Gonadal Growth Research Articles

Effects of hypoxia on feed intake and gonad growth in the green sea urchin, Strongylocentrotus droebachiensis

The effects of oxygen content on gonad growth and feed intake in “green sea urchin”, Strongylocentrotus droebachiensis, were examined. Adult sea urchins with a mean (S.D.) live weight of 51.0 (12.2) g were reared at oxygen levels of 4.0, 6.0 (hypoxia) and 9.5 mg l − 1 (normoxia), for 54 days at 8.0 °C and 33‰. Gonad growth and total food consumption were significantly higher in the control group (normoxia) compared with the hypoxic groups at the end of the experiment. Weekly feed intake and total feed consumption were significantly reduced in the two hypoxic groups. The reduction in gonad growth was attributed to a decrease in feed intake and impaired food conversion efficiency. Overall, our findings suggest that adult green sea urchins show low tolerance to hypoxia, and are unable to maintain high gonad growth facing such conditions.

Exogenous T3mimics long day lengths in Siberian hamsters

Siberian hamsters (Phodopus sungorus) exhibit seasonal cycles of reproduction driven by changes in day length. Day length is encoded endogenously by the duration of nocturnal melatonin (Mel) secretion from the pineal gland. Short-duration Mel signals stimulate reproduction and long-duration signals inhibit reproduction. The mechanism by which Mel signals are decoded at the level of neural target tissues remains uncharacterized. In Siberian hamsters, exposure to short day lengths or injections of Mel in long days results in a decrease in hypothalamic expression of type 2 iodothyronine deiodinase (Dio2) mRNA. Dio2 catalyzes the conversion of the thyroid hormone thyroxine to triiodothyronine (T3). Thus exposure to short and long day lengths should decrease and increase hypothalamic T3 concentrations, respectively. We tested the hypothesis that exogenous T3 administered to short-day hamsters would mimic exposure to long day lengths with respect to gonadal stimulation. Hamsters gestated and raised in short day lengths that exhibited photoinhibition of the testes were given daily subutaneous injections of T3 or saline vehicle for 4 wk beginning at week 12 of life. The results indicate that exogenous T3 induced gonadal growth in short-day hamsters and delayed spontaneous gonadal development by an interval equal to the number of weeks during which T3 was administered. T3 injections delayed gonadal regression if given coincident with the transfer of hamsters from long to short day lengths. These results suggest that T3 mimics long day exposure in Siberian hamsters and may serve as an intermediate step between the Mel rhythm and the reproductive response.

Reproductive cycle and energy allocation of Octopus vulgaris in Galician waters, NE Atlantic

Reproductive and energy allocation analyses were performed on 1418 common octopus ( Octopus vulgaris) from the Galician creel fishery (NE Atlantic) between May 2000 and December 2005. Individuals ranged from 8 to 35 cm dorsal mantle length (DML) and 136–6303 g body weight (BW). The length–weight relationship for whole animals was BW = 2.9(±1.1) × DML 2.17(±0.04) ( r = 0.86; P < 0.00001). The sex ratio only differed from 1:1 during May and September. Spawning of O. vulgaris in this area extends from December to September with a unique peak in spring months. Size-at-maturity was 1788 g for females ( n = 508); and 903 g for males ( n = 467). Mean (±S.D.) potential fecundity was estimated at 221,447 ± 116,031 oocytes and mean oocyte length at 3.0 ± 0.8 mm. The mean number of fully developed spermatophores was 182 ± 88 with mean length of 48.8 ± 10.6 mm. Potential fecundity was significantly correlated with length and weight in both sexes. The condition (digestive gland to body weight ratio) of females increased proportionally with maturity stage and mature individuals had higher gonad investment suggesting that energy for gonad growth was derived from the diet rather than endogenous reserves. On the other hand, mature males showed poorer condition. The general picture of the reproductive biology of this species in Galician waters is discussed taking into account the seasonal wind-driven upwelling that governs this ecosystem.

