Batch fecundity of Atlantic mackerel, Scomber scombrus L.

The total annual fecundity of mackerel, Scomber scombrus L., during a spawning season is produced by release of discrete batches of eggs. Total fecundity is then the product of the number of batches times the batch fecundity ( F _bw). An extensive trawl survey of the Western mackerel stock in the NE Atlantic was undertaken in the 1989 spawning season. Batch fecundity was estimated for 298 fish by counting hydrated eggs in ovaries just prior to ovulation. F _bw, expressed as eggs g⁻¹ body weight, varied with latitude: south of 51°N, F _bw= 55.49, s.e. = 2.04, n = 227; between 51°N and 55°N, F _bw= 45.72, s.e. = 3.41, n = 52 and north of 55° N, F _bw= 41.33, s.e. = 5.52, n = 19. It is suggested that as spawning fish migrate northwards the batch size decreases with progress of the spawning season.     

Influence of seasonal changes in relative liver size, condition, relative gonad size and variability in ovarian development in multiple spawning fish species used in environmental monitoring programmes

Basic biological information was collected to assist in understanding the biology of selected small-bodied fishes for use in environmental monitoring programmes. Gonado-somatic index ( I _G) and hepato-somatic index ( I _H) profiles of female blacknose dace Rhinichthys atratulus , mummichog Fundulus heteroclitus and golden shiner Notemigonus crysoleucas were similar, decreasing gradually during the spawning season. I _G and I _H profiles of female northern redbelly dace Phoxinus eos peaked twice suggesting oocyte recruitment was continuous throughout the spawning season. Regressions of ovary mass to adjusted body mass ( M _A) were more variable in dace relative to the other fish species. For female blacknose dace, variability in the relationship between ovary mass and M _A was minimized by selecting either 2 year-old fish and fish that weighed 2–4 g.     

Stereological assessment of the reproductive status of female Atlantic northern bluefin tuna during migration to Mediterranean spawning grounds through the Strait of Gibraltar

The ovarian mass and gonadosomatic index (I_G) of bluefin tuna Thunnus thynnus , caught in the Strait of Gibraltar (Barbate) during migration to Mediterranean spawning grounds, were several times lower than those found in bluefin tuna from Mediterranean spawning grounds (Balearic Islands). Some of the bluefin tuna from Barbate (8.3%) were classified as immature (the most advanced oocytes present in the ovaries were early vitellogenic), and the majority (the remaining 91.6%) as non-spawning mature; the ovary contained late vitellogenic oocytes, but there was no sign of spawning activity. Stereological estimation indicated that the ovaries of spawning bluefin tuna from the Balearic Islands contained five-fold more highly yolked oocytes than bluefin tuna from Barbate. When breeding bluefin tuna cross the Strait of Gibraltar the gonad is at an incipient stage of maturation. The average batch fecundity estimated from stereological quantification of stage 4 (migratory-nucleus) oocytes in the specimens collected from Balearic was 92.8 oocytes g-1'of body mass, and the spawning frequency in this area was calculated to be 1.2 days. In specimens from Barbate a relative batch fecundity of 96.3 oocytes g -1 was estimated using stage 3 (late vitellogenic) oocyte counts.     

Reproductive biology of the endangered Oxleyan pygmy perch Nannoperca oxleyana Whitley

The reproductive biology of the Oxleyan pygmy perch Nannoperca oxleyana is described from simultaneous studies of wild populations in north-eastern New South Wales and mature fish held in aquaria. In the wild, 50% of males and females matured at total lengths of 24·0–25·9 and 28·0–29·9 mm, respectively. The species displays sexual dichromatism during the spawning season, with males developing more intense red and brown fin and body colouration, and black pelvic fins. Captive male broodfish displayed territoriality during the breeding season, closely guarding sites within artificial, plant-like substrata in which pairs of fish spawned adhesive eggs. Protracted serial spawning of wild and captive fish occurred from September to April and May at mean water temperatures ≥16·6° C and day length ≥10·7 h. Captive broodfish spawned on an average of 57% of days during the 256 day spawning period. Gonado-somatic indices averaged 0·7% for all ripe males and 4·1–4·2% for all ripe females collected. Mean total and batch fecundities of captive females were 1323 eggs per fish and 7·8 eggs per fish per day, respectively, and relative fecundity was 587 eggs g⁻¹ of body mass. Batch fecundity of wild females was estimated at 7·8 eggs per fish. The adaptive significance of this reproductive strategy in a harsh, variable environment is discussed.     

