Some aspects of the reproductive biology of Spratelloides gracilis (Schlegel) in the Ysabel Passage, Papua New Guinea

Fecundity, length at first spawning, spawning seasonality and ovarian development of Spratelloides gracilis were determined by examining preserved ovaries from fish captured over a 5-year period. Fecundity ( F ) was estimated from the number of eggs in the most advanced ovarian mode and was related to fish length ( L ) by the function: log_e F =3.764 log_eL-7.308, and to weight ( W ) by: log_eW= 1.210 log_eW+7.337. Spawning was observed in most months of the year without any recognizable pattern between the years. Ova diameter frequencies were bimodal but the smaller mode remained stationary regardless of the position of the larger mode. This was interpreted as evidence that individual fish may spawn only once. From data on egg length versus fish length and gonad index versus fish length it was estimated that fish were first capable of spawning at 45 mm (fork length).     

Variations in the sizes of gonads,eggs and larvae of the dace,Leuciscus leuciscus

Synopsis Prespawning female dace were examined in 7 successive years; in 6 years mean egg size (mm³) and egg number were inversely related and hence the ovary weights of equivalent-sized females were constant. Fecundity increased logarithmically with fish length, and an index of reproductive effort (ovary weight ÷ length cubed) also increased. The number of eggs per gram of ovarian tissue decreased with fish length; this was because mean egg size (mm³) increased and not because of a change in the proportion of connective tissue in the ovary. But in 1977, both egg number and mean egg size were low, although very high somatic growth had occurred in the previous, very warm, summer of 1976. Eggs from different-sized female dace were artificially fertilized, and incubated at a constant temperature. Dry weights of larvae, egg dry weights, mean egg size and larval starvation times showed linear correlations with each other and with parental (female) lengths. The progeny from the very smallest parent died several days earlier than those from the other parents. Size-related predation rates may be of more consequence than starvation death in natural populations. The optimum position of dace along the continuum between many small eggs and fewer larger eggs may vary at different levels of reproductive effort.     

The fecundity of dace, Leuciscus leuciscus (L.) in Emral Brook, Clwyd, North Wales

SUMMARY. Estimates of the fecundity of dace were made on 105 mature females using the dry method of Simpson (1959). The reliability of the counting procedure was assessed and found to be satisfactory. Fecundity was examined in relation to fork length (cm), somatic weight (g), ovary weight (g) and age (years). Logarithmic multiple regressions of fecundity on these variables showed that neither log fork length nor log somatic weight contributed significantly towards explaining the observed variations in fecundity. The best prediction equation for fecundity, incorporated both log ovary weight and log age. Incidents of extensive follicular atresia were found in the ovaries of 19% of the female dace examined and the frequency of occurrence of this phenomenon increased with age.     

The annual reproductive cycle of pike, Esox lucius L., in two Scottish lakes

Histological changes in the ovaries of pike from two shallow, adjacent, Scottish lakes are described and related to a macroscopic scale of maturity stages and to changes in gonad weight. There was no evidence of pre-ovulatory degeneration although occasional residual oocytes were present in spent ovaries. The gonadosomatic index (GSI) was high in males from October to March, and in females it increased through the winter months to a maximum immediately prior to spawning. Maximum ovarian weight was 8.3–9.0% of total body weight compared with only 0.9–1.1% for testes. These GSIs were low compared with other reports for the British Isles, suggesting lower reproductive output. Spawning occurred in the first two weeks of April at a water temperature of 6.0–7.5° C. Fecundity was described from a regression of egg number (F) on fork length (f.l.): log₁₀F= -1.51 + 3.33 log₁₀ f.l. (cm). Mean egg diameter after preservation varied from 1.1 to 2.4 mm over the size range examined. Males were mature at age 2 at a length of ≥ 27 cm, while females first spawned at age 3 at a length of ≤ 28 cm, although a minority were mature at age 2. The sex ratio was 1.2 males: 1 female at Kinord and 1.4 : 1 at Davan. Greater egg production at Davan, 50 678 ha^?1, compared with Kinord, 33 557 ha^?1, was due to higher individual fecundity-at-age resulting from better growth. Fecundity (19.29 × 10³ calculated for a pike of 55 cm F.L.), relative fecundity of only 10–24 eggs per gram wet weight of adult, and GSI values were low compared with pike in North America and Eurasia. Food supply may restrict reproductive output of pike in Lochs Kinord and Davan. The abundance ratio of predator: prey is high with the main prey species, perch, present in low numbers, and the only alternative species is eel in these simple fish communities.     