Effect of variation in the protein value of the red macroalga Palmaria palmata on the feeding, growth and gonad composition of the sea urchins Psammechinus miliaris and Paracentrotus lividus (Echinodermata)

The sea urchins Psammechinus miliaris and Paracentrotus lividus were fed three macroalgal diets with varying protein content over a 90-day period. These diets were the red alga Palmaria palmata, which had been grown in seawater enriched with two levels of ammonia-N and contained a protein content of either 41% (High-N) or 32% (Low-N) and the brown alga Laminaria saccharina (23% protein). A significantly different response to the macroalgal diets by the two sea urchin species was found in terms of food consumption rate, food conversion efficiency, gonadal growth and gonad nutritional composition. P. miliaris was able to efficiently utilise the High-N P. palmata, whereas P. lividus exhibited a higher food conversion efficiency (FCE) and specific growth rate (SGR) when fed the Low-N compared with the High-N P. palmata. P. miliaris had a significantly higher food consumption rate and higher gonad index (GI) compared with P. lividus, irrespective of diet type. The lowest FCE, SGR and GI were shown by both species fed L. saccharina. No interspecific difference in gonadal nitrogen content was observed, although a positive relationship was shown between dietary and gonadal nitrogen content for both species. All three macroalgal diets produced bright orange or yellow orange gonad colour in P. lividus. High-N and Low-N P. palmata improved gonad colouration in P. miliaris compared with L. saccharina. The results suggest that P. miliaris can efficiently assimilate high protein plant-based diet, whereas P. lividus is less capable of benefiting from high dietary protein levels and this should be taken into consideration when culturing this species either in land-based or sea-based polyculture systems.

Society for Reproductive Biology Founders' Lecture 2007. Insights into germ cell biology: from the bench to the clinic

The germline is unique among tissues in being the only lineage that is transmitted through generations. The gonadal somatic cells that interact with male and female germ cells are equally important for their juxtacrine and paracrine signalling pathways that lead to the formation of functionally mature gametes and healthy progeny. The present review summarises exciting new studies that our group and others have achieved at the frontier of male and female germ cell biology and in studying transforming growth factor-beta signalling pathways in oocyte-somatic cell interactions and gonadal growth and differentiation. In the process, we have produced over 70 transgenic and knockout models to study reproduction in vivo. These models have helped us identify novel and unexplored areas of germ cell biology and translate this work into the fertility clinic.

Silvering of European eel (Anguilla anguilla L.): seasonal changes of morphological and metabolic parameters

Abstract The transformation of yellow eel into silver eel is called 'silvering', and takes place prior to migration. We found the sedentary yellow phase in spring, the migratory silver phase in autumn, while August was a cross-over month. We used principal component analysis (PCA) to characterise the morphological and physiological changes that accompany silvering in the European eel (Anguilla anguilla L.). Silvering is positively related to external parameters such as eye size, internal maturation parameters like GSI, vitellogenine (VIT), and blood-substrates such as phospholipids, Free Fatty Acids (FFA), and cholesterol. The Hepatosomatic Index was not significantly different between yellow and silver groups. In contrast, a significant difference was observed for parameters of body constitution (fat, protein, dry matter) between yellow and silver stages. Furthermore, the process of silvering is accompanied with increased levels of cortisol in autumn, which plays a role in mobilisation of metabolic energy from body stores towards migratory activity and gonadal growth. Based on Principal Component Analysis (PCA) with physiological, morphological and endocrinological parameters, it is concluded that during the process of silvering, several developmental stages can be recognised, with a timeframe of the premigratory sedentary yellow phase from April until July, August is a cross-over month, and the migratory silver phase is found from September until November.

Hypothalamic expression of thyroid hormone-activating and -inactivating enzyme genes in relation to photorefractoriness in birds and mammals

Photorefractoriness is the insensitivity of gonadal development to the stimulatory effects of long photoperiods in birds and to the inhibitory effects of short photoperiods in small mammals. Its molecular mechanism remains unknown. Recently, it has been shown that reciprocal expression of thyroid hormone-activating enzyme [type 2 deiodinase (Dio2)] and -inactivating enzyme [type 3 deiodinase (Dio3)] genes in the mediobasal hypothalamus is critical for photoperiodically induced gonadal growth. Since thyroid hormones are required not only for photoinduction, but also for the induction of photorefractoriness, we examined the expression of these genes in relation to photorefractoriness in birds and mammals. Transfer of birds to long photoperiods induced strong expression of Dio2. This was maintained in tree sparrow when they later became photorefractory, but decreased somewhat in quail. In hamsters, transfer to long photoperiods also induced strong expression of Dio2. High values were not maintained under long photoperiods, and, indeed, expression decreased at the same rate as in animals transferred to short photoperiods. There was no renewed expression of Dio2 associated with testicular growth as animals became refractory to short photoperiods. Expression of Dio3 was high under short photoperiods and low under long photoperiods in all the animals examined, except for the short photoperiod-refractory hamsters. Our present study revealed complex regulation of deiodinase genes in the photoinduction and photorefractory processes in birds and mammals. These gene changes may be involved in the regulation of photorefractoriness, as well as photoinduction.