Influence of female age, body size and environmental conditions on annual egg production of the bullhead

A population of bullhead Cottus gobio inhabiting a mountainous river network, was examined for the influence of maternal condition (total length, L _T, and age class in years) and environmental factors (water temperature and fish density) on fecundity, egg size and net annual reproductive effort ( E _R, defined as the ratio of total egg production mass to body mass) within several stocks. Regardless of location within the drainage network, bullhead reproduction was synchronous, with only a single batch and fecundity ranging from 69 to 896 eggs per female. As with L _T fecundity increased with age, although the difference between age classes 5 and 6 years was smaller than between other age classes. Egg diameter also increased with age from age classes 2 to 4 years, but then tended to decrease for age classes 5–6 years. Multiple stepwise regression was used to examine the effect of female L _T, water temperature and fish densities on bullhead egg production for each of the four age classes (2, 3, 4 and 5–6 years) separately. When statistically significant, water temperature always had a positive effect and fish densities a negative effect, on fecundity and egg size. The L _T always had a positive effect on fecundity for all the age classes. In contrast, L _T had a positive effect on egg size and E _R only for female reaching maturity (2 years), whereas intermediate aged females (3–4 years) were insensitive and the oldest fish showed a negative response.     

Trade-off between egg mass and egg number in brown trout

Individual egg mass and fecundity increased with somatic mass in first time and repeat spawning wild anadromous and freshwater resident brown trout Salmo trutta . The egg mass was larger for similar-sized trout in south (58° N) than mid Norway (63° N), whereas fecundity was higher in mid- than in south Norway, making total gonadal investment similar in the two areas. Repeat spawners had heavier eggs than similar-sized first time spawners. The egg mass of residents was c. 10% larger than that of similar-sized first time spawning anadromous trout. Common garden experiments with offspring of wild anadromous trout showed no significant correlation between egg and somatic mass in first time spawners in two of the three populations studied. In the third population, a slight positive correlation was found. Similar results were found for repeat spawners. In the three populations, fecundity increased significantly with somatic mass in both first time and repeat spawners. Wild and hatchery-reared trout showed negative correlation between egg mass and fecundity when the effect of body size was excluded, indicating a trade-off between the two parameters. In wild trout, this was caused by variation among populations, whereas in hatchery fish, within population variation was observed in egg mass over fecundity. Furthermore, the egg mass of first time and repeat spawners were positively correlated, when adjusted for fish size. Size-specific gonadal investment was significantly higher in wild anadromous than resident trout. There was no significant difference in gonadal investment between first time and repeat spawners in wild anadromous trout. However, in the hatchery-reared trout, gonadal investment was significantly higher at repeat than first time maturation. The hatchery trout did not spawn naturally, but were artificially stripped. Among populations, a part of the variation in egg mass and fecundity is phenotypically plastic, a part appears genetically determined.     

Spawning frequency, fecundity, egg weight and spawning type of silver pomfret, Pampus argenteus (Euphrasen) (Stromateidae), in Kuwait waters