Reproductive biology of brown trout, Salmo trutta macrostigma Dumeril 1858, in a tributary of the Ceyhan River which flows into the eastern Mediterranean Sea

The study describes some key elements of the reproductive biology, including spawning season, age at sexual maturity, fecundity and egg diameter of the native brown trout, Salmo trutta macrostigma, in a tributary of the Ceyhan River. A total of 197 brown trout (118 females and 79 males) were captured in 2000–2001 by electric fishing. In observations on monthly changes, the gonadosomatic index (GSI) and the monthly frequency distribution of egg diameter confirmed that spawning lasted from November to January. Some 27.7% of the females and 62.5% of the males attained sexual maturity in their second year. The smallest fork length (FL) of brown trout attaining sexual maturity was 17.4 cm for males and 17.8 cm for females. Mean fecundity in age groups II, III, IV and V were 360, 452, 693 and 1283 eggs per female, respectively. One 9‐year‐old female had a unique 3232 egg count. The mean fecundity of the sampled population was 554 eggs per fish, positively correlated with the FL (mm) (R = 0.8227 ) and body weight (R = 0.8130). The diameter of mature eggs in the spawning season ranged from 3.250 to 5.930 mm, with a 4.146 mm average. Mean egg diameter in age groups II, III, IV and V in the spawning season were 0.813, 3.799, 4.663 and 5.243 mm, respectively. Fecundity, egg weight and diameter were statistically different in all age groups.     

The structure and dimensions of redds and egg pockets of the endangered salmonid, Sakhalin taimen

Each redd of the Sakhalin taimen Hucho perryi had a V–shaped pot that is specific to this species. The shape of each multiple–egg–pocket redd was a combination of one–egg–pocket redds, and the number of egg pockets in the redd could be estimated from the shape. False redds were small and did not have any V–shaped pots. The factors affecting redd size were examined numerically; consequently, numbers of egg pockets and eggs and female fork length were correlated significantly with tail length. Each egg pocket contained 11–920 eggs (mean: 546·7±95% CL 81·9) and the egg pocket depth was correlated significantly with female fork length. Mean number of redds per female was three, and the number of females could be estimated as one third of the redds.     

Reproduction in fish of the Weddell Sea

Reproductive characteristics of 28 fish species were obtained during EPOS leg 3 in the inner Weddell Sea The gonadosomatic index (GSI) of female notothenioid fish was 15–30% at spawning. GSI in males was much less. Length at first spawning was attained from c. 70% of the maximum total length onwards. As in species of the low-Antarctic Zone gonad maturation was obviously a biennial process. More species in the high-Antarctic Zone spawn in summer and winter than in the low-Antarctic Zone where spawning in autumn/winter prevails. Fecundity was positively correlated with fish length and weight among most species. Fecundity exceeds 10,000 eggs only in a few nototheniid species. Egg diameter is commonly 3.5–5.0 mm with icefish having the largest egg sizes. Eggs of most species are probably left unattended, but nest guarding was suspected in the less fecund species. The results are discussed in comparison to reproduction in notothenioid fish inhabiting the low-Antarctic Zone.     

Reproduction, diet and population structure of the mountain mullet, Agonostomus monticola, in Jamaica, West Indies

Reproduction, feeding and population structure were investigated in the mountain mullet, Agonostomus monticola, in eastern Jamaica between 1982 and 1986. Female fishes just outnumbered males 1.2 : 1. Minimum size at maturity for females was 123 mm fork length (FL) and 96 mm FL for males. Mean size at maturity for females was 165.8 mm FL (S.D.=1.61) and for males was 148.4 mm FL (S.D.=2.97). Fecundity was 340 000 eggs for a 25 g ovary. Fecundity (F) was related to size by the equation F=153.8 FL^1.36. Mean lengths of males and females captured by all methods were 129.4 mm (S.D.=5.56) and 160.4 mm FL (S.D.=0.70), respectively. A. monticola was found to be chiefly an insectivorous feeder. The major food items found in stomach contents in ranked sequence were insects, freshwater prawns, plant detritus and algae.     

