiwan

Blue mackerel (Scomber australasicus) is a crucial target species for coastal fisheries in Taiwan, and additionally it has maintained its status as the highest-produced species. The timely measurement of spawning status is crucial for determining the correct management strategy for this species. The objective of this study was to determine size at maturity, fecundity, batch fecundity, and spawning frequency on the basis of samples collected from Nan-Fang-Ao fishing port in Yilan, during the spawning season from 2017 to 2019. Histological sections indicated that the blue mackerel were multiple spawners; a higher percentage of female fish spawned at the peak of the gonadosomatic index. The 50% sizes at maturity were 32.02, 32.13, and 29.64 cm. Mean total fecundity (batch fecundity) was 165 (103), 229 (96), and 210 (68) oocytes per ovary-free weight (g) for 2017, 2018, and 2019, respectively; fecundity was determined through observation of postovulatory follicles (POFs). The spawning frequencies (spawning fraction) in 2017, 2018, and 2019 were 3–10 days (0.13), 4–14 days (0.08), and 4–12 days (0.09), respectively. The spawning frequencies determined through the three estimated methods, namely the sums of (a) hydrated and Day 0 POFs; (b) Day 1+ POFs, and (c) all data combined, were 1 spawning event per 8, 10, and 9 days, respectively. The reproduction of the blue mackerel was greater in 2017 than it was in 2018 or 2019, as indicated by the higher batch fecundity and shorter spawning seasons. Environmental factors should also be considered as a major factor influencing successful reproduction and spawning season

Reproduction and fecundity of invader of internal insemination Trachelyopterus galeatus in a Neotropical floodplain

After the formation of Itaipu Reservoir, the invader Trachelyopterus galeatus colonized the upper Paraná River. Light microscopy was used to describe gametogenesis and the reproductive phases of females and males. The following data were verified: diameter of the oocytes, spawning type, batch fecundity by ovary weight, standard length, and total weight of the fish, along with the regions where this species reproduced in the upper Paraná River floodplain. A total of 470 specimens were collected quarterly in 2016, 2018 and 2019, and bimonthly in 2017. The gonads were fixed in a Karnovsky solution, dehydrated, infiltrated, and embedded in historesin. The histological slides were stained using PAS + iron hematoxylin + metanil yellow, analyzed and photographed under an image-capturing microscope. As regards diameter of the oocytes and fecundity estimates, ovaries whose oocytes were measured under a stereomicroscope were sampled. In the oogenesis, undifferentiated and differentiated oogonia, early primary growth oocytes, secondary growth oocytes, full-grown oocytes and maturing oocytes were recorded. In the spermatogenesis, primary and secondary spermatogonia, primary and secondary spermatocytes, spermatids and spermatozoa were recorded. The reproductive phases found for females and males were: immature, early development, late development, spawning/sperm-releasing capable, regression, and regeneration. Trachelyopterus galeatus prefers to occupy and reproduce in the Ventura, Patos, Guaraná, Fechada, Garças, and Pau Véio lagoons. The diameter of the oocytes varied from 0.4 to 2.9 mm. Females spawn, on average, 113 oocytes per batch. Batch fecundity variation shows that the larger the ovary, standard length, and total weight, the larger the number of oocytes to be spawned. This invader possesses reproductive success in the upper Paraná River floodplain, especially in lagoons.

Ovarian and spawning reference, size at first maturity and fecundity of Glossogobius giuris caught along Vietnamese Mekong Delta

