Batch Fecundity Research Articles

Spawning Dynamics and Size Related Trends in Reproductive Parameters of Southern Bluefin Tuna, Thunnus maccoyii.

Knowledge of spawning behaviour and fecundity of fish is important for estimating the reproductive potential of a stock and for constructing appropriate statistical models for assessing sustainable catch levels. Estimates of length-based reproductive parameters are particularly important for determining potential annual fecundity as a function of fish size, but they are often difficult to estimate reliably. Here we provide new information on the reproductive dynamics of southern bluefin tuna (SBT) Thunnus maccoyii through the analysis of fish size and ovary histology collected on the spawning ground in 1993–1995 and 1999–2002. These are used to refine previous parameter estimates of spawning dynamics and investigate size related trends in these parameters. Our results suggest that the small SBT tend to arrive on the spawning ground slightly later and depart earlier in the spawning season relative to large fish. All females were mature and the majority were classed as spawning capable (actively spawning or non-spawning) with a very small proportion classed as regressing. The fraction of females spawning per day decreased with fish size, but once females start a spawning episode, they spawned daily irrespective of size. Mean batch fecundity was estimated directly at 6.5 million oocytes. Analysis of ovary histology and ovary weight data indicated that relative batch fecundity, and the duration of spawning and non-spawning episodes, increased with fish size. These reproductive parameter estimates could be used with estimates of residency time on the spawning ground as a function of fish size (if known) and demographic data for the spawning population to provide a time series of relative annual fecundity for SBT.

Gonad development and reproduction of the ballyhoo half beak, Hemiramphus brasiliensis from the coastal waters of Rio Grande do Norte, Brazil.

The gonad development and reproductive aspects of Hemiramphus brasiliensis from the coastal waters of Rio Grande do Norte, Brazil were verified. This paper presents data on the length-weight relationship, sex ratio, length at first sexual maturity, gonad development, reproductive period and fecundity of H. brasiliensis. Females of this species predominated in the sampled population and were larger in size than the males. The length at the first sexual maturation of males was 20.8 cm and that of females was 21.5 cm. The macroscopic characteristics of the gonads indicated four maturation stages. Histological studies of gonads of H. brasiliensis showed six phases of oocyte development and four phases of spermatocyte development. The batch fecundity of this species is 1153 (± 258.22) oocytes for 50 g body weight of female. The microscopic characteristics of gonad development indicate that H. brasiliensis is a multiple spawner, with active reproductive period during the months of January to June and October. The reproductive period of this species is independent of the rainy period of the region.

Assessing reproductive resilience: an example with South Atlantic red snapper Lutjanus campechanus

We developed a conceptual model of reproductive resilience based on spatio-tempo- ral diversity in spawning activity and the 'big old fat fecund female fish' effect, i.e., trends in reproductive traits with size and age. We chose red snapper Lutjanus campechanus as our case study, as this species is highly fecund, currently overfished, and long-lived (50+ yr). The intrinsic reproductive resilience of red snapper was assessed in terms of spawning site distribution, vari- ability in time of spawning, and potential reproductive lifespan. To assess how age truncation might erode reproductive resilience, we evaluated the strength of the relationship between size and age and the following traits: spawning habitat, reproductive timing, batch fecundity, and egg quality. Few fish were older than 7 yr. Although younger fish occurred in a more restricted range of depths, there was no trend between size or age and depth. Spawning activity was well distrib- uted over space and time, with actively spawning females collected at 92 of 195 sampling sites over an extended spawning season. Larger, older females exhibited longer spawning periods and higher batch fecundities, but neither greater spawning frequency nor egg dry weight. The ratio of the effective to predicted reproductive lifespan at maximum sustainable yield was 31%. Many parameters estimated in this study are common to fish reproductive studies, but we hope that inte- grating them into a reproductive resilience framework will help focus the need for research on the underlying relationships between reproductive traits and stock productivity.

