The relationship between fecundity and fertility in the mouthbrooding cichlid fish Tilapia leucosticta

The development of fry in the mouth of the female mouthbrooder Tilapia leucosticta Trewavas is described. The egg production by fish of various lengths is plotted and a curvilinear regression for standard and total length fitted. The number of eggs produced is approximately equal to the square of the total length in centimetres of the parent fish. The brood numbers of 460 females are plotted against length, and linear regressions for mean brood number and mean fry number fitted. The relationship between the expressions for numbers of fry brooded and egg production gives an estimate of brooding efficiency that decreases with increasing parent length. Individual female fish show signs of reripening and the timing of this process is estimated from gonad state and from the length of fry brooded in the mouth. The relationship between fecundity (egg production) and fertility (fry brooded) is considered and the effect of maturation size, growth rate and spawning frequency assessed.     

Factors affecting mate desertion by males in free-ranging convict cichlids (Cichlasoma nigrofasciatum)

Convict cichlid fish have biparental care for a period of about6 weeks lasting from egg laying until the young (fry) have grownto about 10 mm. However, the young can sometimes survive withcare from only one parent, and desertion of the mate and offspringby males has been observed. I tested a theoretical model modifiedfrom Lazarus (1990) which predicted that mate and offspringdesertion by male convict cichlids should be promoted by lowpredation pressure on fry, high remating opportunities for males,increasing age of fry, and decreasing number of fry. Males deserted7.8% of 334 broods studied during two breeding seasons in CostaRican streams. As predicted, males deserted their broods mostfrequently at sites with the highest brood survivorship (lowestbrood predation pressure), when fry were close to independenceand when brood size was smaller than average. Sex ratios andinterspawning intervals did not indicate any relationship betweenmate desertion and opportunities for remating for males. Thereuse of spawning caves may favor fidelity to the mate and brood,and defending the young from predators at the same time as defendingthe cave from conspecifics may favor biparental care in thisspecies.     

Treatment with thiamine hydrochloride and astaxanthine for the prevention of yolk-sac mortality in Baltic salmon fry (M74 syndrome).

Two practical methods are reported for treating feral Baltic salmon with thiamine hydrochloride against M74 syndrome (abnormally high yolk-sac fry mortality of the Baltic salmon). Both bathing of the yolk-sac fry in thiamine hydrochloride (1000 mg l-1, 1 h) and a single intraperitoneal injection given to the female brood fish (100 mg kg-1 fish) during the summer 3 mo before stripping were shown to elevate the whole body total thiamine concentration in the fry. Both treatments were also shown to be effective in preventing mortality due to M74 syndrome. The effect of bathing the yolk-sac fry was shown to be dose-dependent. The results support the view that there is a causal relationship between the thiamine status of the yolk-sac fry and M74 mortality. An intraperitoneal injection of astaxanthine suspension administered to the female brood fish (11 mg kg-1 fish) in the summer 3 mo before stripping elevated the astaxanthine concentration in the eggs but did not affect mortality due to M74 syndrome. An interaction between astaxanthine and thiamine may occur in the developing embryo or yolk-sac fry, however. No association could be demonstrated between the various thiamine hydrochloride treatment practices and hepatic cytochrome P450 dependent 7-ethoxyresorufin-O-deethylase (EROD) activity in the yolk-sac fry. An injection of thiamine hydrochloride into the peritoneal cavity of wild Baltic salmon females could be used to raise thiamine concentrations in their offspring in the rivers. The effect on smolt production in Finnish Baltic salmon rivers needs to be investigated further, however.     

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.     

Brooding in Psolus patagonicus (Echinodermata: Holothuroidea) from Argentina, SW Atlantic Ocean

The mode, season, and time of brooding, egg diameter, egg number per brood, and the characteristics of newly released juveniles of Psolus patagonicus were investigated off Mar del Plata, Buenos Aires, Argentina, between October 1999 and February 2001. Individuals were attached to the Patagonian scallop, Zygochlamys patagonica. Spawning occurs between February and March. The mean egg diameter, 887 ± 26 μm, is the highest reported for the family Psolidae. Eggs are brooded under the mother’s sole until they develop into crawling juveniles within 7 months. The largest embryos reached a length of 1,941 ± 228 μm in September. During the brooding period (February–September) the number of brooded embryos decreased while their size increased. Our study confirms brooding behaviour in female P. patagonicus.     