This study investigates the ovarian development, spawning patterns, maturity size and fecundity of the goby Glossogobius giuris–a commercial fish in the Vietnamese Mekong Delta–based on the data analysis of 659 individuals. Specimens were caught using trawl nets from four sites representing freshwater (Cai Rang, Can Tho) to salinized regions in the dry season (Long Phu, Soc Trang), and brackish water regions (Hoa Binh, Bac Lieu and Dam Doi, Ca Mau) over the 12 months of 2020. Histological analysis showed that it was a multi-spawner as different stages of oocytes appeared in mature ovaries. The fish could spawn throughout the year, with a peak in April at the freshwater region and in September at salinized and brackish areas as mature ovaries appeared monthly during the studied period and gonadosomatic index displayed the highest value in April and in September, respectively. This goby’s primary egg releasing time tended to be regulated by salinity changes over the four sampling sites. Likewise, size at first maturity of this species could be related to the salinity variation as this value was the longest in freshwater (6.14 ± 0.17) and the shortest in the salinization region (4.82 ± 0.66). Batch fecundity is measured at 5,118–100,003 eggs/female and related to fish length and weight (r2 > 0.76). Findings can be useful for the development of fish conservation strategies and artificial reproducing studies.

Evidencing some reproductive aspects of a commercial gobiid species Glossogobius aureus Akihito & Meguro, 1975 in Hau River, Vietnam

This study supplies knowledge on the reproductive traits of Glossogobius aureus, one of the commercial fishes living in brackish water and freshwater. A collection of 742 G. aureus specimens was caught using gill nets from January to December 2020. The results of the gonadal breeding frequency and gonadosomatic indices showed that G. aureus spawned year-round, but with higher activity during four months, from August to October, of the wet season. Size at first maturity (Lm) of males was higher than that of females in all study sites. The batch fecundity (F) was 1044–27,349 eggs/female and increased with fish size, as shown by the high determination values (r2 > 0.6). The study results provide new references on the reproductive biology of the population of Glossogobius aureus which will help in the sustainable management of its fisheries in the studied areas.

How does spawning frequency scale with body size in marine fishes?

AbstractHow does fecundity scale with female size? Female size not only affects the number and size of offspring released in any one reproductive bout (i.e. batch fecundity) but also affects frequency of bouts that occur within a given spawning season (i.e. spawning frequency). Previous studies have noted contrasting effects of female size on spawning frequency such that the effect of female size on reproductive output and total egg production of a population remains unclear. If smaller females spawn more frequently, this could effectively nullify hyperallometry—the disproportionate contribution of larger females to batch fecundity. Here, we explore the relationship between female size and spawning frequency in marine fishes and test this relationship while controlling for phylogeny. Within all of the species considered, spawning frequency scaled positively with body size. Comparing across species, the smallest species showed steeper scaling than the largest. Considering only batch fecundity scaling probably underestimates the relationship between body size and absolute fecundity for many species; reproduction is likely to be more hyperallometric than is currently appreciated based on batch fecundity estimates. Second, an understanding of fecundity scaling depends on estimates of batch fecundity, spawning frequency and spawning duration—we have far more estimates of the first parameter than we do the others, and more studies are required.

Ovarian dynamics, batch fecundity and spawning phenology of the lessepsian migrant Etrumeus golanii DiBattista, Randall & Bowen, 2012 (Clupeidae: Dussumieriinae)

The Golani’s round herring Etrumeus golanii is an Erythraean small pelagic fish (lessepsian migrant) that entered into the Mediterranean Sea through the Suez Canal. It has expanded its distribution from the east to the western Mediterranean with well-established local populations. We investigated basic aspects of its reproductive biology off the island of Crete (eastern Mediterranean) using ovarian histology and analysis of oocyte size-frequency distributions. The species exhibited a protracted breeding period (winter to early summer), with all ovaries examined during the main spawning season having markers of recent (postovulatory follicles, POFs) or imminent spawning (advanced oocyte batch in germinal vesicle migration or hydration). The advanced batch (AB) increased rapidly in size and was fully separated from the remainder, less developed oocytes in 95% of females with “old” POFs (POFs with signs of degeneration) and all females in final maturation. The growth of the subsequent batch (SB) was arrested at sizes <630 µm until full maturation of the AB. Mean diameter of hydrated oocytes ranged from 1181 to 1325 µm and relative batch fecundity was low ranging from 56 to 157 eggs g-1. The simulation of a coupled hydrodynamic/biogeochemical model (POM/ERSEM) provided evidence that E. golanii takes advantage of the seasonal cycle of planktonic production to reproduce and exhibits monthly changes in batch fecundity that appear to be closely related with the seasonal cycle of mesozooplankton concentration.

