Patterns of oocyte growth, vitellogenin and gonadal steroid concentrations in greenback flounder

The pattern of oocyte development in association with changes of plasma concentrations of vitellogenin (Vtg), 17β‐oestradiol (E₂) and testosterone (T) was investigated in maturing female greenback flounder Rhombosolea tapirina over the first part of a reproductive season (February to June). Examination of oocyte size‐frequency distributions showed that the oocyte developmental pattern in R. tapirina is multiple group synchrony, and that reproductively mature fish were present at all sampling times. There were no significant temporal variations in the gonado‐somatic index ( I _G), hepato‐somatic index ( I _H), or plasma concentrations of Vtg, E₂ and T during the sampling period, which indicates that reproductive development is not synchronized within the population. Significant increases in I _G, I _H and plasma concentrations of Vtg, E₂ and T, however, were observed in vitellogenic fish, and in fish undergoing final maturation. A positive relationship was also found between the growth of oocytes and plasma concentrations of Vtg, E₂ and T, although the patterns of increase were different for each variable. Plasma concentrations of Vtg and E₂ rose steadily across oocyte sizes from 100 to 450 μm, but the rate of increase of plasma E₂ was slower than that of Vtg, and both reached a saturated concentration at oocyte sizes of c . 450 μm. In contrast, plasma concentrations of T showed no marked increase until oocytes grew beyond 400 μm.     

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

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

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

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

Morphological and histological changes in the swim bladder during maturation of the Japanese eel

Silver eels Anguilla japonica ( I _G 1·5–3·5) had more developed rete mirabile, gas gland and submucosa than yellow eels ( I _G 0·4–1·5) and the development of swim bladder components increased with sexual maturity only in the early maturation process ( I _G 3·5). These observations indicate that the Japanese eel develops its swim bladder in either the river or shallow sea water and leaves for the open sea after the swim bladder has become adapted to a deeper-sea environment.     

Gape morphology of cod Gadus morhua L., haddock Melanogrammus aeglefinus (L.) and whiting Merlangius merlangus (L.) through metamorphosis from larvae to juveniles in the western Irish Sea

Variations in standard length ( L _S), gape size ( S _G) and jaw length ( L _J) were studied in larval and juvenile gadoids (cod Gadus morhua , haddock Melanogrammus aeglefinus and whiting Merlangius merlangus ) from 4 to 70 mm. The increase in S _G and L _J was not linear with respect to L _S. The relationship was best described by segmented regression lines in all three species, with an inflection point at c . 10·5 mm. The S _G and L _J increased more rapidly in relation to larval L _S for individuals smaller than this inflection point size. The rates of increase slowed significantly post-inflection, an effect more noticeable in S _G data compared to L _J data. In each case, the inflection point fell in the intermediate period of development between the larval and juvenile stages, which could be considered as metamorphosis. Published equations that have been used to predict S _G from L _J lead to the overestimation of gape. New relationships are presented, which may be used to predict S _G from measurements of either L _S or upper jaw length in cod, haddock and whiting.     

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

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

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

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

Changes in reproductive physiology and behaviour over the nesting cycle in male three‐spined sticklebacks

Plasma 11‐Ketotestosterone (11 KT) and testosterone (T) levels and spiggin‐mRNA levels, as well as the kidney‐somatic index ( I _K) were measured in sexual males and in paternal males at the middle (5 days paternal) and at the end (8 days paternal with hatched eggs) of the nesting cycle in three‐spined sticklebacks Gasterosteus aculeatus from two populations. Glueing (using threads of 11 KT induced kidney‐protein spiggin) and fanning behaviour was measured daily. Fanning increased in paternal fish and remained low in sexual males. Plasma 11 KT and T levels, on the other hand, declined significantly in parental compared to sexual males as did spiggin expression, I _K and glueing behaviour. Thus, the drastic decrease in circulating 11 KT levels during the later parental phase may have resulted in an energy‐saving decrease in spiggin‐production and glueing, when this was no longer needed for nest maintenance. In addition, the mRNA levels of the β‐subunits of both gonadotropins, luteinising hormone (LH) and follicle stimulating hormone (FSH) were measured. The expression of both gonadotropins declined in the parental phase (not significant for β‐FSH in one of the populations) which was consistent with a decline in androgen levels possibly controlled via decreased gonadotropin secretion.     