Silver pomfret, Pampus argenteus, were collected by fishing with drift gillnets on one spawning ground in Kuwait waters during 1998–2000. Fish size frequency, sex ratio, maturation cycle, spawning frequency, fecundity and egg weight were assessed. The length–weight relationship differed between sexes whereby females were significantly bigger than males. Spawning started in mid‐May and continued until early October. During this time the water temperature ranged from 26.0 to 32.8°C, salinity was ? 39.0‰ and water depth ranged between 5 and 12 m. Large females spawned earlier than young spawners and the overall percentage of males during the spawning period was 70.3%. Spawning occurred after 13.00 h, with peak spawning between 15.00 and 18.00 hours during outgoing tide. Mean daily spawning frequency amounted to 63.2%. Spawning activity was found to be associated with the lunar cycle and spawnings were concentrated during the first and third quarters of the moon period, indicating a semilunar reproduction cycle. It was concluded that a female would spawn at least six times during the season. No change was observed in relative fecundity during the peak spawning season (June–August). Average relative batch fecundity was 176.3 eggs g^?1 somatic weight (SW), corresponding to a relative total fecundity of 1058 eggs g^?1 SW, which is 1.5 times higher than estimates obtained from counting the standing stock of oocytes. Bigger fish produced heavier eggs and the egg weight decreased as the spawning season progressed. Based on gonadal cycles, oocyte size frequency distribution and total fecundity, we concluded that silver pomfret is a multiple batch spawner with indeterminate fecundity.     

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.     

Effects of fish size on spawning time in Norwegian spring-spawning herring

During October-January in a northern Norwegian fjord system and in February-March at the main western Norway spawning grounds, an index I _G of gonad weight of spring-spawning herring Clupea harengus in percentage of expected gonad weight at full maturity for a given total length L _T, tended to increase with L _T in the range 27–31 cm as the proportion of recruit spawners decreased. Insignificant differences in I _G were found between L _T groups in the range 32–37 cm (repeat spawners). This is contrary to that suggested in other studies and signifies that generally the stock spawns in only two waves, repeat spawners first and the recruit spawners second. I _G also increased with somatic and total condition factor, which signifies that spawning time may be influenced by summer feeding conditions.     

鱼类分批繁殖力和繁殖频率的研究进展

繁殖潜力是决定鱼类的繁殖补充及制定种群评估生物学假设的关键机制,由此分批繁殖力和繁殖频率对评估分批繁殖鱼类的繁殖潜力就十分必要.分批繁殖力和繁殖频率的研究均开始于20世纪80年代,在过去的30年中,评估分批繁殖力最为广泛使用的方法是水化卵法,而繁殖频率使用最多的方法是产后滤泡法.这两种方法虽然都存在一定的不足,但无可否认是现在最为实用和成熟的方法.     

Regional and interannual variations in spawning activity of Pacific saury Cololabis saira during northward migration in spring in the north-western Pacific

Regional and interannual variations in spawning activity of Pacific saury Cololabis saira during the northward migration in spring were investigated for 1995–1997 in the north-western Pacific. Only females with a large body size (≥270–290 mm knob length) appeared to spawn. Almost all females in this cohort were actively spawning in a region of sea surface temperature ( T _SS) >18° C, the proportion of active spawners appeared positively related to T _SS in a region of 13° C < T _SS≤ 18° C, and no females were spawning in the region of T _SS≤13° C. Although this relationship between spawning activity and T _SS was common in all years, the distribution of females in the large-size cohort among the regions varied interannually. Consequently, the proportion of active spawners among adult females showed considerable interannual variations.     

Effects of fasting on temporal changes in plasma concentrations of sex steroids, growth hormone and insulin‐like growth factor I, and reproductive investment in Arctic charr

Proportions of maturing fish and reproductive output [egg size, relative fecundity, spermatocrit and gonado‐somatic index ( I _G)] were studied in repeat‐spawning (+4 year old) male and female Arctic charr Salvelinus alpinus , subjected to periods of fasting. Groups of individually tagged Arctic charr were fasted for c . 3, 6, 7 and 9 months, from November 1998. In the period February to November 1999, size (fork length and mass), specific growth rate ( G ), condition factor ( K ) and plasma concentrations of growth hormone (GH), insulin‐like growth factor I (IGF‐I), oestradiol‐17β(E₂; females) and 11‐ketotestosterone (11KT; males), were monitored monthly. Maturing fish in each group started to gain mass soon after food was made available, and both sexes reached the highest K and G c . 2 months after the onset of feeding. The fasting regimes resulted in different growth patterns during spring and summer when energy stores are normally replenished in Arctic charr, and K prior to the breeding season was significantly higher in the groups fasted for 3 and 6 months compared to the groups fasted for 7 and 9 months. There were significant positive correlations between K during the period prior to the breeding season and reproductive output in terms of the I _G, spermatocrit and relative fecundity. There was, however, no clear relationship between the length of starvation and the proportion of maturing fish. Likewise, no clear relationships were found between reproductive development and plasma levels of GH and IGF‐I, although both showed marked seasonal changes, being 'down‐regulated' during winter months and 'up‐regulated' throughout summer months.     