THE GENETIC BASIS OF LIFE-HISTORY CHARACTERS IN A POLYCHAETE EXHIBITING PLANKTOTROPHY AND LECITHOTROPHY

The polychaete Streblospio benedicti is unusual in that several field populations consist of individuals that exhibit either planktotrophic or lecithotrophic larval development. Planktotrophy in this species involves production of many small ova that develop into feeding larvae with a two- to three-week planktonic period. Lecithotrophy involves production of fewer, larger ova that develop into nonfeeding larvae that are brooded longer and have a brief planktonic stage. Reciprocal matings were performed to investigate genetic variance components and the correlation structure of life-history traits associated with planktotrophy and lecithotrophy. Our objective was to better understand persistence of this developmental dichotomy in Streblospio benedicti, and among marine invertebrates in general. Substantial additive genetic variation (75–98% of total) was detected for the following characters at first reproduction: female length; position of the first gametogenic setiger and first brood pouch; ovum diameter; three traits related to fecundity (numbers of ova per ovary, larvae per brood pouch, and larvae per brood); median larval planktonic period and the presence of larval swimming setae; but not for total number of brood pouches; larval length; larval feeding; and larval survivorship. Based on the unusual geographic distribution of development modes in this species, we hypothesize that the developmental traits have evolved in allopatry and have only recently come into contact in North Carolina. The high additive contribution to variance observed for many traits may be inflated due to (a) nonrandom breeding in nature, and (b) examination of only one component of an age-structured population at one time. Nuclear interaction variance and maternal variance accounted for 84% of the total variation in larval survivorship. This observation supports other empirical studies and theoretical predictions that nonadditive components of variance will increase in importance in individual traits that are most closely tied to fitness. A network of life-history trait correlations was observed that defines distinct planktotrophic and lecithotrophic trait complexes. Negative genetic correlations were present between fecundity and egg size, between fecundity and position of the first gametes, and between larval survivorship and median planktonic period. Positive genetic correlations were detected between fecundity and female size at first reproduction and between planktonic period and the presence of swimming setae. Intergenerational product-moment correlations were negative for larval length and fecundity, planktonic period and egg size, female size and larval survivorship, and fecundity and larval survivorship. If the genetic correlation structure observed in the laboratory persists in the field, it may constrain responses of individual characters to directional selection, and indirectly perpetuate the dichotomies associated with planktotrophy and lecithotrophy.     

Shifting body weight-fecundity relationship in a capital breeder: maternal effects on egg numbers of the autumnal moth under field conditions

In the literature, various environmental factors are described as being capable of influencing the reproductive output of insect females irrespective of their body size. Still, female body size or weight is widely used as a proxy for fecundity. In the present study, a seven-year data set on the autumnal moth, Epirrita autumnata (Borkhausen) (Lepidoptera: Geometridae), was used to analyze whether the body weight-fecundity relationship in this capital breeding, cyclic forest defoliating lepidopteran is constant across years. Ambient temperature conditions and density of conspecifics during larval development, the length of the pupal period, as well as moth densities in the parent generation were examined as factors capable of modifying the body weight-fecundity relationship. While the regression slope of potential fecundity (total egg numbers per female) on pupal mass was constant across years, the mean total egg number per given body weight (the regression intercept) was significantly different between years. This residual variance in egg numbers after controlling for the effect of pupal mass was best explained by the pooled geometrid density (autumnal and winter moths) in the parent generation. The total egg number per given body weight decreased with increasing density of geometrid moths in the parent generation. Thus, maternal density effects on offspring fecundity were found in this system. Their rather weak nature suggests, however, that this maternal effect alone does not have the potential of causing cyclic population dynamics in the autumnal moth.     