Histological investigation on the ovarian cycle of the bluefin tuna in the western and central Mediterranean

The histological analysis of eastern Atlantic bluefin tuna Thunnus thynnus ovaries caught from February to September 1999–2000, made it possible to distinguish the presence of seven oocyte developmental stages and allowed the characterization of six time-dependent ovary maturity stages. The ovaries of mature (fork length, L _F ≥ 110 cm) bluefin tuna were non-active from August (spent period) to March (quiescent period) when they contained only perinucleolar-stage oocytes. Ovary development started in April to early May (recrudescent period) with the appearance of oocytes at the lipid stage. Vitellogenesis appeared in mid-May (ripening period) and post-vitellogenesis occurred in late May to mid-June (pre-spawning period). In late June to early July, hydrated oocytes, a sign of imminent spawning, were found only in specimens caught in Balearic waters. Females ranging between 100 and 110 cm L _F, captured during the recrudescent and ripening periods, had the largest oocytes at the lipid stage, most of which were degenerating. An extensive vitellogenic atresia was observed in the ovaries of five females caught during the spawning period in non-spawning areas.     

Some aspects of the reproductive biology of perch Perca fluviatilis L. Fecundity, maturation and spawning behaviour

Fecundity of perch estimated from a regression of egg. number on fish length varied from 6711 for a fish of 14.5 cm to 77978 for a female of 34. 5 cm. Other independent variables related to egg number were age, gonad weight and somatic weight. Mean egg diameter varied from 0.94 to 1.62 mm. Males matured in their second year at a length of 6 cm and above while all females spawned at age four at a length of 15–18 cm. A proportion of females at Davan spawned one year earlier than at Kinord and were also slightly smaller on spawning. Faster growth of Davan fish may have encouraged earlier maturation. Spawning behaviour is described from film material.     

Fecundity of the three-spined stickleback, Gasterosteus aculeatus (L.)

The number of eggs spawned by female three-spined sticklebacks Gasterosteus aculeatus (L.) was highly correlated with the size of the fish expressed either as total length or as weight after spawning. There were no significant correlations between the size of the eggs measured either as wet weight per egg or as dry weight per egg, and the size of the fish. Nor were there significant correlations between the calorific value of the eggs and the length or weight of the fish. Regressions relating egg production to the length and the weight of the fish are given. These results and an analysis of previous studies on the fecundity of the stickleback suggest that variations in fecundity are primarily a reflection of variation in the size of the fish at maturity, and that this size is related to the race of the stickleback and to environmental conditions such as food supply which influence the growth of sticklebacks.     

Reproductive biology of anadromous arctic char,Salvelinus alpinus (L.)? in the Cumberland Sound area of Baffin Island

The ovaries of anadromous arctic char, Salvelinus alpinus (L.), captured during 1973 from four high arctic rivers on Baffin Island started to increase in weight early in July and were at their heaviest in mid-September just before spawning. At this time, 40 cm (615 g) char from two rivers contained ovaries weighing 17.0 g (dry) which differed significantly from the 22.5 g gonads of comparable char from the other two areas. Gonadal development in male fish began in June and the diameter of testes at full maturity (3.0–4.0 cm) was similar regardless of river system. Fecundity of comparable fish varied significantly among the rivers with char 40 cm in length containing 1400–2400 eggs while the corresponding values for 60 cm (i.e. 2050 g) char ranged from 4000–5500. The diameter of both immature and mature eggs was similar regardless of system. Values for immature eggs averaged 0.64 mm in 40 cm fish and 1.60 mm in 60 cm specimens. Diameter of mature eggs, on the other hand, was considerably greater (3.2 and 4.3 mm, respectively). Maturity was first reached at age 10 (i.e. 35 cm) in both males and females and maturing fish of both sexes were not always restricted to fresh water. Redd construction occurred at a depth of one to at least 11 m at a temperature of 0.5–4.0° C. The percentage of eggs retained in the body cavity after spawning varied from 0.22–1.50 and the mortality rate of spawned eggs was extremely low.     

Fecundity and its variability in orange roughy: effects of population density, condition, egg size, and senescence

Fecundity of orange roughy in 1987–1989 adjusted for standard length (S.L.) varied significantly between New South Wales (42 787 eggs female⁻¹) South Australia (35 339 eggs female⁻¹) and east Tasmania (31 085 eggs female⁻¹). Only 10-17% of the variability in fecundity of eastern Tasmania orange roughy was explained by s.l . in any year from 1987–1992. However, liver condition and age of the fish, in combination with s.l ., explained 27% of the variation in fecundity. Fecundity declined in fish over 60 years old. It was also significantly correlated with lipid levels in the ovary, in particular, with triacylglycerol as a proportion of the total lipid fraction. Significant interannual changes in fecundity appeared to be related to the impact of fishing. From 1987–1992, the orange roughy stock off east Tasmania was reduced by 50% by the fishery, and mean fecundity increased 20% over that period. This compensatory increase in individual fecundity, combined with an apparent increase in the proportion of females spawning annually from 54 to 71%, limited the decline in the population's egg production over this period to approximately 15%.     

