Effects of varying temperature and food availability on growth and reproduction in first‐time spawning female Atlantic cod

The somatic growth, sexual maturation and fecundity of individually marked first‐time spawning female Atlantic cod Gadus morhua were examined under different varying temperature and feeding regimes over the months preceding spawning. A negative correlation between somatic and oocyte growth was found, reflecting the changing energy allocation pattern. Nevertheless, the somatic growth of mature individuals was at least as high as those of immature fish over the period of vitellogenesis. Potential fecundity was positively correlated with body size, but neither temperature or feeding regime significantly affected this relationship. Consequently, fish with unlimited feeding opportunity invested more energy into somatic growth during vitellogenesis compared to those held under a restricted ration. This indicated that once Atlantic cod had made the decision to invest in first reproduction, they allocated a certain amount of energy relative to their size into egg production and any surplus was invested into somatic growth. Low temperature led to an arrest in the onset of vitellogenesis and significantly affected the number of females that matured.     

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.     

Biphasic growth in fish II: empirical assessment

In [Quince, et al., 2008. Biphasic growth in fish I: Theoretical foundations. J. Theor. Biol., doi:10.1016/j.jtbi.2008.05.029], we developed a set of biphasic somatic growth models, where maturation is accompanied by a deceleration of growth due to allocation of energy to reproduction. Here, we use growth data from both hatchery-raised and wild populations of a large freshwater fish (lake trout, Salvelinus namaycush) to test these models. We show that a generic biphasic model provides a better fit to these data than the von Bertalanffy model. We show that the observed deceleration of somatic growth in females varies directly with gonad weight at spawning, with observed egg volumes roughly 50% of the egg volumes predicted under the unrealistic assumption of perfectly efficient energy transfer from somatic lipids to egg lipids. We develop a Bayesian procedure to jointly fit a biphasic model to observed growth and maturity data. We show that two variants of the generic biphasic model, both of which assume that annual allocation to reproduction is adjusted to maximise lifetime reproductive output, provide complementary fits to wild population data: maturation time and early adult growth are best described by a model with no constraints on annual reproductive investment, while the growth of older fish is best described by a model that is constrained so that the ratio of gonad size to somatic weight (g) is fixed. This behaviour is consistent with the additional observation that g increases with size and age among younger, smaller breeding females but reaches a plateau among older, larger females. We then fit both of these optimal models to growth and maturation data from nineteen wild populations to generate population-specific estimates of ‘adapted mortality’ rate: the adult mortality consistent with observed growth and maturation schedules, given that both schedules are adapted to maximise lifetime reproductive output. We show that these estimates are strongly correlated with independent estimates of the adult mortality experienced by these populations.     

Reproductive biology, length-weight relationship and relative condition of pond raised Tilapia zilli (Gervais)

In 'runted' populations of Tilapia zilli positive correlations were found between maturation stages and the following: gonadosomatic index, gonad weight, fish weight and fish length. The minimum size at maturity was 9·0 cm in males and 11·0 cm in females. The mean fecundity in the 'stunted' females was 2359 eggs and it increased with length ( L ) weight (HO and depth ( D ) of the fish. There was, however, no correlation between fecundity and egg size. The results indicated that growth in this 'stunted' T. zilli population was not isometric. The relative condition factor ( Kn ) which approached one indicates good condition.     

Growth, maturation and reproductive investment in Arctic charr

Size and rates of growth in a cohort of 1 + Arctic charr housed in standard conditions were tracked over 12 months (December to December) and mature and immature males and females compared retrospectively. In both sexes, maturing fish were larger than non-maturing ones. In males, this size differential was the result of differences in growth in winter and early spring, but not in the remainder of the study period. In females, size differentials resulted mainly from growth rate differences immediately prior to breeding. In females but not in males, gonadosomatic index was predicted by growth rates in the months leading up to maturation, and among the females that matured, faster growing fish produced more eggs. Lipid reserves in July were correlated negatively with growth during the previous 7 months and, in females only, lipid reserves were significantly lower in maturing fish than in non-maturing fish, indicating that mobilization of lipid energy reserves in maturing fish had commenced by this time. Variation in investment in gonadal tissue, measured as gonadosomatic index, was not explained by variation in July lipid reserves for either males or females. However, July lipid reserves were negatively correlated with egg number, so females investing more in ova exhibited greater depletion of lipid reserves. These results are discussed in the context of the relationship between body condition and the onset of maturation in salmonids, relative investment in reproduction and sexual differences in the cost of reproduction.     