Estimating fecundity in the zygoparous species Helicolenus dactylopterus (Actinopterygii, Scorpaeniformes): adaptation of the gravimetric method

Bluemouth, Helicolenus dactylopterus is zygoparous species with internal fertilization spawning multiple batches of early-celled embryos in gelatinous masses. Its unusual reproductive strategy required methodological adjustments to estimate potential annual fecundity. The present study applied an adaptation of the gravimetric method, estimated batch fecundity based on different spawning fraction criteria (gestation, early-celled, and blastula females), and compared these estimates with the number of developing oocytes (NDOR) in the beginning of spawning to clarify the oocyte development pattern. Spawning fraction estimation based on the gestation criterion was considered the most reliable given its low variance and the subjectivity of staging early-celled embryos. On average, 87 batches were spawned with a mean spawning interval estimated at 1.73 days, and a mean relative annual total fecundity of 1,773 embryos g−1 carcass. The inexistence of a clear decreasing trend in the NDOR throughout the spawning season, and the lower NDOR estimates in females in the beginning of spawning comparing with relative annual fecundity (gestation criterion) suggests vitellogenic oocyte recruitment supporting previous results of indeterminate fecundity in Portuguese coast. The method proposed can be considered in fecundity studies of other commercial important species which extrudes gelatinous egg masses.

Reproductive studies of Anchoa marinii Hildebrand, 1943 (Actinopterygii: Engraulidae) in the nearby-coastal area of Mar Chiquita coastal lagoon, Buenos Aires, Argentina

The aim of the present study provides the first results on the reproductive biology of the anchovy, Anchoa marinii, in a nearby-coastal area of Mar Chiquita coastal lagoon, 37º32'00"S 57º19'00"W, Argentina. To perform this, we employed mainly female gonads, at both microscopic and macroscopic levels. The oocyte diameter distribution and the microscopy analysis of oocytes, showed different batches of growing oocytes, suggesting that the anchovy is a multiple spawner, with constant oocytes recruitment all over the reproductive season. The batch fecundity ranged between 749 and 3,207 oocytes for females, and the relative fecundity ranged from 127 to 422 yolked oocytes per female gram (ovary free). The fecundity estimation has been made with yolked oocytes. No correlation between the fecundity estimation and female size and total weight (without ovary) has been found. The estimated L50 values were 74.13 and 73.76 mm TL for females and males, respectively. Shoals of females in advanced maturity phase were recorded, between December to April in the study area. During this period a significant increase of species abundance was correlated with water temperature increase (above 16°C). This fact, together with the detection of post-ovulatory follicles, indicated the existence of reproductive events in the nearby-coastal area of Mar Chiquita coastal lagoon.

Reproductive biology of invasive lionfish (Pterois spp.)

Indo-Pacific lionfishes, Pterois volitans (Linnaeus, 1758) and Pterois miles (Bennett, 1828), native to the Pacific and Indian Oceans, respectively, were first observed in the western Atlantic off Florida in 1985. They have since spread and are established throughout the broader Caribbean region. Despite potentially devastating ecological and economic effects, information on key life history characteristics for lionfish in the invaded range is sparse. Objectives of this study were to quantify 1) periodicity in gonad development and spawning, 2) spawning frequency, 3) batch fecundity and 4) female size at maturity for fish from Little Cayman. Calculation of gonadosomatic indices, histological and macroscopic staging of gonads, and counts of hydrated oocytes were applied to determine reproductive characteristics. Higher gonadosomatic indices were recorded for females during periods of stable warm or cool water temperatures indicating that extreme temperatures did not constrain reproduction. Histological and macroscopic staging suggested that male and female lionfish were capable of reproducing year-round. However, higher gonadosomatic indices in females, as expected before spawning, were most pronounced in March/April and August. Based on the proportion of females containing hydrated oocytes, mature lionfish had the potential to spawn every 2–3 d. Ovaries of mature females contained 1800–41945 oocytes that were hydrated in preparation for spawning, with greater numbers of oocytes in larger females. Female lionfish matured at 189–190 mm total length. Parameters estimated in this study can improve outputs from population dynamic models, which will help resource managers design removals and other efforts to control invasive lionfish.

Intra-population trends in the maturation and reproduction of a temperate marine herbivore Girella elevata across latitudinal clines.