High brood patch temperature of less colourful,less pheomelanic female Barn Swallows Hirundo rustica

In birds, even a minor difference in egg temperature (1–1.5 °C) has been shown to affect the fitness of offspring by changing hatching success, incubation period and nestling quality. Female, but not male, passerines develop brood patches. Thus if there are traits, such as plumage ornamentation, that indicate optimal egg temperature, males should pair with females that exhibit those traits. However, no study has yet investigated the relationship between female brood patch temperature, which would directly affect egg temperature, and female plumage ornamentation. In this study, we examined the surface temperature of female brood patches during nocturnal incubation and examined its relationship with female plumage ornaments in Asian Barn Swallows Hirundo rustica gutturalis. After controlling for ambient air temperature, brood patch temperature was negatively associated with colour saturation of the female throat patch. No other female ornaments, such as tail‐length, white tail spots or throat patch size, predicted brood patch temperature. When oral (mouth) temperature was statistically controlled, females with less colourful throats and longer tails showed higher brood patch temperature, indicating that these females had hotter brood patches in relation to the temperature of other body parts. Furthermore, we found a negative relationship between pheomelanin pigmentation and brood patch temperature after controlling for ambient air temperature or oral temperature. To our knowledge, this is the first study to show that female ornaments can predict the absolute/relative thermal investment in brood patches. This relationship, together with other aspects of female quality, may affect male mate preference and female ornamentation.     

The reproductive success of pike, Esox lucius: aspects of fecundity, egg density and survival

Power-law relationships have been estimated between fecundity and fish length, weight and age for pike from two gravel pit lakes (Main Lake and St Peter's Lake) in Buckinghamshire, England. Relative fecundity, estimated at 17.6 eggs g⁻¹ for Main Lake pike and 19.4 g⁻¹ for St Peter's Lake pike, did not differ significantly between the lakes. Population fecundity for the Main Lake was estimated at 10.6 million eggs and 6.4 million eggs in 1986 and 1987, respectively.
Experimental work involving samples of eggs from 18 artificially fertilized Main Lake female pike showed a significant relationship between egg diameter and female length, and a significant difference between mean egg diameters for 41-cm and 101-cm females. No significant relationships were found between mean egg size and mean fry size, nor between fry length and adult length. Mean size differences between newly hatched, 18-day-old and 41-day-old fry from the 41-cm and 101-cm females were not significant.
Samples of eggs taken at 2-day intervals from 6 April to 5 May in a pike spawning area of the Main Lake revealed clumped distributions of eggs, with average egg densities ranging from 1 to 47 eggs per 0.071 m² (14–671 m ²) on sand and silt substrata. The maximum egg density of 51 per 0.071 m² (729 m⁻²) was found on flooded grass. The stages of development of the eggs were identified over the sampling period. Survival from stage 1 to fry was estimated at 3–6%. Egg losses were estimated at 9–10% day⁻¹.
Egg survival experiments gave overall hatching success rates of 11 % on sand/silt compared with 2.5% on aquatic plants (1986), and 18.9% on undisturbed sand/silt compared with 7.9% on disturbed sand/silt (1987). The effect of siltation on egg hatching is discussed.     

Predicting fluctuations in the size of newly emerged sea-trout fry in a Lake District stream

The objective was to predict interannual fluctuations in the size of sea-trout fry when they emerged from the redd, using models developed from field data for 70 excavated redds (≥three per year), and from experimental data on egg and alevin development at 30 constant temperatures in the laboratory (range 1·5—10·5) C with 100 naturally fertilized eggs at each temperature). Egg weight increased with female length and also with the number of eggs laid in a redd, both relationships being well described by a power function. Early spawners were the largest females laying the largest and most numerous eggs, whilst late spawners were the smallest females laying the smallest and least numerous eggs, with middle spawners being intermediate between these two extremes. Mean values for egg weight and number of eggs per redd were obtained for these three groups. The numbers of early, middle and late spawners for each year of a 30-year study and the mean values from the excavated redds were used to estimate weighted means for the number of eggs per unit area and egg weight. Mean values varied considerably between years (30-year ranges: 518–7964 eggs per 60 m2; 112–138 mg wet weight). In the laboratory, mean weights of newly hatched alevins and newly emerged fry were both related positively to mean egg weights. Alevin and fry mean weights were independent of the number of days required for 50% of the eggs to hatch or fry to emerge. Models described in a previous paper formed the basis of those used to predict fry weights over the emergence period. Model predictions were validated by field data for the whole emergence period in 8 years (1967–1971, 1974, 1975, 1980), and by pre-fry weights on single dates in 21 years (1967–1987). As pre-fry densities on these single dates were very similar to egg densities for the same year class, mortality in the egg and alevin stages was very low. The chief objective was therefore fulfilled, and the extent of interannual fluctuations for the 30-year study showed some variation in mean fry weight (30-year ranges: 153–193 mg for both the whole emergence period and the date on which 50% of fry emerged) but a progressive decrease in fry weight through the emergence period. Possible reasons for this variation are discussed, and it is concluded that the size of the female spawners is the dominant factor.     

