Reproduction of the spiny puffer, Diodon holocanthus (Pisces: Diodontidae) in the continental shelf of Mexican Central Pacific

Diodon holocanthus is an important economic and ecological species of the demersal fish community, caught as bycatch from local shrimp fishery. The reproductive biology of this long-spine porcupinefish has not yet been described, and reproductive season, the sex ratio, length distribution, length at first gonad maturity, and the gonad macro and microscopic features are described. A total of 400 organisms, ranging from 5.0 to 40.3 cm (average 18.4 cm) total length, were caught from the continental shelf of the Central Mexican Pacific, from December 1995 and December 1998. Sex ratio was 1:0.86 females to males (n = 253). The length at which 50% of the individuals showed maturing gonads was 19.7 cm for females and 20.1 cm for males. Length of the smallest organism with ripe gonads was 12.2 cm for females and 13 cm for males. Four gonadal maturation stages were found in both sexes, and five oocyte development phases were identified. The oocyte development pattern is of asynchronous type, which means the species can reproduce several times a year. Testicle development is lobular type, as in most teleost fishes. Monthly mean values of the gonad-somatic index suggest the reproduction activity peaks in June, and September-December.     

Annual variation in energy reserves in male three-spined stickleback, Gasterosteus aculeatm L. (Pisces, Gasterosteidae)

Wet and dry weights of tissue were measured and concentrations of glycogen, lipid and protein were estimated for the liver, gonad and carcass of male sticklebacks from an annual population collected each month over one complete year. In young-of-the-year there is one period of rapid weight gain, in all three body regions (liver, carcass and gonads) but particularly of the carcass, in the autumn and a second in spring and early summer. This is accompanied by an increase in the water content of all three body regions. The gonadosomatic index also increases sharply in spring and early summer. Young sticklebacks accumulate lipid and glycogen slowly during the autumn and winter of their first year of life and more rapidly from late winter to early summer. Thus, the period of most rapid accumulation of these reserves coincides with the time when body weight and gonad maturation are also increasing sharply. Lipid and glycogen levels fall during the reproductive season in those males that breed, so that by July they are reduced to 43% and 37% (respectively) of their peak values in May. Levels of protein increase throughout the year as the fish grow, but in breeding males by July the concentration of protein in the carcass falls to 70% of pre-breeding levels. Breeding males therefore reach the end of the reproductive season with their total energy reserves severely reduced, and consequently they suffer a very high mortality. In contrast, adult males that fail to reproduce survive beyond the breeding season. They continue to gain weight and to accumulate lipid and glycogen from August to September, but these energy reserves fall (to levels comparable to those of post-breeding fish) in December, when these fish probably die. These results demonstrate that in male sticklebacks, growth and gonad maturation can be sustained in parallel with the accumulation of energy reserves, which are subsequently extensively depleted as a result of reproductive activities.     

Gonad growth in the sea urchin, Strongylocentrotus purpuratus (Stimpson) (echinodermata: Echinoidea) and the assumptions of gonad index methods

In central Oregon intertidal populations, the echinoid Strongylocentrotus purpuratus (Stimpson) first begins to produce mature gametes at a diameter of 25 mm during the second year of its life. All individuals above 40 mm in diameter have mature gametes during the mid-winter spawning season. Gonad size increases rapidly relative to body size until the animals are ≈45 mm in diameter and have a total dry weight of ≈ 15 g. The ratio of gonad to body size reaches its maximum in animals between 40 mm and 50 mm in diameter; thereafter the ratio drops slightly with increasing size. The curvilinear relation between gonad size and body size is not related to a relative difference in body proportions with size. Internal volume, height, and diameter increase linearly with size. Body proportions did not differ between the two populations studied. Differences between populations in the ratio of gonad to body size extend to all sizes in the populations and the direction but not the amount of the difference is consistent from year to year. These differences between habitats are probably related to food supply. The use of gonad ratio methods to normalize gonad size assumes that, within a given population, animals of different body size have the same ratio of gonad size to body size. This assumption is not correct for four species of sea urchins. Gonad index or ratio methods are useful for comparing animals of the same size through time within a population or from different habitats. Restriction of the size range of animals used and use of samples of sufficient size permit gonad ratios to be used to assess the capacity of different habitats to support gonad production in sea urchins and other animals.     