Dinâmica do desenvolvimento gonadal de Aegla platensis Schmitt (Decapoda, Anomura, Aeglidae)

One way to estimate gonadal development through the reproductive cycle is to observe the growth of the gonads related to the organs used to store energy. The aim of this study was to follow the gonadosomatic and hepatosomatic indexes during annual cycle of Aegla platensis Schmitt, 1942. Adult animals were collected in Taquara, Rio Grande do Sul, Brazil (29°46’S, 50°53’W). Males and females were initially weighed and dissected and had their gonads and hepatopancreas (HP) removed and weighed in order to estimate the Gonadosomatic (GI) and hepatosomatic (HI) indexes. In females, the indexes were also compared to the degree of development of the ovaries. In males the GI showed a peak of gonadal development in the autumn (p < 0.05), just when the HI showed a decrease (p < 0.05). Females showed a rise in the GI at the end of summer and beginning of autumn (p < 0.05). In females, GI values increased as the ovary matured. In A. platensis , for both males and females, the HI never showed values lower than the GI, which may indicate that these aeglids show a different pattern of energy utilization from other decapods, where as gonadal development peaks the HI decreases markedly.

Different Neural Melatonin‐Target Tissues are Critical for Encoding and Retrieving Day Length Information in Siberian Hamsters

Siberian hamsters exhibit several seasonal rhythms in physiology and behaviour, including reproduction, energy balance, body mass, and pelage colouration. Unambiguous long- and short day lengths stimulate and inhibit reproduction, respectively. Whether gonadal growth or regression occurs in an intermediate day length (e.g. 14 h L : 10 h D; 14L), depends on whether the antecedent day lengths were shorter (10L) or longer (16L). Variations in day length are encoded by the duration of nocturnal pineal melatonin secretion, which is decoded at several neural melatonin target tissues to control testicular structure and function. We assessed participation of three such structures in the acquisition and retrieval of day length information. Elimination of melatonin signalling to the nucleus reuniens (NRe), but not to the suprachiasmatic nucleus (SCN) or paraventricular thalamus (PVt), interfered with the acquisition of a long day reproductive response, whereas the obscuring of melatonin signals to the SCN and the NRe, but not to the PVt, interfered with the photoperiod history response. The SCN and NRe contribute in different ways to the melatonin-based system that mediates seasonal rhythms in male reproduction.

The relationship between feed intake and gonad growth of single and stocked green sea urchin ( Strongylocentrotus droebachiensis) in a raceway culture

This study provides a robust relationship between feed intake (FI), gonad growth (GG), and feed conversion ratio (FCR) of cultured adult green sea urchin Strongylocentrotus droebachiensis. Sea urchins (test diameter: ∼ 54 mm and live weight: ∼ 70 g) were collected in the wild and cultured either individually or subjected to one of three stocking densities, i.e. low 2.5 ( N = 36), medium 3.7 ( N = 54), or high 7.3 ( N = 108) kg animal per m 2. Animals were fed a prepared diet in excess for 56 days at 6.5–4.5 °C. The gonad index (GI) more than doubled during the 56 day trial. The final mean values of GI (17–18%), FI (0.3–0.4 g feed per animal per day), and FCR (∼ 3 g feed per g increase in gonad weight) were statistically similar between individual and stocked animals. Based on data from the individually cultured sea urchins, the relationship between daily FI (g feed per animal) and GG (g gonad increase per animal) could be described by the equation: GG = 0.619FI − 0.097 ( R 2 = 0.533, P < 0.001). In conclusion, marketable sizes of green sea urchin perform well in raceways at densities of 7–8 kg animal per m 2 without adverse effects on FI, GG, and FCR.