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.     

Structural study of the ovary,oogenesis and brooding in Tonicia lebruni (Polyplacophora Chitonidae) from Patagonia

Tonicia lebruni, a common, lower intertidal and subtidal chiton inhabiting Patagonian rocky shores, is a gonochoristic iteroparous species producing large eggs (≈ 400 μm in diameter), which are fertilized and brooded within the pallial groves until released as juveniles. A free larval stage is absent, despite this, T. lebruni is widely distributed along the south‐western Atlantic. At Puerto Deseado, T. lebruni has a marked seasonality in the reproductive cycle, reproducing only once a year. The reproductive period is quite short and defined in time: spawning and brooding take place during the late austral winter and beginning of spring. Recovery of the female gonad starts very soon after spawning. Oogenesis takes about 10–11 months for completion. Brood size is correlated with length of maternal individual. The number of embryos per brood varied between 785 and 5945. Extensive resorption of abortive eggs is viewed as related to limitation of space available for brooding. The egg hull is formed by a large number of minute pentagonal or hexagonal plates each one bearing a short spine bent onto the egg surface. The morphology and the surface of the hull could contribute to the cohesiveness of the brooded egg mass within the pallial grooves.     

The benefits of uniparental versus biparental mouth brooding in Galilee St. Peter's fish

In Galilee St. Peter's fish Sarotherodon galilaeus the care system is naturally labile; biparental, male-only and female-only care all exist in one population. This unusual flexibility facilitates comparisons between the forms of care. The costs of parental care were considered in a previous study. Here, the benefits of parental care were quantified by observing wild fish, both held in pond enclosures and free-swimming in Lake Kinneret, Israel. Parental care was shown to be essential for offspring survival in St. Peter's fish. The reproductive success of parents who shared incubation duties was nearly twice as high as that of parents caring alone. However, per brood (or mouth cavity) reproductive success was 20% higher for uniparental parents. Both sexes were equally capable and efficient in care; when both sexes cared, they each incubated a similar number of eggs and released a similar number of fry. The results are discussed in terms of the relationship between caring Strategies and clutch size.     

食蚊鱼生殖特性的研究

食蚊鱼Gambusia affinis(Baird et Girard)属于鱂形目(Cyprinodontiformes)、胎鱂科(Poeciliidae)。是一种原产北美洲的热带性卵胎生小鱼。这种鱼自1927年从马尼拉引入我国后,已成为遍及我国南方淡水小鱼,并在灭蚊控疟方面发挥一定作用。有关其繁殖生物学Rosen,D.E.et al.（1963）,Resenthal,H.L.（1952）,Turner,C.L.（1937,1941.）曾有过报道,为了补充食蚊鱼繁殖生物学资料,作者在1979—1982年在广州对其生殖特性作了观察研究。     

Experimental study on population dynamics in the guppy, Poeclia reticulata (Peters). Effect of shelters on the increase of population density

To study mass culture of the guppy, Poecilia reticulata (Peters) for use in mosquito control, the population dynamics of the fish were studied in 10001 polycarbonate tanks with and without shelters for fry, under conditions of constant temperature and filtration of water, and sufficient food supply. In the tank with shelters, the maximum density attained was 5.84 fish per 1 at the 77th week, when the initial population had been 25 males and 25 females. After this period the density began to decrease and dropped to 1.04 fish per 1 at the 105th week. Conversely, in the tank without shelters, almost no increase in number took place when the population started with either 50 adult fish or 25 fry. The sex ratio of the guppies in the 10001 tank with shelters varied. In particular, females increased in. relation to male when the fry which had been produced in large quantities became sexually mature. The intervals between spawning averaged 38 days with a range of 26 to 90 days. An equation, log Y =0.0443X-0.2968 expresses the relationship between the number of young in the brood and the body length of the females.     

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.     