The reproductive biology and ecology of the Port Jackson shark Heterodontus portusjacksoni in the coastal waters of eastern Australia

The reproductive biology and ecology of the Port Jackson shark Heterodontus portusjacksoni was investigated at three locations on the central and southern coast of New South Wales (NSW), Australia from January 2002 to December 2005 using underwater visual census surveys and samples obtained from a commercial fishery. Adults displayed sexual dimorphism in total length ( L _T) at sexual maturity, with males maturing between 762 and 772 mm L _T and females between 902 and 905 mm L _T. The mean ovarian fecundity was estimated at 16 offspring per female but was unrelated to female L _T. Male gonado-somatic ( I _G) and hepato-somatic ( I _H) indices and female I _G declined from July to November as did maximum ovarian follicle diameter and the diameter of the three largest follicles. Adults were absent from inshore reefs between December and July. Hence, H. portusjacksoni has a synchronous annual breeding season in NSW, which occurs between July and November (the austral winter to spring), with a peak in oviposition from August to October. Heterodontus portusjacksoni copulatory and ovipository behaviour are reported for the first time. Copulation was observed and involved oral grasping of the female's pectoral fin by a single male, which wrapped his body around hers to insert one clasper. Ovipositing females appeared to search crevices in the reef prior to delivering a single capsule, which was washed into the crevice by water movement, with the female departing very soon after oviposition. This study represents the first rigorously quantitative analysis of H. portusjacksoni reproductive biology and ecology in NSW waters.     

Ovarian morphology of the Japanese eel in Mikawa Bay

Annual changes in gonadal maturation of female Japanese eel Anguilla japonica in sea water were investigated histologically over 5 years in the Mikawa Bay, Japan, where they occurred throughout the year except in March. Almost all immature Japanese eels (yellow eels) occurred mainly from April to September, and they were rare after November. In contrast, maturing Japanese eels (silver eels) occurred from October to February. The gonado‐somatic index ( I _G) and oocyte diameters of yellow eels were <1·0 and 150 μm, respectively, and oocytes were at the peri‐nucleolus or the oil droplet stages. The I _G and oocyte diameters of silver eels were greater than those of yellow eels and most oocytes developed to the primary yolk globule stage. The numbers of silver eels lacking oocytes at the primary yolk globule stage increased after January in Mikawa Bay, although I _G and oocyte diameters remained unchanged. In contrast, silver eels caught at the mouth of the bay in January possessed oocytes that had advanced to the secondary yolk globule stage. These observations indicate that oocyte development changes seasonally, especially after winter in Mikawa Bay.     

Latitudinal variability in lunar spawning rhythms: absence of a lunar pattern in the northern mummichog Fundulus heteroclitus macrolepidotus

In this study, the natural spawning season of the northern mummichog Fundulus heteroclitus macrolepidotus was examined from May to July in the lower St John River, New Brunswick, Canada (45° N), through measurements of gonado-somatic index ( I _G), liver-somatic index ( I _L) and condition factor ( K ). I _G increased during the prespawning phase (mean ± s.e. 5·49 ± 0·20%), peaked during the spawning phase (14·68 ± 0·51%) and dropped during the regression phase (3·23 ± 0·29%). A single peak of spawning was observed in F. h. macrolepidotus , contrasting with multiple peaks observed in studies south of 41° N in North America. Within the prespawning phase, there were significant differences between sampling dates in female body mass, gonad mass, liver mass and K . On the basis of results from this study, water temperature is believed to be the predominant factor controlling initiation of spawning in F. h. macrolepidotus .     

Plasma non-esterified fatty acid profiles in wild Atlantic salmon during their freshwater migration and spawning

Total plasma non-esterified fatty acid (NEFA) levels increased significantly in adult Atlantic salmon during the first months of their upstream migration and spawning in the Exploits River, Newfoundland, Canada. The highest levels occurred in May and were 5467±270·43 nmol ml⁻¹ for females and 4617±334·70 nmol ml⁻¹ for males. Significantly higher levels were maintained by females compared with males for most of the upstream migration. Between August and October, total plasma NEFA levels declined by 61% in females but only 23% in males. The decline in plasma monounsaturated and polyunsaturated fatty acid levels accounted for 74% of the loss of NEFAs in females. Specific plasma NEFAs such as 16: 0 (palmitic), 16: 1 (palmitoleic), 18: 1n9 (oleic) and 20: 5n3 (eicosapentaenoic acid) differed significantly between males and females during migration and spawning. The mean gonadosomatic index ( I _G) values of females in May and just prior to spawning were 0·37±0·01 and 10·25±0·32, respectively. The rapid decline in the plasma NEFA content of females coincided with the largest increase in their I _G (1·85±0·02–10·25±0·32). Corresponding I _G values for males were 0·34±0·01 in May and 3·33±0·78 prior to spawning. Plasma NEFA levels of spent salmon did not differ between sexes and were significantly lower than those of salmon preparing to spawn.     