Social group size, potential sperm competition and reproductive investment in a hermaphroditic leech, Helobdella papillornata (Euhirudinea: Glossiphoniidae)

Social group size may affect the potential for sperm competition, and this in turn may favour ontogenetic adjustments in testicular mass according to the likely requirements for sperm and spermatophore production. In a number of comparative analyses of testis mass among vertebrate species that differ in mating system or social organization, increasing potential for sperm competition is associated with larger testis size. Intraspecific phenotypic plasticity should be able to produce the same pattern if social group size is heterogenous and reflects differing degrees of average sperm competition, but this intraspecific effect is less well studied. We tested the effect of social groups on both male and female investment in the simultaneously hermaphroditic leech, Helobdella papillornata. Leeches were placed in groups of one, two, four or eight. Sexual investment at the onset of reproductive maturity was quantified as the total testisac volume for male function and total egg volume for female function. We found that testisac volume (statistically adjusted for body size) showed a significant increase with increasing group size. Total egg volume (also adjusted for body size) was unaffected by group size. Our findings indicate adaptive developmental plasticity in male gonad investment in response to the potential for sperm competition.     

The reproductive cycle, condition and feeding in Barbus liberiensis, a tropical stream-dwelling cyprinid

This investigation examines the biology of Barbus liberiensis , a small cyprinid living in the forest streams of Sierra Leone and Liberia, in relation to seasonal changes in the environment. The population studied showed a single discrete breeding season coinciding with the early part of the rains. Maturing fish previously marked moved upstream at this time. The pattern of gonad development is analysed and the relationship of fecundity to body size is defined numerically. The total and somatic (i.e. excluding gonad weights) condition of the fishes, relative to the length/weight data in September-November when the gonads are resting, reach a peak at spawning time for both mature males and females and for immature fish. The pattern of condition during a year differs in the two sexes.
B. liberiensis consumes a wide variety of foods but relies largely on insects and higher plant fragments. Debris from the forest canopy is an important source of nutriment. The fish feed, during the daytime and possibly at night, throughout the year. Experiments to determine the rate at which food passes through the gut are described and show that food passage is rapid.
The seasonal cycles in condition and reproduction are discussed in relation to cycles in some other tropical and temperate riverine fishes.     

Body size versus gonad maturation form in under-yearling precocious males of the sea trout (Salmo trutta m. trutta L.)

The study was aimed at analysing body size in relation to form of gonad maturation (amount of mature germ cells) in 329 under-yearling sea trout males. The fish, aged 7 months, were caught in late October-early November in 3 streams located in north-western Poland. Each stream supported fish belonging to a different sib group. Standard histological techniques and a computer image analysis programme were used to detect the class of gonad maturation and percentage of the gonad area occupied by tubules with active spermatogenesis. Gonad maturation forms were distinguished based on the latter criteria. Gonads with developing germ cells occupying less than 90% of gonad area were classified as incomplete forms of gonad maturation, others as complete maturation forms. In each sib-groups analysed, even the smallest individual were already precocious, their gonads being incompletely mature. The smallest maturing male measured 7.1 cm in length. The average size of an incompletely maturing individual was slightly smaller than that of the completely mature one but the difference lacked statistical significance (P > 0.05). The sib-group of smaller fish contained less precocious, and the gonads of the more precocious were incompletely mature, compared to the sib-group of larger fish (P < 0.001). It seems that the incomplete form of gonad maturation (defected maturation) occurs at a smaller critical fish size than the complete gonad maturation form. Incomplete maturation is more frequent smaller individuals and possibly in among slow-growing groups of fish.     