Anatomical changes to the gonad during protogynous sex change in the half-moon grouper Epinephelus rivulatus (Valenciennes)

Anatomical changes to the gonad during sex change in the protogynous grouper Epinephelus rivulatus are described from histological observations. A decrease in ovarian mass occurred soon after the onset of sex change as oocytes atrophied and were removed from the gonad. Blood supply and abundance of unidentified somatic cells increased at this time as proliferation of sperm tissue commenced. As the gonad was cleared of ovarian tissue, the rate of spermatogenesis increased and the lamellae soon became dominated by sperm and connective tissue. Putative Leydig cells, the probable sites of male steroid production, appeared in transitional gonads and were most abundant in the testes of immature males. Peripheral sperm sinuses subsequently formed within basal tissue layers of the tunica and expanded as they filled with spermatids. The process of sex change, occurring as a result of experimental manipulation of wild populations at the start of the spawning season, took c. 3 weeks. This appears rapid compared to other hermaphroditic species and may reduce the impacts of fishing on reproductive output by E. rivulatus populations.     

Activity budgets and activity rhythms in red ruffed lemurs (Varecia rubra) on the Masoala Peninsula, Madagascar: seasonality and reproductive energetics

The activity budgets and daily activity rhythms of Varecia rubra were examined over an annual cycle according to season and reproductive stage. Given the relatively high reproductive costs and patchy food resources of this species, I predicted that V. rubra would 1) travel less and feed more during seasonal resource scarcity in an attempt to maintain energy balance, and 2) show sex differences in activity budgets due to differing reproductive investment. Contrary to the first prediction, V. rubra does not increase feeding time during seasonal food scarcity; rather, females feed for a consistent amount of time in every season, whereas males feed most during the resource-rich, hot dry season. The results are consistent with other predictions: V. rubra travels less in the resource-scarce cold rainy season, and there are some pronounced sex differences, with females feeding more and resting less than males in every season and in every reproductive stage except gestation. However, there are also some provocative similarities between the sexes when activity budgets are examined by reproductive stage. During gestation, female and male activity budgets do not differ and appear geared toward energy accumulation: both sexes feed and rest extensively and travel least during this stage. During lactation, activity budgets are geared toward high energy expenditure: both sexes travel most and in equal measure, and rest least, although it remains the case that females feed more and rest less than males. These similarities between female and male activity budgets appear related to cooperative infant care. The high energetic costs of reproduction in V. rubra females may require that they allot more time to feeding year round, and that their overall activity budget be more directly responsive to seasonal climate change, seasonal food distribution, and reproductive schedules.     

Ovarian activity and plasma sex steroid levels of Distichodus antonii in relation to environmental conditions in the upper basin of the Congo River

Distichodus antonii is an endemic fish species of the Congo River basin in which the stocks of wild populations are threatened by overfishing pressure. Knowledge of its reproductive biology would be useful in consideration of conservation and management options for the species. Therefore, this study investigated changes in ovarian activity and levels of steroid profiles in wild populations in relation to variation in temperature and rainfall. Adult females (n = 101, body weight of 3 183 ± 14.75 g, SE) were captured monthly over one year (2013–2014). Apart from evaluation of oocyte diameters and gonad developmental stages, gonado-, hepato-, lipososomatic indices (GSI, HSI, LSI) and plasma levels of sex steroids (testosterone-T, estradiol-17β-E2) were determined. The results suggested a synchronous development of oocytes with two annual reproductive seasons over the one-year study. Plasma T and E2 levels peaked during spawning periods likely reflecting active oogenesis. The highest values of morphosomatic indices were observed during the longest rainfall period in September, and were associated with high steroidogenic activity evidenced by increased E2 production. In addition, more vitellogenic oocytes (September and October) were observed during the latter season than during the short rainy season (in May).     