Life-history traits of introduced Iberian pumpkinseed Lepomis gibbosus relative to native populations. Can differences explain colonization success?

To assess the colonization success of pumpkinseed Lepomis gibbosus on the Iberian Peninsula, life-history attributes of pumpkinseed populations from Spanish water bodies were compared to populations in the northern and southern parts of its native range, as well as to those of English water bodies where introduced populations have shown minimal natural range expansion. Discriminate function analysis using five population characteristics [mean age at maturity, mean total length ( L _T) at maturity, gonado-somatic index ( I _G), mean L _T at age 2 years as an indication of juvenile growth rate and relative body condition] strongly differentiated populations from the four regional study areas. Spanish populations were early maturing, showed moderate juvenile growth rate and L _T at maturity and high I _G relative to the other population groups. Spanish populations matured significantly earlier than Canadian and English populations, but not southern U.S.A. populations. Spanish populations, however, had a significantly higher I _G than southern U.S.A. populations, suggesting greater reproductive output. Considering these differences in the context of the Winemiller and Rose triangular life-history strategy model, the pumpkinseed exhibits 'equilibrium' life-history traits that have made other non-native fishes successful invaders in areas where habitat alteration has resulted in more predictable discharge regimes and water levels. Populations in Iberia, however, appear to have achieved their success by adopting a more 'opportunistic' life-history strategy than their native counterparts. High levels of life-history plasticity appear to contribute to the success of this species on the Iberian Peninsula.     

Histological classification of oocyte growth and the dynamics of ovarian recrudescence in Tilapia zillii

Serum levels of 17β-oestradiol and testosterone peaked and fell within 6 days of spawning in Tilapia zillii suggesting that vitellogenic growth began as early as day 2 or 3 postspawning. As early as day 8, stage 6/7 (late nitellogenic and maturing) oocytes occupied 60–70% of the ovary. From day 8 onwards the proportion of stage 6/7 oocytes changed little, though I _G increased (as oocytes grew) to reach maximal levels of ∼ 5·5% by day 14. I _G was correlated significantly to the proportion of stage 6/7 oocytes. Postovulatory follicles were observed immediately following spawning occupying up to ∼ 7% of the ovary but were not present from day 3 onwards. Atretic oocytes were found throughout the time period monitored (generally occupying <2% of the ovary) but were more prevalent from day 18 onwards. Data suggest that previtellogenic oocytes are recruited into vitellogenic growth immediately after spawning and can complete vitellogenesis as early as day 8 postspawning. Knowledge of this timing is likely to be important in the development of spawning induction programmes in T. zillii and other related species.     

Genetic variation, its assessment and implications to the conservation of seagrasses

In a study of the widespread Australian endemic seagrass Posidonia australis , allozyme analysis identified a wide range in population genetic structure assessed using the multilocus genotype diversity statistic ( D _G). Values of D _G between zero and one were obtained; however, RAPD analysis generally detected higher levels of diversity, where D _G values were all greater than 0.5 ( D _G = 0.67 – 1). Some populations were allozymically monomorphic using allozyme analysis yet were highly polymorphic using RAPD analysis. The differences observed between methods, particularly among allozymically uniform populations, demonstrate the importance of choosing an appropriate method when assessing genotypic diversity. Different methods may reflect different historical aspects of population processes where allozymes reflect broader-scale gene flow and population establishment and DNA fingerprinting methods such as RAPDs may reflect fine-scale local recruitment events and shorter-term population processes. Using either method alone, particularly in genotypically depauperate organisms such as seagrasses and other clonal organisms, will be problematic in assessing their population genetic potential, a parameter being used by conservation managers to decide upon management strategies in rare and endangered organisms. It is recommended that the impact of disturbance assessed using genotypic diversity measures requires more than one technique to provide the most appropriate information for designing subsequent conservation strategies.     

Cell population kinetics of thyroid follicular cells in infant rats

Abstract. T cell population kinetics of thyroid follicular cells in rats were studied by means of autoradiography and a statmokinetic technique. During the first fortnight after birth no significant changes in the mitotic index (MI) and labelling index (LI) were found. In the next 2 weeks a constant decrease in the number of proliferating cells occurs. In 10-day old animals 40% of the follicular cells were in the cell cycle (GF); 3.25 ± 0.77 (SEM) % in the S phase and 0.18 ± 0.04% in mitoses (MI). Day–night changes in the LI and mitotic rate (MR) indicated a peak value at 13.30 hours with a lowest value at 22.30 hours. The mean LI and MR averaged over the whole 24 hr were 3.1 ± 0.1% and 122.2 ± 18.1%, respectively. In 10-day old animals, using the fraction of labelled mitoses (FLM) method the median cell cycle time ( T _C) was 79 hr and the phase durations were T _G1—64.6 hr, T _s—8.2 hr and T _G2—5.1 hr. The decrease in the number of proliferating cells with the age of the animals is considered to be a result of both cell cycle prolongation and in growth fraction reduction.     