Latitudinal variation in the reproductive characteristics of a temperate marine herbivore, rock blackfish Girella elevata, was examined from three regions of the south-eastern Australian coast. Biological sampling covered 780 km of coastline, including the majority of the species distribution. The sampling range incorporated three distinct oceanographic regions of the East Australian Current, a poleward-flowing western boundary current of the Southern Pacific Gyre and climate-change hotspot. Girella elevata are a highly fecund, group synchronous (multiple batch)-spawner. Mean fork length (LF ) and age at maturity were greater for females than males within all regions, with both male and female G. elevata of the southern region maturing at a greater size and age than those from the central region. Estimates of batch fecundity (FB ) were greatest in the northern and southern regions, relative to the central region where growth rates were greatest. Significant positive relationships were observed between FB and LF , and FB and total fish mass. Gonado-somatic indices indicated latitudinal synchrony in spawning seasonality between G. elevata at higher latitudes, spawning in the late austral spring and summer. A late or prolonged spawning period is evident for G. elevata from the northern region. Juvenile recruitment to intertidal rock pools within the central and southern regions was synchronous with the spawning season, however, no juveniles were found within the northern region. The implications of latitudinal variation in reproductive characteristics are discussed in the context of climate and oceanographic conditions of south-east Australia.

Oogenesis and Fecundity Type of Gray Triggerfish in the Gulf of Mexico

AbstractThe fecundity of Gray Triggerfish Balistes capriscus has been difficult to estimate, as few imminently spawning or recently spawned females have been detected. Our study focused on verifying the pattern of oogenesis and fecundity type in Gray Triggerfish. During 1999–2012, females (n = 1,092) were collected from the eastern Gulf of Mexico, and subsets of these fish were used to calculate condition indices and assess ovarian histology. The gonadosomatic index, hepatosomatic index, and Fulton's condition factor indicated that liver and somatic energy stores increased prior to spawning and were depleted throughout the spawning period, characteristic of a capital pattern of energy storage and allocation to reproduction. Typical of a capital breeding pattern, we also observed (1) a hiatus in oocyte size distribution and (2) group‐synchronous oogenesis, which are both traits of a determinate fecundity type. However, evidence that fecundity was not set prior to spawning included the observation of “de novo” vitellogenesis during the spawning season; secondary oocytes increased in number and failed to increase in mean size over time. Thus, Gray Triggerfish exhibit an indeterminate fecundity type with mixed reproductive traits that may characterize species exhibiting female parental care in warmwater environments. Further, we estimated the secondary oocyte growth rate (37 m/d) based upon the time lag of postovulatory follicle (POF) degeneration. Using oocyte growth rate and the proportion of females bearing POFs, the interspawning interval was estimated to range from 8 to 11 d, indicating that 8–11 batches/female could be produced during the estimated 86‐d reproductive period. The hiatus in oocyte size distribution was used to define a minimum size (250 m) from which to distinguish an advancing batch of secondary growth oocytes. Batch fecundity (BF) ranged from 0.34 to 1.99 million eggs and was significantly related to FL (mm): BF = 8,703.69·FL – 1,776,483 (r2 = 0.56).Received October 10, 2014; accepted June 27, 2015

The First Spontaneous Spawning of Red Drum Sciaenops Ocellatus L. in Europe: Broodstock Management and Early Larval Stages

The present paper reports a research on reproductive parameters and larval rearing of red drum (Sciaenops ocellatus) maintained in captivity for the first time in Europe. Red drum juveniles were obtained from United States in the late 90s. In early January 2013, 40 in total male and female red drums ranging from 34 to 47 cm in length were held in a 25 m3 rectangular tank with a closed recirculating system with a water flow of 6000 L/h, located in Lesina (FG) fish farm (Southern Italy). Water temperature and salinity ranged between 21.0 and 28.8°C and from 25 to 27 g/L respectively. The fish were fed commercial feed pellet (46% protein) at 1.1% of body weight daily. Sexual maturation occurred during the natural breeding season of red drum. Approximately 43 spawns were recorded by the end of July and continuing to mid-September, with mean number of 66.5 millions of eggs collected overall on spawn period. Batch fecundity (3.325*106 ova per female) and relative fecundity (361.41 ova/g body weight) were calculated. Fertilisation rate was 30 to 80%. Larvae were hatched at a mean total length of 2.40±0.33 mm and showed a gradual increase in size of approximately 0.378 mm/day for the first 40 day after hatching (DAH). Cannibalism was observed as larger larvae preyed on smaller ones; to limit the phenomenon red drum population was selected for size at 35 DAH. Reliable information on fecundity and larval stage is essential for encouraging Sciaenops ocellatus farming also in Mediterranean countries.