Oocyte growth and development in teleosts

Oocyte growth and development is an important issue in fish and fisheries biology. This paper reviews the information available on oocyte growth patterns and the rates and dynamics of oocyte growth in teleosts. In synchronous spawners, the weight of the gonad may represent as much as 40% of the overall body weight of the fish. In asynchronous spawners, the weight of the mature ovary is considerably less than in synchronous ovulators, but the ovary shows a more regular periodicity and may grow repeatedly many times during the breeding season. There is a huge variability in egg size in teleosts, with the largest known measuring up to 8 cm in diameter. Within the limits of variance set by genetic constraints, egg size may vary between populations of the same species. Oocytes in all teleosts undergo the same basic pattern of growth: oogenesis, primary oocyte growth, cortical alveolus stage, vitellogenesis, maturation and ovulation. The mechanisms that control oocyte growth are addressed in this review, albeit that the available information, as in all other vertebrates, is very limited. The main hormones that have been shown to affect ovarian growth are gonadotrophin, thyroid hormones, growth hormone, insulin and insulin-like growth factors. An overview of the determinants of fecundity, with particular reference to oocyte recruitment and atresia, is the focus of the second part of the paper. Genetics and nutrition have major effects on fecundity, and studies so far suggest that the determinants of fecundity usually operate during the early part of gametogenesis. The role of atresia in determining fecundity is less clear. The final part of this review highlights some areas of study that are priorities for research on ovarian development in fish.     

Spatial and environmental effects on Coho Salmon life history trait variation

Adult size, egg size, fecundity, and mass of gonads are affected by trade‐offs between reproductive investment and environmental conditions shaping the evolution of life history traits among populations for widely distributed species. Coho salmon Oncorhynchus kisutch have a large geographic distribution, and different environmental conditions are experienced by populations throughout their range. We examined the effect of environmental variables on female size, egg size, fecundity, and reproductive investment of populations of Coho Salmon from across British Columbia using an information theoretic approach. Female size increased with latitude and decreased with migration distance from the ocean to spawning locations. Egg size was lowest for intermediate intragravel temperature during incubation, decreased with migration distance, but increased in rivers below lakes. Fecundity increased with latitude, warmer temperature during the spawning period, and river size, but decreased in rivers below lakes compared with rivers with tributary sources. Relative gonad size increased with latitude and decreased with migration distance. Latitude of spawning grounds, migratory distance, and temperatures experienced by a population, but also hydrologic features—river size and headwater source—are influential in shaping patterns of reproductive investment, particularly egg size. Although, relative gonad size varied with latitude and migration distance, how gonadal mass was partitioned gives insight into the trade‐off between egg size and fecundity. The lack of an effect of latitude on egg size suggests that local optima for egg size related to intragravel temperature may drive the variation in fecundity observed among years.     

Gonad development and size‐at‐maturity of silver therapon Leiopotherapon plumbeus (Kner 1864; Teleostei:Terapontidae) in tropical volcanic lakes in south Luzon,Philippines

Gonad development of the silver therapon Leiopotherapon plumbeus in two volcanic crater  lake  habitats (Sampaloc Lake, Taal Lake) in south Luzon, Philippines was examined during the annual reproductive cycle. The minimum body size‐at‐maturity of fish in these two lake habitats was also compared. Four gonad development stages were characterized as basis for the classification of ovarian (immature, maturing, mature, spawned) and testicular maturation (immature, maturing, mature) phases. The occurrence of all development stages in individual gonads suggest an asynchronous development whereby advanced stages are recruited continuously from a pool of younger stage germ cells to result in elevated female and male GSI throughout the annual cycle due to active gonadogenesis. Together with the increasing occurrence of advanced stage oocytes and spermatozoa from March until October, the elevated GSI of fish may indicate peak gonadal growth during the onset of the dry season (December–January) for eventual spawning from the beginning (May–June) until the end of the wet season (October–November). In both lake habitats, male fish were smaller than females but, regardless of sex, the minimum size‐at‐maturity of fish in Sampaloc Lake was significantly smaller than fish in Taal Lake. Overall, asynchronous development during oogenesis and spermatogenesis allows for year‐round reproduction of silver therapon, with elevated gonad growth in the dry season in preparation for spawning during the wet season. Compared with fish in Taal Lake, a smaller size‐at‐maturity of fish in Sampaloc Lake may be a response of the wild fishery stock to long‐term high fishing mortality and degradation of the lake habitat.     

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 tothe square of the total length in centimetres of the parent fish. The brood numbers of 460 femalesare 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 anestimate 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.     