REPRODUCTION ASPECTS OF COBIA CAUGHT IN PERNAMBUCO COAST, NORTHEASTERN BRAZIL

Aspects of the reproduction of cobia (Rachycentron canadum) population from the coast of Pernambuco State, Northeastern Brazil, were studied from February 2004 to August 2006. One hundred eleven individuals were analyzed: 54 females with fork length (FL) ranging from 40 to 137 cm (mean ± standard deviation: 90.7 ± 18.1 cm) and 57 males with FL from 43 to 114.5 cm (82.4 ± 17.0 cm). Histological analysis was used to identify maturational phases. Spawning capable females were found from August to May, except in December, while mature males were present throughout the year, except in July. Size at first maturity (L50) obtained by Bayesian analysis was 72.51 cm FL for females and 60.69 cm FL for males. Overall batch fecundity ranged from 192,063 to 1,600,513 oocytes (722,398 ± 430,911) and mean relative batch fecundity ranged from 32.9 to 104.8 (71.1 ± 29.8) oocytes per gram of female body weight. The data indicate that the reproduction of cobia off the coast of Pernambuco occurs throughout the year, but with peaks between February and April, period in which gonadosomatic indices reach the maximum values and then decrease until May for females and males.

Bioenergetics of egg production in Northeast Atlantic mackerel changes the perception of fecundity type and annual trends in spawning stock biomass

Egg surveys are used worldwide for the estimation of spawning stock biomass (SSB) of small pelagic fish species, requiring detailed knowledge about their reproductive biology. In the present study, we revisit the current conceptual framework of teleost fecundity types using Northeast Atlantic (NEA) mackerel (Scomber scombrus) as case study due to conflicting views across different assessment methods. We hypothesized that the herein presented unique time series on protein and lipid content for this stock would help in resolving the long-lasting, intrinsic fecundity type problem. First, we document that the body surplus energy has varied substantially over time, with a significant drop to historically low levels following a stock increase from 2005 to 2015. This fluctuating pattern is in stark contrast to the stable relative fecundity (oocyte g−1 females) measured in connection with the egg surveys. Second, we show that the feeding levels are at the highest during the spawning season. These findings are consistent with an indeterminate fecundity type as opposed to the presently accepted determinate-type classification dating back to the 1990s. Furthermore, we quantify the batch fecundity and find it to be largely constant. Hence, the main reproductive output regulator that is driven by the bioenergetic status should therefore be the number of batches shed. Based on this novel framework for an indeterminate spawner, we provide alternative estimates of relative realized fecundity, which significantly change the egg survey-based SSB indices, reduces the contrast to the other data sources in the mackerel stock assessment (1990–2019), improves the assessment model fit and reduces the uncertainty of the stock size estimate. The presented algorithms and lines of thinking are applicable to other teleosts and may improve the precision and accuracy of the estimation in cases where the annual egg production method is used to assess stock size.

Reproductive strategy of spiny gurnard Lepidotrigla dieuzeidei Blanc and Hureau, 1973 from the south-eastern Adriatic Sea

This study provides the first data on the reproductive biology of the spiny gurnard Lepidotrigla dieuzeidei. A total of 1027 individuals were collected monthly from September 2011 to August 2012. The total length of the individuals in the sample ranged from 7.46 cm to 14.62 cm with a female to male ratio of 1 to 0.59. Positive allometric growth was observed for both females (b=3.07) and males (b=3.08). Variations of condition factor were similar in both sexes with mean values of 1.07 for females and 1.01 for males. The fish L. dieuzeidei had a long spawning period extending from November to July based on monthly values of gonadosomatic index. Histological analysis showed that this fish was multiple synchronous developments of ovaries with multiple spawning events. The ovaries were always represented with a group of primary oocytes and a diverse population of vitel-logenic oocytes, each specially recruited during the final stages of maturation in uniform or uneven phases. Batch fecundity was estimated gravimetrically using the hydrated oocyte method and was estimated to be around 558 to 10.230 oocytes per female. L. dieuzeidei is an important by-catch species and data from this study represent a valuable contribution to stock management.