Fish egg size: a characteristic determined by parental care

Fish egg size: a characteristic determined by parental care

Temperature- and income resource availability-mediated variation in reproductive investment in a multiple-batch-spawning Japanese anchovy

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 516:251-262 (2014) - DOI: https://doi.org/10.3354/meps10969 Temperature- and income resource availability-mediated variation in reproductive investment in a multiple-batch-spawning Japanese anchovy Michio Yoneda1,*, Hajime Kitano2, Hiroshige Tanaka3, Kohei Kawamura4, Sethu Selvaraj4, Seiji Ohshimo5, Michiya Matsuyama4, Akio Shimizu6 1National Research Institute of Fisheries and Environment of Inland Sea, Hakatajima Station, Imabari 794-2305, Japan 2Fisheries Research Institute of Karatsu, Department of Joint Research, Faculty of Agriculture, Kyushu University, Karatsu 847-0132, Japan 3Hokkaido National Fisheries Research Institute, Kushiro 085-0802, Japan 4Laboratory of Marine Biology, Department of Bioresource Sciences, Faculty of Agriculture, Kyushu University, Fukuoka 812-8581, Japan 5National Research Institute of Far Seas Fisheries, Shizuoka 424-8633, Japan 6National Research Institute of Fisheries Science, Fukuura, Yokohama 236-8648, Japan *Corresponding author: myoneda@fra.affrc.go.jp ABSTRACT: Multiple batch spawning over a season should have an advantage for maternal fitness in unpredictable environments, but the manner in which females allocate resources to reproduction is not well understood. We explored the effects of temperature and food availability on reproductive traits in Japanese anchovy Engraulis japonicus using several physiological analyses. Under ad libitum food availability, temperature had a significant effect on batch intervals by changing the growth rate and size of oocytes during vitellogenesis. The latter is likely to result in variations in the size and total nutritional content of eggs. Relative batch fecundity, however, was not significantly influenced by temperature regimes. Reproductive effort per spawning was significantly higher at lower temperature, caused by the production of eggs with higher nutritional content, while total reproductive effort in a given period of time increased in water at a higher temperature due to shortening of batch intervals. Short-term food manipulation also had a significant effect on reproductive output. Insufficient income resources could lead to prolonged batch intervals, but the relative batch fecundity remained constant independent of the temperature regime. Our findings suggest that female Japanese anchovy may maintain reproductive effort per spawning relative to the prevailing temperature at the expense of more spawning events in a nutritionally harsh environment. Thus, although the total reproductive effort of well-fed specimens increased in water with increasing temperature due to shortened batch intervals, this variation may be caused by a compensatory response to the level of income resources available. KEY WORDS: Engraulis japonicus · Phenotypic plasticity · Energy allocation · Reproductive effort · Batch interval · Egg size · Egg production Full text in pdf format Supplementary material PreviousNextCite this article as: Yoneda M, Kitano H, Tanaka H, Kawamura K and others (2014) Temperature- and income resource availability-mediated variation in reproductive investment in a multiple-batch-spawning Japanese anchovy. Mar Ecol Prog Ser 516:251-262. https://doi.org/10.3354/meps10969 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 516. Online publication date: December 03, 2014 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2014 Inter-Research.