Size-specific spawing pattern in ayu,Plecoglossus altivelis

The spawning pattern and relationship to body size at maturation of amphidromous and land-locked forms of ayu,Plecoglossus altivelis, was investigated. Ovarian eggs of prespawning females showed a multimodal size distribution, regardles of body size, indicating that all the females were potentially a batch spawners. The spawning schedules of individual fish were described under simulated spawning conditions. Most large-sized females died soon after their first spawning, whereas approximately half of the medium and small-sized females successfully completed a second spawning some two weeks after the first. Such a size-specific spawning pattern was common to both forms, but development of a third batch of ovarian eggs after the second spawning occurred only in the land-locked form. Spawning tactics in ayu were related to offspring survival and adult mortality during spawning season.     

Variability in condition and growth of Atlantic cod larvae and juveniles reared in mesocosms: environmental and maternal effects

Standard length, dry mass and RNA : DNA ratio measurements of 3876 Atlantic cod Gadus morhua larvae and juveniles from 26 families of recruit (fish during their first year of spawning) and repeat spawners (fish which were in their subsequent spawning season) reared in two mesocosms (2500 and 4400 m³) under semi-natural conditions were analysed over a period of 10 weeks using microsatellites. Larvae from recruit spawners were significantly longer and heavier at hatch and throughout the 10 weeks. RNA : DNA ratios from recruit spawner offspring were only significantly higher at week 1. The smaller (2500 m³) mesocosm was characterized by low plankton density during the transition from endogenous to exogenous feeding followed by a higher density during the metamorphosis period (weeks 4 and 5), with the reverse pattern evident in the 4400 m³ mesocosm. Patterns of larval growth followed patterns of zooplankton density. Significant differences in RNA : DNA ratios between the mesocosms at all comparable sampling dates were found and within each mesocosm individual fish exhibited a wide range of growth and condition responses under the same environmental conditions. RNA : DNA ratios as a function of size differed in the amount of variability between mesocosms, indicating that the higher food density led to a higher proportion of well-conditioned larvae in the first 3 weeks. Food availability probably has a major role in determining offspring growth and condition, with limited effects due to maternal effects in cases where the broodstock females are approximately of similar size and condition.     

The influence of maternal length and age on the size and weight of the eggs and the relative fecundity of the haddock, Melanogrammus aeglefinus, in British waters

The diameter and dry weight of the eggs of haddock, Melanogrammus aeglefinus , are positively correlated with fish length. The correlations are largely due to the fact that many of the smaller fish that were sampled were 2 years old, and the eggs of these young haddock, which can be regarded as precocious spawners, are significantly smaller and lighter than those of older fish. The relative fecundity of 2–year–old haddock (274 eggs g⁻¹) is also lower than that of the other age classes (493 eggs g⁻¹); this has important implications for the estimation of egg production from female spawning stock biomass. It is pointed out that in some years precocious spawners represent a large component of the North Sea haddock spawning stock. When the annual egg production of this stock is calculated, it may be appropriate to apply a weighting factor to the number of eggs contributed by the 2–year–olds, on the assumption that the small eggs of these fish produce larvae that are less viable than those of older haddock.     