The effects of stocking density on gonad growth, survival and feed intake of adult green sea urchin ( Strongylocentrotus droebachiensis)

In this study the effects of different stocking densities on survival, gonad growth and feed intake in adult green sea urchin ( Strongylocentrotus droebachiensis) were examined. Two size groups of sea urchins with respective initial mean weight of 45 g (S) and 70 g (L) were used. The experiments were carried out in 755 l plastic tanks divided into chambers by vertical fibreglass lamellae. In the two experiments stocking densities of 6, 12, 14 and 16 kg m − 2 (Exp I) and 3, 6 and 8 kg m − 2 (Exp II) were used. Sea urchins reared individually in compartmentalised raceways were used as controls in both experiments. All groups were fed a formulated moist feed ad libitum for 60 days at 8 °C (± 0.5). Mortality was observed in all groups, except for the control group and the lowest density group of large sea urchins (3 kg m − 2 , L). Both mortality and occurrence of injuries increased significantly with increasing stocking density in both experiments and for both size groups. In the highest density groups mortality was 60% (L) and 80% (S). There was a significant increase in gonad index during the experimental period in both experiments. Increased stocking density had a significantly negative effect on gonad growth in both size groups while feed intake was unaffected. The results show that adult S. droebachiensis can maintain high survival rate and high gonad growth at stocking densities up 6 kg m − 2 in holding facilities of the design used in the present study.

Interval Timer Control of Puberty in Photoinhibited Siberian Hamsters

Puberty, which is markedly delayed in male Siberian hamsters (Phodopus sungorus) born into short day lengths, is controlled by an interval timer regulated by the duration of nocturnal melatonin secretion. Properties of the interval timer were assessed by perturbing normal patterns of melatonin secretion in males gestated and maintained thereafter in 1 of 2 short day lengths, 10 h light/day (10 L) or 12L. Melatonin secretion of short-day hamsters was suppressed by constant light treatment or modified by daily injection of propranolol to mimic nocturnal melatonin durations typical of long-day hamsters. Constant light treatment during weeks 3 to 5 induced early incomplete gonadal growth in 12L but not 10 L hamsters but did not affect late onset of gonadal development indicative of puberty in either photoperiod. Propranolol treatment during postnatal weeks 3 to 5 induced transient growth of the testes and ultimately delayed the timing of puberty by 3 weeks. Similar treatments between weeks 5 and 7 or on alternate weeks for 24 weeks did not affect the interval timer. The first 2 weeks after weaning may constitute a critical period during which the interval timer is highly responsive to photoperiod. Alternatively, the hamsters' photoperiodic history rather than age or developmental stage may be the critical variable. The interpolation of long-day melatonin signals at the time of weaning does not appear to reset the interval timer to its zero position but may reduce timer responsiveness to long-day melatonin signals several weeks later.

REPRODUCTION AND SPAWNING IN CALICO SCALLOPS, ARGOPECTEN GIBBUS, FROM BERMUDA

The gametogenic cycle and breeding season of the calico scallop, Argopecten gibbus was examined in Bermuda using quantitative and qualitative methods. Gonadal index varied seasonally, a rapid increase occurring in the winter months from January to March, and reaching maximum values in March and April. Greatest gonad growth and spawning were associated with low seawater temperature and low food levels. Variations in muscle indices implied a partial reliance on muscle reserves during the early stages of oogenesis. The later stages of ovarian growth (vitellogenesis and oocyte maturation) seemed to show a direct dependence on food supply. Histological analysis indicated the initiation of gamete development in early fall, when cell differentiation was first observed; oocyte ripening took place in late fall and early winter, reflected in increased oocyte diameters and gonadal indices. The lack of spawning activity during the hot summer months was seen histologically by the high proportion of spent cells in the gonads and a reduction in oocyte size, resulting in a minimal gonadal index. Individuals with gonad indices above 2 and mean oocyte diameters exceeding 50 μm were induced to spawn with thermal shocks, exceeding 70% response rate in oocyte release in all trials. The present study extends our limited knowledge of the reproductive cycle in this subtropical scallop while providing a useful index to evaluate spawning readiness in cultured broodstock for routine hatchery purposes.