Variations in reproductive potential between nearshore and offshore spawning contingents of hogfish in the eastern Gulf of Mexico

Hogfish, Lachnolaimus maximus (Walbaum), have multiple traits that confound measuring reproductive potential: they are protogynous, relatively long-lived harem-forming fish that spawn daily for months. Additionally, recent evidence demonstrates that size, age and timing of sex change vary on a spatial scale within the study area (West Florida shelf, USA). This study investigates the effect of this spatial variation on hogfish reproductive potential by evaluating spawning seasonality, spawning frequency and batch fecundity using an indeterminate egg production model. Offshore females were larger than nearshore females, and batch fecundity was related in a log-linear manner to female size. Gonad histology demonstrated a more protracted reproductive period for females offshore (8 months) than nearshore (4 months). Spatial variations in size coincide with ontogeny because hogfish move offshore with growth; however, even after accounting for fish size, offshore females spawned more. In areas where male removal rates are elevated, spawning harems are disrupted; thus, greater fishing effort nearshore may further reduce the reproductive potential of these females. These nearshore and offshore spawning components of the population are not genetically distinct, but instead represent two contingent spawning strategies that likely enhance total population stability and resilience of this stock in the eastern Gulf of Mexico.

Reproductive biology of the black marlin, Istiompax indica, off southwestern and eastern Taiwan

The reproductive biology of the black marlin, Istiompax indica, was assessed by examining 4762 fish (458 ovary samples) caught by offshore longliners off southwestern and eastern Taiwan during 2004–2007. The overall sex ratio (0.67 off southwestern and 0.86 off eastern Taiwan) was significantly different from 0.5 (p<0.01), with females predominant in both sampling areas. Monthly variation in the gonadosomatic index, mean monthly oocyte diameter, and histological analysis indicated that black marlin spawned off southwestern Taiwan during March and April. Although black marlin aggregated for feeding purposes off eastern Taiwan, no evidence of spawning was found in samples from this location. The size-at-50% maturity was estimated at ∼195cm eye-to-fork-length (EFL) (∼5.4 years old) for female black marlin. Fully mature female black marlin were estimated to spawn once every ∼2.8 days using the hydrated oocyte method. Batch fecundity was estimated from 19 females, and varied 10-fold from 3.2 to 32 million eggs, with an average of 15.2±1.9 (±S.E.) million eggs. The average relative batch fecundity was estimated at 105.7±12.0 (±S.E.) eggs per gram of body weight. The relationships between batch fecundity (BF, million eggs), EFL and round weight (i.e., whole fish weight; RW, kg) were BF=2×10−12EFL8.05 (r2=0.43) and BF=8×10−4RW1.95 (r2=0.37), respectively. The parameters estimated in this study are key information for stock assessments of black marlin in the western Pacific Ocean and will contribute to the management, conservation and sustainable yield of this species

Reproductive condition, batch fecundity, and spawning fraction of large Pacific bluefin tuna Thunnus orientalis landed at Ishigaki Island, Okinawa, Japan

In order to illustrate the reproductive activity of Pacific bluefin tuna (Thunnus orientalis) around the Yaeyama archipelago, an area known to be the species’ major spawning ground, gonadal condition of large individuals obtained by longline fishing was assessed during the commercial fishery season between late April and early July in 2008 and 2009. Almost all of the specimens landed at Ishigaki Island during these two seasons were larger than 200 cm in fork length (FL), and, while the sex ratio was nearly 1:1 in total, a significant bias existed towards males when only individuals with FL values greater than 230 cm were considered. All females were sexually mature and sperm was observed in the testes of all males throughout the fishing season. Average spawning intervals (fraction) and average batch fecundity (mean ± SD) were estimated at 3.29 days (0.30) and 15.4 ± 10.2 million oocytes, respectively. Ovarian and testicular maturation phase based on histological assessment did not show any significant changes over the two-year study period, while commencement of spawning varied from year to year. We determined that spawning activity of Pacific bluefin tuna around the Yaeyama archipelago persisted throughout the fishing season, and likely varied due to the annual fluctuations in environmental conditions at the spawning ground.