Parental care trade‐offs in the inter‐brood phase in Barn Swallows Hirundo rustica

In seasonal environments with limited time and energy resources, double‐brooded birds face trade‐offs in the timing of their two reproductive attempts and in the effort allocated to the first and the second broods. In the Barn Swallow Hirundo rustica a long care period for the first brood enhances the survival of first‐brood chicks, but also delays the start of the second brood, which in turn reduces the survival prospects of second‐brood chicks. Probably as a response to this trade‐off, double‐brooded Barn Swallows reduce the period of post‐fledging care for first‐brood fledglings. By radiotracking whole families, we investigated the determinants of this behaviour and its consequences for the survival of the first‐brood fledglings. The end of the females’ investment in post‐fledging care of the first brood was related to the beginning of egg synthesis for the second clutch. With the start of egg synthesis, females significantly reduced provisioning rates to the first‐brood fledglings to less than one‐fifth of the previous rates, while the proportion of time they spent foraging remained high. Assuming that the females’ foraging success was constant, we conclude that their energy income was allocated to egg production rather than fledgling provision. Males did not compensate for the females’ reduced feeding rates. Thus the start of egg production for the second clutch had a marked effect on the quantity of food received by first‐brood fledglings. In parallel with the changes in parental behaviour and provisioning rates, we observed a marked drop in the daily survival rate of first‐brood chicks. These results support the hypothesis that females face a strong trade‐off in the allocation of energy to subsequent broods. Energy allocation to a second clutch involves a cost in terms of reduced provisioning, and as a result the survival of first‐brood chicks is compromised. This is probably outweighed by the improved success of an early second brood.     

Population dynamics of Oreochromis shiranus in two small water bodies in Malaêi

Growth curves of Oreochromis shiranus in two small reservoirs, Chisombezi (2·2 ha) and Mbvoniha (3·6 ha), were constructed by fitting a seasonally oscillating von Bertalanffy growth function to tag-recapture data. Annual average numbers were calculated for each length class from gillnet cpue data corrected for selectivity. The lengths at first maturity were estimated from samples, and annual brood numbers were deduced from the linear relation between female length and brood number. Annual instantaneous mortality rates were estimated by linearized length-converted catch curves for lengths >90 mm, and for lengths between 10 and 90 mm by inference from the theoretical annual brood numbers. Estimated mean biomass was 84 and 106 kg ha ⁻¹, while production was 417 and 872 kg ha ⁻¹ year ⁻¹ in Chisombezi and Mbvoniha, respectively. Thus, the production-biomass ratios were high at 5.0 in Chisombezi and 8.2 in Mbvoniha.     

A numerical integration method for fish population fecundity

The numbers of eggs laid by an age group of fishes is underestimated by a simple multiplication of fecundity at the mean length by the numbers of females when the conventional logarithmic relationship between fish length and egg numbers is employed. This paper sets out the conditions under which the error becomes significant and derives a method of calculating the correct integral.     

An individual-based model for predicting the emergence period of sea trout fry in a Lake District stream

The objective of this study was to predict interannual fluctuations in the emergence period of sea trout fry, using models developed from field data for 70 excavated redds, and laboratory data on egg and alevin development at 30 constant temperatures (range 1·5–10·5° C with 100 naturally fertilized eggs at each temperature). Egg weight and numbers per redd both increased with female length; a power function described the relationship. Early spawners were the largest females laying the largest and most numerous eggs, whilst late spawners were the smallest females laying the smallest and least numerous eggs; middle spawners being intermediate between these two extremes. Mean values for egg weight and numbers of eggs per redd were obtained for these three groups. Hatching and emergence times in the laboratory decreased with increasing temperature. Of five models tested for hatching time, the best fit was provided by a three-parameter hyperbolic model which formed the asis of the individual-based model used to predict egg hatching and fry emergence. Model development was described in detail and the final equations predicted the times taken for 5, 50 and 95% of the fry to emerge, and hence the period over which 90% of the fry emerged. Analogous models were obtained for egg hatching. All models were excellent fits to the laboratory data. Hatching times for eggs kept in perforated boxes in the stream were almost identical to those kept at similar mean temperatures in the laboratory. Model predictions of fry emergence times were validated by field data for 8 years (1967–1971, 1974, 1975, 1980). The chief objective was therefore fulfilled, and predictions for the 30-year study (1967–1996) revealed a large variation in the timing of emergence (extremes: 11 March–4 April 1989, 15–20 May 1979). Most of the variation in median emergence date was due to variations in water temperature, with spawning dates as a secondary factor; the latter, however, had a greater effect on the length of the emergence period.