Variation in nitrogenous compounds and gonad index in fed and starved sea urchins (Paracentrotus lividus) during live storage

Wild-caught Paracentrotus lividus were fed either Ulva lactuca or starved during the post-spawning period of their biological cycle. Growth and the gonad indices were monitored throughout the experimental period in order to determine the relationships between nutritional state and the allocation of resources to body components. No variation in the wet weight of starved or fed urchins occurred but a significantly increased gonadal growth occurred in the fed urchins after 36days and established a direct relationship between food availability and gonad development.Initial mean values of ammonia and nitrate excretion of 46.03±4.28 5mol NH4-N individual−1 h−1 and 0.45±0.04mg NO3 individual−1 h−1, respectively, dropped to 2.55±0.33NH4-N μmol individual−1 h−1 and 0.1±0.02mg NO3 individual−1 h−1 after 5days (p<0.05; one-way ANOVA in each case). Concomitantly, free amino acid concentrations dropped in the gonads and the coelomic fluid. Coelomic fluid TMA concentrations were constant throughout all the conditioning period; however, an increase of the gonad TMA level occurred after 5days to reach a mean of 0.37±0.02μmol TMA g−1 and then remained stable to the end of the experiment (36days).

Development of chronic tests for endocrine active chemicals: Part 1. An extended fish early-life stage test for oestrogenic active chemicals in the fathead minnow ( Pimephales promelas)

An extended early-life stage test (based on OECD test guideline 210) was developed to allow the evaluation of a weak environmental oestrogen, 4- tert-pentyphenol (4TPP), on sexual differentiation and gonadal development. Fathead minnow ( Pimephales promelas) embryos were exposed to three concentrations of 4TPP (56, 180 and 560 μg l −1) in a flow-through system, at 25 ± 1 °C, for <107 days post-hatch (dph). In addition, some embryos were exposed to 180 μg 4TPP l −1 until 30 or 60 dph, after which they were exposed to dilution water only until 107 dph. At 30, 60 and 107 dph fish were evaluated for growth and gonadal development (via histology), and at 107 dph fish were also evaluated for secondary sexual characteristics (SSC), gonadosomatic index (GSI) and plasma vitellogenin (VTG). There were no effects of 4TPP on hatching success or survival, however, there was a delay in the time taken for embryos to hatch (560 μg 4TPP l −1). No treatment-related effects were observed on fish growth, with the exception of at 107 dph when the condition factor in female fish was reduced in all 4TPP continuous exposure treatments. Plasma VTG was only elevated in female fish exposed to 180 μg 4TPP l −1 and inhibition of gonadal growth (GSI) occurred only in females exposed to 560 μg 4TPP l −1. Histological examination of the gonads revealed delays and disruption in male sexual differentiation and development (180 μg 4TPP l −1) and no testicular tissue was observed in any fish exposed to 560 μg 4TPP l −1. Mixed gonads (predominately testes with a scattering of primary oocytes) were present in fish exposed to all doses of 180 μg 4TPP l −1 at 107 dph. Feminisation of the reproductive ducts (formation of an ovarian like cavity) occurred in the testis of all males exposed to 180 μg l −1, regardless of length of 4TPP exposure. Results indicate that the period of 30–60 dph appears to be the sensitive window for disruption of formation of the reproductive duct and this effect is not reversible when the fish are transferred to dilution water. The data also show that this integrative test is suitable for the detection of a weak environmental oestrogen and comparisons of these results with that of a fish full life-cycle, in medaka, indicate that this test could be a suitable surrogate for a fish full life-cycle.

Effects of temperature and season on gonad growth and feed intake in the green sea urchin ( Strongylocentrotus droebachiensis)

The effects of water temperature and season on feed intake and gonad growth of green sea urchin Strongylocentrotus droebachiensis were evaluated. Animals were tested at six temperatures (4, 6, 8, 10, 12, and 14 °C) in summer (July–September) and in winter (November–January). Sea urchins (64.5 ± 3.4 g mean wet body weight ± S.D.) were held individually in square chambers and fed ad libitum a formulated moist feed. Gonad index (GI), feed intake (FI), and feed conversion ratios (FCR) were measured. There was a significant increase in GI for all treatments during the summer trial, and sea urchins held at 6 °C had a significantly larger GI compared to those held at 4 °C ( P < 0.05). There was no significant difference in GI between sea urchins held at 10, 12 and 14 °C, and they had a significantly higher GI compared to the lower temperature groups. In the winter trial sea urchins held at 8 °C displayed a significant higher GI compared with the other temperatures. There was a significant and linear increase in FI with increasing temperature both during summer and winter. Thus, FI in the summer (S) and winter (W) trials increased from initial 0.34 (S) and 0.26 (W) (g/urchin per day) at 4 °C, to 0.71 (S) and 0.93 (W) (g/urchin per day) at 14 °C. In summer, sea urchins held at 12 °C had a significantly lower FCR (3.3) compared to animals held at 8 °C (FCR = 4.0). The situation was reversed in winter, where sea urchins displayed the lower FCR (3.7) at 8 °C than those held at 12 °C (FCR = 6.0). Overall, our findings suggest that optimum gonad growth of adult green sea urchins is achieved at higher temperatures in summer than in winter.