REPRODUCTIVE BIOLOGY OF THE BOMBAY-DUCK HARPADON MICROCHIR IN THE COASTAL WATERS OFF SOUTHWESTERN TAIWAN

The bombay-duck, Harpadon microchir, is one of the important bycatch species of the trawl fishery in the waters off southwestern Taiwan. However, its biological information, especially reproductive biology, is still lacking. In this study, the reproductive biology of the bombay-duck was described based on 1,697 specimens (1,066 females and 631 males) caught by bottom trawl fishery in the waters off southwestern Taiwan from October 2007 to December 2008. The spawning season of this species was estimated to be in May and from August to December with a peak in November based on the macroscopic appearance, gonadosomatic index, histological examination, and group maturity rate. Oocyte development and ovarian development were categorized into nine stages and four stages, respectively based on histological or macroscopic examination. Mean fecundity and mean batch fecundity were estimated to be 446,373 ± 174,858 and 61,680 ± 60,279, respectively. The relationship between fecundity (F) and body weight (BW) was estimated as: F = −46.580 + 9.69 × 10 3 BW(r 2 = 0.587; n = 50). The sex ratio (female/total), 0.63, was significantly different from 0.5. The sizes at 50% maturity were estimated to be 39.9 and 19.8 cm FL for females and males, respectively.

Stock-recruitment resilience of North Pacific striped marlin based on reproductive ecology

The resilience of a stock-recruitment relationship is a key characteristic for modeling the population dynamics of living marine resources. Steepness determines the expected resiliency of a fish stock to harvest and is fundamentally important for the estimation of biological reference points such as maximum sustainable yield. Stock-recruitment steepness was the primary uncertainty for the determination of stock status and biological reference points in recent stock assessments of Western and Central North Pacific striped marlin (Kajikia audax). We therefore applied the method of Mangel et al. to estimate probable values of steepness for striped marlin using new information on the mean batch fecundity, spawning frequency, and spawning season duration under an assumption of Beverton–Holt stock-recruitment dynamics. Results indicated that the median steepness was 0.87 with an 80% probable range of (0.38, 0.98). It is very likely that North Pacific striped marlin is highly resilient to reductions in spawning potential. Variation in reproductive and life history parameters had an important influence on the distribution of steepness. Sensitivity analyses showed that steepness was most sensitive to body girth, mean egg weight, and most importantly, early life history stage survival. Sensitivity analyses also confirmed that the effects of changes in life history parameters on steepness were consistent with expected increases or decreases in reproductive output due to changes in body weight or fecundity. Our approach can be applied to pelagic fish species to directly assess the probable distribution of stock-recruitment resiliency when sufficient information on reproductive ecology and life history parameters is available.

Reproductive biology of the lane snapper, Lutjanus synagris, and recommendations for its management on the Abrolhos Shelf, Brazil

The reproductive biology of the lane snapper, Lutjanus synagris, was evaluated from 770 specimens (434 females and 336 males) obtained on the Abrolhos Bank, eastern Brazil, between May 2005 and October 2007. Total length ranged from 14.7 to 56.0 cm for females and from 16.5 to 54.3 cm for males, with size composition not varying significantly between sexes. Five distinct maturity stages were identified based on macroscopic and histological examination of the gonads. Mean value of the gonadosomatic index (GSI) for females peaked in September and October, with a secondary peak in February and March. Histological analyses confirmed the reproductive cycle inferred by GSI variation. Asynchronous-type ovarian development was observed, and batch fecundity ranged from less than 104,743 oocytes for a 25.5 cm female of to 568,400 oocytes for a 56.0 cm female (250.0 and 2260 g, respectively), with an average of 345,700 oocytes. The reproductive parameters obtained for L. synagris in the Abrolhos Bank were similar to those reported in studies in northern Brazil and the north-west Atlantic. The species is an important fishery resource in the study region, and management measures are needed before the species becomes overfished. Exploitation occurs largely during spawning aggregations, a situation that has caused other lane snapper populations (and congeners) to decline acutely elsewhere. Our results provide support for size limits and seasonal spawning closures on the Abrolhos Bank, a region that sustains artisanal fisheries involving &gt;20,000 fishermen.