Life history patterns of a livebearing fish in contrasting environments

Summary The population dynamics and energy allocations of the Gila topminnow, a small livebearing fish, were studied in two contrasting environments, a spring run of constant characteristics and a fluctuating desert wash. Topminnows grew and matured in two basic patterns. First, many fish in both areas matured the year after their birth. Second, spring fish born early in the breeding season grew rapidly, bred within five months, and died by eight months of age. Although spring fish assimilated more energy, wash fish actually expended more calories for growth and reproduction, partly because of lower maintenance costs. Reproductive effort of long-lived spring fish varied with age between 3.1 and 6.5%; whereas efforts of short-lived spring and wash fish increased steadily with age to 5.2 and 9.8%, respectively. Although spring fish produced eggs of higher energy content, females in both areas varied their investment per offspring, apparently tracking seasonal changes in the availability of food for fry. When long-lived spring fish experienced food shortage, they allocated less energy to both growth and reproduction; in contrast, wash and short-lived spring fish under similar conditions reduced only their growth allocation. The reproductive mass in spring fish appeared to be limited by food availability, incompletely filled the abdominal space, and reflected no tradeoff between fecundity and investment per offspring. Reproduction by wash fish appeared to be limited by body space and was characterized by a tradeoff between fecundity and egg size.     

Age, growth and reproduction of the cyprinid Rutilus lemmingii (Steindachner, 1866) in the River Huebra, Central Spain

Age, growth and reproduction of the R. lemmingii population of the River Huebra, Duero basin are analysed. Females dominated older age classes and lived up to 6 years (5+) while males only reached 5 years (4+). The growing season extended from April to September; growth rates were similar for both sexes. 0+ fish condition increased during their first summer and spring. In older fish, condition cycle was related to gonad development and showed some differences between sexes. The number of females reaching maturity at age 1 + almost doubled that of males; females also matured at smaller size. Both fecundity and egg size increased with female length: mean egg counts varied between 974 for 1 + individuals and an estimated 10491 for 5+ fish. Eggs were produced as a single batch, but were released fractionally during April and May.     

Maturation at a young age and small size of European smelt (<Emphasis Type="Italic">Osmerus eperlanus</Emphasis>): A consequence of population overexploitation or climate change?

Age of fish at maturation depends on the species and environmental factors but, in general, investment in growth is prioritized until the first sexual maturity, after which a considerable and increasing proportion of resources are used for reproduction. The present study summarizes for the first the key elements of the maturation of European smelt (Osmerus eperlanus) young of the year (YoY) in the North-eastern Gulf of Riga (the Baltic Sea). Prior to the changes in climatic conditions and collapse of smelt fishery in the 1990s in the Gulf of Riga, smelt attained sexual maturity at the age of 3–4 years. We found a substantial share (22%) of YoY smelt with maturing gonads after the collapse of the smelt fisheries. Maturing individuals had a significantly higher weight, length and condition factor than immature YOY, indicating the importance of individual growth rates in the maturation process. The proportion of maturing YoY individuals increased with fish size. We discuss the factors behind prioritizing reproduction overgrowth in early life and its implications for the smelt population dynamics.     

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.     

A field experiment on the effects of interspecific competition from roach, Rutilus rutilus (L.), on age at maturity and gonad size in perch, Percafluviatilis L.

The effects of interspecific competition from roach on gonad development in O+ and 1+ perch were studied in a pond experiment by varying the roach density between treatments. The proportion of mature O+ males first increased and, thereafter, decreased with increasing roach density and increasing somatic weight. O f females were immature and all I+ males were mature. The proportion of mature 1+ females decreased with increasing roach density and decreasing somatic weight. The gonad weight of O+ and 1+ males as well as 1+ females decreased with increasing roach density and decreasing somatic weight. For 1+ males, which were individually marked, both start weight as well as somatic end weight were positively related to gonad weight. One possibleexplanation for the hump shaped relationship between the proportion of mature O+ males and somatic weight is that behavioural interactions between O+ and I+ males in the absence of roach affected maturing in O+ males. This study supports previous suggestions that annual variation in resource availability may give rise to variance in fecundity-body size relationships.     

Life-history plasticity under resource stress in a clonal fish (Poeciliidae: Poeciliopsis)

Within-individual plasticity for reproductive investment was examined in a clonal fish (Poeciliidae: Poeciliopsis) grown under six levels of resource stress. Growth, age at first reproduction, egg production, egg size, egg energetic content, and survivorship were measured from fish grown in three dietary and two density treatments. Growth and fecundity decreased with both increased density and food stress. Age at first reproduction increased with increased density, but was unaffected by the diet treatments. Reproductive effort (clutch size per female weight), offspring investment (egg size and egg energetic content), and survivorship were invariant across all treatment combinations. We compare these results with predictions based on theoretical treatments of optimal reproductive investment.     

Landscape‐scale life‐history gradients in New Zealand freshwater fish

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