Temperature drives spatial and temporal variation in the reproductive biology of the blue swimmer crab Portunus armatus A. Milne-Edwards, 1861 (Decapoda: Brachyura: Portunidae)

Abstract Sound fisheries management requires knowledge of how the reproductive biology of targeted species varies over space and time and responds to external drivers. We determined the size at maturity and fecundity of the blue swimmer crab Portunus armatus (A. Milne-Edwards, 1861) (Brachyura: Portunidae) along the west coast of Australia at monthly, annual and interdecadal (1990s versus 2010s) time scales. The size at maturity of females determined by abdominal morphology (carapace width (CW) at 50% maturity (CW50)) was highest in sub-tropical Shark Bay at 26°S (104 mm), and declined latitudinally to temperate Geographe Bay at 34°S (93 mm). A notable exception was in a marine embayment at 32°S (Cockburn Sound), where CW50 was significantly lower than all other locations (83 mm). In contrast, batch fecundity was lower in sub-tropical (830,000 eggs at 127 mm CW) than temperate waters (950,000–990,000 eggs). Temporally, CW50 was significantly higher during January-June (typical growth period, encompassing the warmest months of the year) than during July-December (breeding period), and also differed between months, years, and decades. Positive correlations between water temperature, monthly and annual estimates of CW50, and functional maturity (size at first ovigery), were detected in most locations. Annual CW50 also increased with population density, particularly in locations where abundances and biomass were lowest. Results highlight plasticity in the reproductive biology of this portunid in response to environmental drivers such as temperature. Regular review of such parameters is important for ensuring robust fisheries management and stock assessments.

A Quick Method for Estimating Batch Fecundity in Bigheaded Carp

AbstractFecundity is a necessary metric to assess reproductive potential (e.g., spawning potential ratio and recruitment overfishing) in invasive fishes, yet the direct measurement of fecundity is often difficult, impractical, and time consuming. Therefore, the ability to estimate fecundity from field measurements (i.e., TL, relative weight [Wr], or ovary weight) can be a valuable tool for fisheries managers to estimate reproductive potential. The goal of this study was to relate the batch fecundity of invasive Silver Carp Hypophthalmichthys molitrix and Bighead Carp H. nobilis to metrics that can be quickly measured to eliminate the need for direct enumeration. Silver and Bighead carp were collected from the upper Mississippi River (UMR) in the summer of 2016 and 2017. Subsamples of mature (spawning capable) ovaries were preserved, enumerated, and then related to ovary weight, TL, weight, and Wr. An equation for estimating Silver Carp batch fecundity from ovary weight in the UMR, corrected for ovary membrane weight, was developed: {ovary weight – [0.222 × (ovary weight0.7589)]} × 794 (SE = 11). Batch fecundity for Silver Carp from Pools 17–20 of the UMR averaged 1,230,930 ± 68,983 eggs (mean ± SE). Ovary weight was the strongest predictor of fecundity, but TL, weight, and Wr also showed significant relationships with fecundity for Silver Carp. Batch fecundity for Bighead Carp averaged 1,043,953 ± 82,360 eggs, but the number of eggs per gram showed significant spatial variation; therefore, no fecundity equation was developed for this species. Future work should evaluate the frequency of Silver Carp spawns within a season and how batch fecundity varies among multiple spawning events. Fecundity estimates can be used to determine spawning potential ratios, which can help in evaluating management strategies.

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 (IG ) revealed 1% to be a clear cut-off indicating maturity. Females are considered capable of spawning from April to June when IG 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% IG 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.