A tropical oviparous lizard, Calotes versicolor, exhibiting a potentially novel FMFM pattern of temperature-dependent sex determination

Among squamate reptiles, lizards exhibit an impressive array of sex-determining modes viz. genotypic sex determination, temperature-dependent sex determination, co-occurrence of both these and those that reproduce parthenogenetically. The oviparous lizard, Calotes versicolor, lacks heteromorphic sex chromosomes and there are no reports on homomorphic chromosomes. Earlier studies on this species presented little evidence to the sex-determining mechanism. Here we provide evidences for the potential role played by incubation temperature that has a significant effect (P < 0.01) on gonadal sex and sex ratio. The eggs were incubated at 14 different incubation temperatures. Interestingly, 100% males were produced at low (25.5 ± 0.5 ° C) as well as high (34 ± 0.5 ° C) incubation temperatures and 100% females were produced at low (23.5 ± 0.5 ° C) and high (31.5 ± 0.5 ° C) temperatures, clearly indicating the occurrence of TSD in this species. Sex ratios of individual clutches did not vary at any of the critical male-producing or female-producing temperatures within as well as across the seasons. However, clutch sex ratios were female- or male-biased at intermediate temperatures. Thermosensitive period occurred during the embryonic stages 30-33. Three pivotal temperatures operate producing 1:1 sex ratio. Histology of gonad and accessory reproductive structures provide additional evidence for TSD. The sex-determining pattern, observed for the first time in this species, that neither compares to Pattern I [Ia (MF) and Ib (FM)] nor to Pattern II (FMF), is being referred to as FMFM pattern of TSD. This novel FMFM pattern of sex ratio exhibited by C. versicolor may have an adaptive significance in maintaining sex ratio.     

Seasonal changes in the chemical composition of fish body and nutritional value of the muscle of the pollan (Coregonus pollan Thompson) from Lough Neagh,Northern Ireland

Studies on the chemical composition of adult pollan were carried out monthly from January to December 1977. Sex, weight of scaled fillet, and gonads were examined in 184 fish. Chemical composition which includes water, fat and ash content was analysed in the whole fish, muscle and gonads. This paper attempts to account for the fat and protein flow within fish of both sexes during gonad maturation. Extreme differences between males and females have been recorded in the fat deposition process during summer and spawning period. In spite of our fragmentary knowledge of spawning behaviour in pollan, an explanation is offered for these phenomena. The changes in fat content of female gonads were followed closely throughout the year and the cost of egg production was estimated as a percentage of the amount of fat deposited in the body. Since a similar growth pattern was found for both sexes of pollan, differences in feeding intensity might account for the difference in energy expenditure. Amino acid content was analysed in muscle and gonads and an Essential Amino Acid Index (EAAI) was calculated. There were some changes in EAAI which depended on sex and season. Finally, a new method for evaluation of muscle production expressed as fat and protein is used to determine the most suitable time for fish harvesting.     

Reproductive traits and relative gonad expenditure of the sexes of the free spawning Chiton articulatus (Mollusca: Polyplacophora)

ABSTRACT

Reproductive studies of an intertidal free-spawning population of Chiton articulatus (Mollusca: Polyplacophora) from Puerto Angel, Oaxaca, Mexico were undertaken during 2011. We used gonad histology and gonadal indices to assess the relative gonad expenditure of the sexes (RGES) and other reproductive traits, accounting for individual and seasonal variation within this population. At this location, C. articulatus is gonochoric, without sexual dimorphism, except internally by gonad colour (testis is ‘salmon’ coloured and ovary olive green). Annual and monthly sex ratios (m/f) do not differ significantly from 1:1. Highest population-level gonadosomatic index (GSI) corresponded to maximum (peak) ripe stage (i.e. maximum gonad investment), with a first peak in May with a high value (8.4 ± 0.5) and a second peak during August-September with a lower value (4.7 ± 0.3). GSI fluctuated throughout year implying that gonad expenditure may be seasonally constrained, but with overall synchrony between sexes of ripe and spawning stages. July to December was the main reproductive season with some facultative spawning occurring off-season. Ripe and spawning RGES did not differ between sexes, suggesting that either sperm competition is intense and/or that sperm limitation is high. Early spawning individuals may quickly replenish their gametes for a second phase of gamete release later.

Abbreviations: RGES: relative gonad expenditure of the sexes; GSI: gonadosomatic index; GDS: gonad developmental stages; MiMI: microscopic maturity index; SST: sea-surface temperature.     

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.     