Reproductive biology of the East African lungfish (Protopterus aethiopicus) in Mwanza Gulf, Lake Victoria

The population of lungfish (Protopterus aethiopicus (Heckel)) was sampled by bottom trawling for 12 months from June 1984 to May 1985. A total of 576 lungfish were investigated. The sex ratio in the population was 1 male : 1 -98 females. Average size at maturity was found to be 960cm total length (TL) but the smallest matured male measured 72-9 cm and the female 840 cm TL. It was not possible to establish spawning times and reproductive activity trends either from the variation in relative condition factor ‘kn’ or from gonadosomatic index (GSI). Whereas male lungfish seem to show no further increase in GSI after gonadal maturity stage III, females exhibit GSI values that vary directly with oocyte maturation and ovarian weights. Fat deposited along the gonads was found to be a better basis for assessing maturation and spawning in lungfish. The potential spawning period was found to be from September to May. Absence of lungfish with spent gonads over the 12-month period and the presence of different egg sizes in ovaries, suggest that the fish is a multiple spawner. Fecundity was found to range from 705 eggs (in 84-cm TL fish) to 14,922 eggs (in 130-cm TL Fish).     

Length-dependent changes in egg size and fecundity in females, and brooded embryo size in males, of fork-tailed catfishes (Pisces: Ariidae) from the Sepik River, Papua New Guinea, with some implications for stock assessments

Data suggest that mature egg weight is positively correlated to female parent length in all five species of fork-tailed catfish studied. Embryo weight is positively correlated with the length of the male mouthbrooding parent in the four species where data are available. Non-random mate pairing is probably between fish of equivalent size. Fecundity appears to be linearly related to female fish length in all species. There is no significant correlation between fecundity and female weight, probably because egg size increases with fish size. Low fecundities and breeding behaviour suggest that recruitment is likely to be highly density-dependent and the stocks vulnerable to increased mortality (fishing). Changes in egg size with fish size may account for deviations from a cube relationship between fecundity and fish length in other species. The relevance of this to other fish stock assessments is discussed. Attention is drawn to possible changes in egg size with fish length which could affect recruitment in fished stocks, depending on the specific relationship and the length at which mature fish are caught.     

Egg Load and Body Size of Lab-cultured Cotesia marginiventris

The egg load of lab-cultured Cotesia marginiventris (Cresson) (Hymenoptera: Braconidae), a solitary koinobiont endoparasitoid of noctuid caterpillars, was determined in this study. Information on egg load may provide clues to more efficient in vivo rearing of C. marginiventris. I tested the hypothesis that egg load, defined as the number of mature oöcytes (i.e., fully chorionated eggs) found in adult females, was related to body size. Cotesia marginiventris females possessed two ovaries and two ovarioles per ovary; mature eggs were found in ovaries and oviducts. Newly-emerged females held an average of 149 mature eggs. Immature eggs were slightly visible in the distal portions of the ovarioles; they were not counted. Egg load was marginally related to body size (i.e., hind tibia length). The results of this study suggest that (1) body size can sometimes predict egg load or potential fecundity of lab-cultured C. marginiventris and (2) an efficient rearing system that exploits the potential fecundity of C. marginiventris might involve using young females and allowing them to oviposit in new hosts, each day, for up to a week.     

The age, growth and reproduction of the stone loach Noemacheilus barbatulus (L.) in a Dorset chalk stream

SUMMARY.

• 1 In this highly productive chalk stream the stone loach, sampled by electrofishing over a 30 month period, had a high growth rate reaching a mean length of 65 mm in 1 year and 93 mm in 2 years. The fish were short-lived in contrast to most slow-growing populations in the U.K. and Finland with 11 group fish comprising 8.8% and III group fish only 1.1% of the total number.
• 2 The loach were fractional spawners: a 75 mm female produced an estimated 10,620 eggs between late April and early August totalling 46% of the loach's initial weight.
• 3 In March and April some small 0 group females contained only poorly developed eggs and up to 10% of 0 group fish may have failed to spawn.
• 4 Amongst loach >52 mm in length in March and April there was an exponential relationship between absolute fecundity and fish length but no relationship between relative fecundity and length. There was. however, a relationship between fish length and both gonadosomatic index and maximum egg size, which may indicate that large fish began to spawn first.