Ovarian structure and batch fecundity in Lophiomus setigerus

The ovarian structure and batch fecundity of anglerfish Lophiomus setigerus were examined from specimens collected in the East China Sea during March 1991 to September 1995. The right and left ovarian lobes were connected at their posterior ends. Stalk-like ovigerous lamellae protruded from the ovarian wall. During the spawning season, gelatinous material was secreted from the epithelia of both the ovigerous lamellae and ovarian wall, and these epithelia showed morphological changes accompanying the ovarian maturation cycle. Tertiary yolk, migratory nucleus, and mature stage oocytes occurred in the ovaries between May and November, when females with postovulatory follicles and developing vitellogenic oocytes were collected also. These results suggested an extended spawning season during which females undergo repeated spawnings. When the most advanced oocytes attained the secondary yolk stage, they formed a batch that separated from the adjacent group of smaller oocytes. Batch fecundity ( F ) in 20 females with secondary yolk stage ovaries was related to total length (L_T, mm) as F= 556.2 L_T^1.157 (300≤L_T≤396).     

Comparison of various potential fecundity models for north-east Arctic cod Gadus morhua, L. using oocyte diameter as a standardizing factor

To build a better data foundation for recruitment models of north-east Arctic cod Gadus morhua the construction of fecundity models reflecting variation in the nutritional status of the fish was attempted. The models were based on fecundity time series covering 9 years within the period 1986–2004 and included both general and year-specific approaches. Initial data analysis revealed that the potential fecundity ( F _P) (standing stock of vitellogenic oocytes) was significantly reduced as the vitellogenic oocytes increased in size towards the start of spawning. Histological examination strongly indicated that this seasonal reduction was caused by atresia. Regression analysis showed that the F _P was positively correlated to fish total length ( L _T) and the Fulton's condition factor ( K ). A multiple regression including data for all years using fish L _T, K and mean oocyte diameter ( D _O) as independent predictors described the F _P with an r ²= 0·94. This was considerably higher than comparable univariate L _T or mass-based regressions. These univariate regressions had fairly high r ² values when split by years, but not as high as found for year-specific multiple regressions. An important application for individual-based fecundity models may be to generate outputs that can be fed into stock level fecundity and recruitment models. Overall, the multivariate models seemed to be the most accurate. The multivariate model including mean D _O, however, also had the potential to correct for maturity and thus provide unbiased fecundity comparisons between years, stocks and locations.     

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.     

Reproduction mode of European Bitterling (Rhodeus amarus,Bloch, 1782) determined through rapid oocyte counts and size determination using digital imaging

This study focuses on assessing the reproduction mode of an important model species for evolutionary and behavioural ecology by using digital image analysis: the European bitterling Rhodeus amarus (Bloch, 1782). Specifications of mode of reproduction were determined using oocyte size distribution, seasonal dynamics in mean oocyte diameter and total number of oocytes in ovary samples gained from April to July 2007. The rapid oocyte count was enabled by using lucia image analysis software, which also provided measurement and colour estimations of oocytes. Bitterling ovaries showed features typical for indeterminate spawners, i.e. a continuous distribution of oocyte size over the reproductive season and recruitment of new pre‐vitelogenic oocytes in the second half of the reproductive season. These results are consistent with the view that the European bitterling is a batch spawning fish with indeterminate fecundity.     

Seasonal variation in egg production and batch fecundity of European hake Merluccius merluccius (L.) in the Bay of Biscay

Sexually mature female hake Merluccius merluccius with hydrated ovaries were sampled on a monthly basis in the Bay of Biscay, from May 1996 to October 1997 and from March to April 1998. The batch fecundity was positively related to total length. The relative batch fecundity ( F _Brel) varied significantly among months and years, but not between areas, i.e. International Council for the Exploration of the Sea Divisions VIIIa and VIIIb within the Bay of Biscay. Two levels of F _Brel were found in 1997: the highest between January and April (mean ± s . e . 167 ± 5 eggs g⁻¹) and the lowest from May to October (112 ± 3 eggs g⁻¹). Population condition factor and gonado-somatic indices ( I _G) followed the expected trend in relation to the monthly changes in F _Brel during 1997. The F _Brel variation between years was 9% for 1996–1997 and 28% for 1997–1998, and the difference of the I _G was c. 14 and 36%, respectively. Population relative egg production varied from a high value in January to March (985 eggs g⁻¹) to a low egg production between April and October 1997 (445 eggs g⁻¹).