Dietary variability in fishes: the roles of taxonomic, spatial, temporal and ontogenetic factors

In spite of the general use of diet data in ecological research, still very little is known about the relative roles of spatial, temporal and biotic (e.g. taxonomic identity, size, sex) factors in dietary variability of fishes. Here, we applied canonical correspondence analysis and variation partitioning to examine the roles of taxonomic, annual, seasonal, lake basin, habitat and ontogenetic (standard length, L _S) factors in the dietary variation of fishes in large and shallow Lake Balaton, Hungary. The analyses were performed at the assemblage (15 fish species) and the individual species levels, and based on high (24 fine resource categories) and low resolution (nine broad resource categories) diet data. As hypothesised, most of the explained variation related to interspecific differences, while the roles of sampling year, season, lake area, habitat and L _S proved to be unexpectedly low at the assemblage level. In addition, no regularity was found in how the relative roles of these factors change between fish species. The high ratio of the unexplained variation suggests that individual variations in foraging strategies and resource use of fishes and unascertained stochastic processes had a strong influence on dietary variability both at the assemblage and the individual species levels.     

Age,growth and reproduction of a population of spined loach,Cobitis taenia (L.)

751 specimens of spined loach, Cobitis taenia (L.), were collected and studied over the period October 1972–October 1974. The majority of the males were found to die at the end of the 2+ season and the majority of the females at the end of the 3+ season. Back calculations for length at age were carried out from otolith measurements and found to correspond closely to actual measurements. Males and females grew similarly up until the end of their 1+ year of life, with most rapid growth occurring in the first year. Females continued to grow rapidly up to 2+, the rate then being reduced; the males showed an increasingly reduced rate of growth after the 1+ year. Ford Walford plots gave L∞ results which corresponded closely in most cases with the largest observed specimens. Gonad development and maturation of males and females followed different patterns. Males matured during the 1 + year at a length of approximately 40 mm from which point their dry gonad weight remained at a steady 0.02–0.03% of the body weight. Females appeared to mature a year later and their ovary weight and oocyte diameter increased with fish age. A seasonal cycle in gonad development was evident in females. There was a greater proportion of females to males, especially in the older age group. Spawning time was estimated to be between June and July.     

Reproductive effort and efficiency in the female common goby, Pomatoschistus microps (Krøyer) (Teleostei: Gobioidei)

Reproductive effort and efficiency are terms which together help to describe the reproductive investment of spawning fish. In this paper they are applied to a small and abundant inshore fish, the common goby, Pomatoschistus microps (Kroyer), based on data collected from the wild, and by modelling likely breeding patterns. Wet calorimetry was used to determine the energy content offish tissue, and this allowed reproductive effort to be expressed as both an energy and a weight ratio of gonad to somatic body. The gonadosomatic index (GSI) calculated as an energy ratio was greater than that calculated as a dry "weight ratio". For ripe females the GSI (dry weight) at the onset of breeding was 67.5%. Theoretical and observed values of the maximum number of egg batches laid by a single female during a 16-week breeding season are 9-10, and this corresponds to a total caloric investment of almost 12 kJ. Estimates of the reproductive efficiency, using the dietary energy content during the breeding season, range from 28.2% to a maximum of 44.0%. These values are among the highest calculated for a fish species, and are in keeping with the long and intensive breeding strategy observed in the wild population.     

Relationship between breeding activity and rainfall for Swainson's Spurfowl,Pternistis swainsonii,within southern Africa,with specific reference to the Springbok Flats,Limpopo Province,South Africa

We collated the literature available on the breeding activity of the Swainson's Spurfowl Pternistis swainsonii and made use of reliable unpublished reports, nest record cards and field observations within the Springbok Flats, Limpopo Province, South Africa to establish breeding seasons and pairing behaviour. The onset of breeding (egg laying) is closely associated with rainfall, with male gonad development, population density and covey size (pairing behaviour), all correlated with rainfall. Peak breeding activity is from January–April in South Africa, February–May in Zimbabwe and March–June in Botswana. Egg laying has been recorded in all months and sporadic egg laying in the winter months is most likely the result of isolated rainfall. Mean clutch size is 5.2 eggs/hen (n = 140) with an incubation period of 23 days and brood hatching success and chick survival of 69.4% over the southern African sub-region. Current hunting seasons within Limpopo Province are in line with the recommended hunting season for this region and should remain unchanged: 15 June–30 September. The success of this phasianid can be attributed to its extended breeding season, high survival rate of hatchlings and the potential of birds to breed within their first year.     