Lipid content and fatty acid composition of target tissues in wild Perca fluviatilis females in relation to hepatic status and gonad maturation

Variation in liver ultra‐structure and composition in relation to energy mobilization was investigated in female perch Perca fluviatilis from the Meuse River between August 2001 and June 2002. In April, just before spawning, the lipo‐somatic index ( I _F) was 0·3%, the gonado‐somatic index ( I _G) was 28% and the total lipid content of the liver was 2·53%. The average areas of lipid droplets and mitochondria were 0·05 and 0·06 μm², respectively. Glycogen supply reached 7·9% of the total area of the hepatocyte. During the sexual resting period, females accumulated energy in perivisceral fat and in the liver to reach 1·6% I _F and 4·85% of liver lipid content in August with lipid droplets average size of 0·09 μm² and glycogen average area of 15%. Liver cells contained a weakly developed rough endoplasmic reticulum (RER) and a great number of small mitochondria (average size 0·02 μm²). The I _G was 0·6% at this time. During the whole annual cycle, the average lipid content of female liver never exceeded 3·9 ± 1·9%. The concentration of docosahexaenoic (DHA), linolenic and linoleic acids increased in mature gonads while linolenic and linoleic acids decreased in the liver during the same period. Fatty acid composition of muscles of perch was characterized by a high content of DHA.     

Metabolic costs of growth in free-living Garter Snakes and the energy budgets of ectotherms

1. The metabolic or respiratory cost of growth ( R _G) is the increase in metabolic rate of a growing animal, and it represents chemical potential energy expended in support of net biosynthesis but not deposited as new tissue.
2. Two statistical methods (multiple non-linear regression and analysis of regression residuals) were used to calculate R _G from data ( n = 68) from a doubly labelled water study of free-ranging Garter Snakes ( Thamnophis sirtalis fitchi ) in northern California.
3. The sample-wise ('ecological') cost of growth was 2·07 kJ per gram of net growth (equivalent to 8·63 kJ g^–1 dry tissue); reanalysis of a subset of efficient growers yielded a more conservative 'physiological' estimate of 1·67 kJ g^–1.
4. Our empirical estimate of R _G, among the first reported for squamate reptiles and free-living animals of any kind, compares closely with published, laboratory-derived values for ectotherms.
5. The metabolic costs of growth accounted for an average of 30% of total field metabolic rates for these snakes, which were growing at a mean rate of 3% of body mass per day. However, our method probably underestimated the total ecological cost of growth for large animals, because potential growth costs that covary with body size were not included.
6. Distinction between conceptual and empirical energy budgets clarifies relationships among body size, metabolic rates, and the physiological and ecological costs of growth.     

Reproductive cycle and sexual maturity of the anglerfish Lophiomus setigerus in the East China Sea with a note on specialized spermatogenesis

The reproductive cycle and sexual maturity of the anglerfish Lophiomus setigerus were examined. Spermatids were released from the germinal cysts into the lumina of the seminal lobules, and both spermatids and spermatozoa were present in the lumina of the seminal lobules and sperm ducts. Spermatogenesis and vitellogenesis occurred throughout most of the year. The testes of males were full of spermatozoa throughout the year, with spawning from May to November. Males and females reached sexual maturity at a mean total length and age of 178 mm, 3.3 years and 303 mm, 6.1 years, respectively. There were clear seasonal cycles in the gonadosomatic index (I_G) and hepatosomatic index ( I _H) in females. The mean I_G of females increased rapidly with ovarian development while the mean I _H decreased from the middle of vitellogenesis to final maturation. Mean values of I _G and I _H in males increased with testicular development.     

The influence of temperature on the onset of first maturity in sea bass

Oocyte development was aborted and full maturity did not occur in virgin female sea bass Dicentrarchus labrax unless they remained in water above 10° C during the main period of gonad development. There was no difference in the condition factors of females with high or low I _G values in March, which indicates that retarded gonadal development was not necessarily due to poor body condition or nutritional state. It is suggested that the extended duration of the adolescent phase of female bass around southern Britain is a response to their environment, rather than an intrinsic aspect of the species'biology.