Depth interactions and reproductive ecology of sympatric Sillaginidae: Sillago robusta and S. flindersi

This study examined whether differences existed in the depth distributions and reproductive strategies of the co-occurring Sillago robusta and S. flindersi in coastal waters off eastern Australia. Marked spatial and temporal dissimilarities in demography and reproduction were observed between the 2 species, with S. robusta being more abundant in the shallow (15�30 m) strata and S. flindersi in the mid (31�60 m) strata, with neither species being consis- tently abundant in the deep (61�90 m) strata. The size composition of S. robusta was similar across depths, but smaller and immature S. flindersi predominantly occurred in the shallow strata, with larger and mature individuals occurring deeper. These data indicate partitioning of habitat resources, which may aid species coexistence. Both species potentially spawned year-round, which is probably an adaptation to the region's dynamic coastal environment. However, a greater proportion of S. robusta was in spawning condition between September and March, whereas S. flindersi displayed no such temporal pattern. Maturity ogives differed significantly between sexes and locations for both species. Both species displayed similar ovarian development, with females having multiple concurrent oocyte stages, indicating potential multiple spawning events as evidenced in other Sillaginidae. For both species, estimated batch fecundity increased with fish length, but S. robusta had a greater fecundity at any given length than S. flindersi. In contrast, S. flindersi potentially produced larger-sized eggs and invested greater energy into gonad devel- opment than S. robusta, indicating the 2 species have evolved slightly different reproductive strategies. Despite this, both species are subjected to substantial trawl fisheries, which may have already impacted their reproductive ecologies.

Stereological comparison of oocyte recruitment and batch fecundity estimates from paraffin and resin sections using spawning albacore (Thunnus alalunga) ovaries as a case study

Traditional histological protocols in marine fish reproductive laboratories using paraffin as the embedding medium are now increasingly being replaced with protocols using resin instead. These procedures entail different degrees of tissue shrinkage complicating direct comparisons of measurement results across laboratories or articles. In this work we selected ovaries of spawning Mediterranean albacore (Thunnus alalunga) as the subject of our study to address the issue of structural changes, by contrasting values on oocyte recruitment and final batch fecundity given from the same tissue samples in both paraffin and resin. A modern stereological method, the oocyte packing density (OPD) theory, was used supported by initial studies on ovarian tissue sampling and measurement design. Examples of differences in the volume fraction of oocyte stages, free space and connective tissue were found between the embedding media. Mean oocyte diameters were smaller in paraffin than in resin with differences ranging between 0.5% in primary growth and 24.3% in hydration (HYD) stage oocytes. Fresh oocyte measurements showed that oocytes shrank as a consequence of the embedding process, reaching the maximal degree of shrinkage for oocytes in the HYD stage (45.8% in paraffin and 26.5% in resin). In order to assess the effect of oocyte shrinkage on the OPD result, and thereby on relative batch fecundity (Fr), oocyte diameters corrected and uncorrected for shrinkage, were used for estimations. Statistical significant differences were found (P<0.05) between these two approaches in both embedding media. The average Fr was numerically smaller in paraffin compared to resin (86±61 vs. 106±54 oocytes per gram of body mass (mean±SD)). For both embedding media statistical significant differences (P<0.05) were seen between Fr results based on either oocytes in the germinal vesicle migration stage or HYD stage. As a valuable adjunct, the present use of the OPD theory made it possible to document that the oocyte recruitment of spawning ovaries of Mediterranean albacore followed the typical pattern of an asynchronous oocyte development and indeterminate fecundity.

Reproductive timing and reproductive capacity of the Skipjack Tuna (Katsuwonus pelamis) in the western Indian Ocean

We studied the sexual maturity, batch fecundity and spawning season of the Skipjack Tuna Katsuwonus pelamis. Generalized additive modelling was applied to assess the effect of demographic features on ovary growth. During 2009 and 2010, 673 females were caught on board a purse-seine fishing vessel in the western Indian Ocean. Fish were classified into different reproductive phases and this information was used to determine the size at maturity (L50), the timing of spawning and the batch fecundity (n=51). The size at maturity (L50) for females was estimated to be 39.9cm. The mean relative batch fecundity was 140±64 eggs g−1 of fish. Spawning occurs during the monsoons and inter-monsoon seasons with peaks in the reproductive activity during the North-east and South-west monsoon events. Demographic differences were detected in the reproductive timing of the population and a large investment in gamete production was observed in fish with high hepatic condition and in their first spawning year.