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.     

Spatial and temporal distribution of tadpole assemblages (Amphibia,Anura) in a seasonal dry tropical forest of southeastern Brazil

We determined spatial and temporal distribution of tadpoles in 11 breeding habitats from Morro do Diabo State Park (MDSP), southeastern Brazil. Breeding habitats occupancy by tadpoles was tested to be different from a null model of random placement of species. We also tested whether tadpole occupancy in a given breeding habitat is organized according to different ecomorphological guilds, and we analyzed spatial partitioning of tadpoles among breeding habitats through similarity analysis. For temporal analysis we analyzed temporal partitioning of tadpole monthly occurrence also using similarity analysis, and assessed what climatic variable better predicts tadpole temporal occurrence in the MDSP, through regression analysis. Among tadpoles from 19 anuran species, distribution was different from a null model, but co-occurrence patterns among the breeding habitats did not differ among different guilds. However, breeding habitats with similar hydroperiods had similar species composition, which may be related to the reproduction patterns of species. Among the three climatic variables analyzed (rainfall, temperature, and photoperiod), temporal occurrence of monthly tadpole richness and abundance was correlated with temperature and rainfall. Most species were found only during the rainy season months, and overlap occurred within three groups of species. Thus, temporal distribution does not seem to be an important mechanism in species segregation at the MDSP, where the dry season is pronounced. In this case, spatial partitioning tends to be more important for species coexistence.     

Reproductive patterns of the Pacific oyster Crassostrea gigas in France

Summary

In France, national management programs focus research on understanding reproductive factors in Crassostrea gigas to confront problems of the oyster industry. However, little information has been documented in which reproductive patterns include sexual changes. The reproductive cycle of oysters at three sites of the Atlantic coast of France was examined from 1996 to 1998, and the seasonal variations in oocyte size-frequencies, and sex ratio were described. The results showed a synchronism within the population concerning reproductive behavior. Young oocytes are generated after spawning and show no apparent changes during winter. Growth of oocytes begins in spring and cells reach maturity in April-May and are ready for a single spawning season in June-July. Oocytes that were not released during spawning are reabsorbed within the gonad. The significant difference between sites is that spawning occurred 1 month later in the southern area. A modal analysis showed that oocyte populations in the sample individuals are primordially bimodal, but with polymodal occurrences in June-July, in some cases. Irregular alternative sexuality was detected at all sites, and hermaphrodites appear to be a transition phase that allows changes from male to female during early spring. Previous observations, together with the study of the development of oocyte cohorts over time, permit a hypothetical model concerning the kinetics of gametogenesis in C. gigas. The model suggests that primary oocytes are generated from energy supplied from degenerating, as well as young oocytes that do not reach the mature stage within the gonad during autumn-winter. It seems that, during vitellogenesis, there is disintegration of smaller cells coupled with transfer of energy to the larger oocytes, which continue to grow and mature.     

Food availability and sex reversal in Mytella charruana,an introduced bivalve in the southeastern United States

We studied the reproductive biology of Mytella charruana to determine the potential reproductive success of this newly introduced bivalve species from Central/South America. We analyzed gonad morphology, gametogenesis, and the sex ratios of introduced populations throughout a 12 month period. In the non‐native habitat M. charruana shows the same strategy of gametogenesis that had been observed in its native environment, which is an opportunistic type of gonadal cycle with gametes produced throughout the year. Instead, the spawning period of M. charruana along the southeastern US coast is extended compared to that found in the native environment. We determined the minimum size (shell length) of sexually reproductive mussels to be 1.25 cm. Interestingly, throughout the year the population samples were typically composed of a higher proportion of females. The female to male sex ratio varied within a wide range from 1:0 to 1:3.3. Upon this discovery we tested the effects of food availability on the gametogenesis of adult animals. The sex ratio of mussels collected from different locations and maintained in the laboratory with or without food changed toward a male‐bias under starvation conditions within a month. This is the first study directly showing that food availability can trigger sex reversal in an adult bivalve. According to our data this mussel species will likely continue to spread along the east coast of the US. Moreover, M. charruana may prove to be a model organism in the study of alternative sexuality in bivalves. Mol. Reprod. Dev. 77: 222–230, 2010. © 2009 Wiley‐Liss, Inc.