     

Assessment of egg quality and realised fecundity of whiting Merlangius merlangus L. in captivity

Potential predictors of egg quality were assessed in whiting Merlangius merlangus L. permitted to spawn in a tank from which eggs were collected. These included fertilisation rate, the proportion of viable buoyant eggs, egg diameter, and egg wet and dry weights; all were influenced by temporal effects and were negatively correlated with days from start of spawning. The spawning period was protracted, from February to June. Mean daily egg production per female was 2.74 ± 2.43 g and 2338 ± 2075 eggs, equivalent to 14.6 ± 13.1 g kg^?1 day^?1 female^?1. Egg diameter was 1.21 ± 0.04 mm, egg wet weight 1.20 ± 0.21 mg, dry weight 0.10 ± 0.02 mg, and mean fertilisation rate and hatching rates were 76.8 and 73.3%, respectively. The incubation period ranged from 72 to 80 degree days and was dependent on temperature (x) and described by the equation y = 25.92 e^?0.1219x. Realised fecundity was also assessed to determine if this gave a more accurate measure of reproductive potential, and this was compared with potential fecundity estimated from predictive regressions on fish length from fisheries data. Realised egg production of 20 females of 185 g mean weight and 256 mm fork length was 4 444 360 (95% CL 4 093 961–4 743 018), similar to predicted seasonal egg production based on gravimetric fecundity measurements of wild caught fish.     

Prey resources before spawning influence gonadal investment of female, but not male, white crappie

In this study, an outdoor pool experiment was used to evaluate the effect of prey resources during 4 months before spawning on the gonadal investments of male and female white crappie Pomoxis annularis , a popular freshwater sportfish that exhibits erratic recruitment. Fish were assigned one of three feeding treatments: starved, fed once every 5 days (intermediate) or fed daily (high). All measurements of male testes ( i.e. wet mass, energy density and spermatocrit) were similar across treatments. Conversely, high-fed females produced larger ovaries than those of intermediate-fed and starved fish, and invested more energy in their ovaries than starved fish. Compared to pre-experiment fish, starved and intermediate-fed females appeared to increase their ovary size by relying on liver energy stores ('capital' spawning). Conversely, high-fed females increased liver and gonad mass, implying an 'income'-spawning strategy (where gonads are built from recently acquired energy). Fecundity did not differ among treatments, but high-fed fish built larger eggs than those starved. Females rarely 'skipped' spawning opportunities when prey resources were low, as only 8% of starved females and 8% of intermediate-fed females lacked vitellogenic eggs. These results suggest that limited prey resources during the months before spawning can limit ovary production, which, in turn, can limit reproductive success of white crappies.     

Sperm storage and motility in the ovary of the marine sculpin Alcichthys alcicornis (Teleostei: Scorpaeniformes), with internal gametic association.

Elkhorn sculpin, Alcichthys alcicornis, is a marine teleost with a unique reproductive mode called "internal gametic association," in which sperm introduced into the ovary by copulation enter the micropylar canal of ovulated eggs in the ovarian cavity, but actual sperm-egg fusion does not occur until the eggs have been released into sea water. It is also known that this fish is a multiple spawner, which spawns at intervals of a few days for one month, and the sperm introduced into the ovary at the beginning of the spawning season retain their fertilizability for the entire period. To clarify how the fertilizability of sperm is maintained internally, the ultrastructure of sperm, the morphological characteristics related to sperm storage in the ovary, and the characteristics of sperm motility were investigated. Mature sperm generally have the normal form of teleost sperm, devoid of acrosomal structures. However, it was found that the midpiece is comparatively elongated and has a compact aggregation of many small-size mitochondria. The intraovarian sperm remained floating in the ovarian fluid throughout the spawning season. The sperm showed high motility in isotonic and weak alkaline solution, containing sodium ions, which was similar to the ovarian fluid of this fish. Sperm continued to move in artificial ovarian fluid for 7-14 days. Considering these results together, it is thought that the intraovarian sperm move throughout the spawning season due to the plentiful energy generated by the many mitochondria.