Rapid inhibition of female sexual behavior by gonadotropin-inhibitory hormone (GnIH)

Gonadotropin-releasing hormone (GnRH) is largely responsible for the initiation of sexual behaviors; one form of GnRH activates a physiological cascade causing gonadal growth and gonadal steroid feedback to the brain, and another form is thought to act as a neurotransmitter to enhance sexual receptivity. In contrast to GnRH, gonadotropin-inhibitory hormone (GnIH) inhibits gonadotropin release. The distribution of GnIH in the avian brain suggests that it has not only hypophysiotropic actions but also unknown behavioral actions. GnIH fibers are present in the median eminence (ME) and are in apparent contact with chicken GnRH (cGnRH)-I and -II neurons and fibers. In birds, cGnRH-I regulates pituitary gonadotropin release, whereas cGnRH-II enhances copulation solicitation in estradiol-primed females exposed to male song. In the present study, we determined the effects of GnIH administered centrally to female white-crowned sparrows. A physiological dose of GnIH reduced circulating LH and inhibited copulation solicitation, without affecting locomotor activity. Using rhodaminated GnIH, putative GnIH binding sites were seen in the ME close to GnRH-I fiber terminals and in the midbrain on or close to GnRH-II neurons. These data demonstrate direct effects of GnIH upon reproductive physiology and behavior, possibly via separate actions on two forms of GnRH.

Production of interploid triploids by 4n x 2n blunt snout bream (Megalobrama amblycephala. Yih) and their first performance data

Positive and negative interploid triploids of blunt snout bream (Megalobrama amblycephala) were produced by reciprocal crossing autotetraploids with diploids. Fertilization and hatching rate of negative interploid triploid, 2n♀× 4n♂, at different reproductive ages was similar to that of control, but higher than that of positive interploid triploid, 4n♀× 2n♂. Additionally, the development rate of embryos of the positive interploid triploid, 4n♀× 2n♂, was slower than that of control and the negative interploid triploid, 2n♀× 4n♂. Gonad growth of the positive and negative interploid 3n was significantly (P<0.01) affected by parents, and spawning could not be induced both in females and males at the 2+ age. The negative interploid 3n (2n♀× 4n♂) had a significantly higher survival rate than the positive interploid 3n (4n♀× 2n♂), but close to the level of the control (P<0.05). The daily growth rate of the negative interploid 3n was similar to that of the good breed ‘Pujiang No. 1’ blunt snout bream (2n) during the early life stages.

The reproductive biology of a new species of sea cucumber, Holothuria (Mertensiothuria) arenacava in a Kenyan marine protected area: the possible role of light and temperature on gametogenesis and spawning

The sea cucumber Holothuria arenacava was discovered in the Mombasa marine reserve in 1997 and described by Samyn et al. (2001). The reproductive biology of this holothurian was investigated in order to (1) characterize the reproductive pattern, (2) examine the relationship among environmental parameters including temperature, light and lunar period, and (3) examine the relationship between the reproductive pattern and feeding of this new species. The gonad index method and microscopic examination of gonads was used to analyze samples collected for a period of 13 months. H. arenacava displayed an annual reproductive cycle with gametogenesis commencing in July during the south-east monsoons, when temperature and light intensity are lowest along the Kenyan coast. Gonad growth peaked in February–March at the end of the north-east monsoons when temperatures and light reach their annual maxima along the Kenyan coast. The higher correlation between light intensity and gonad growth (r=93) than temperature (r=0.71), coupled with the fact that temperatures continued to drop for a month after gametogenesis had already commenced, suggests that light intensity and not temperature is the cue for the onset of gametogenesis in this species. Spawning was synchronized between females and males and occurred during a short period between March and May (inter-monsoonal period) when both temperature and light intensity decrease along the Kenyan coast. Male and female gonad indices showed significant variation with lunar day and no lunar periodicity was observed in this sea cucumber. The sex ratio of the population of H. arenacava was skewed towards significantly more females than males, and females were significantly larger and had larger gonads and gonad indices than males. These life history strategies including spawning during a short discrete period, more and larger females that have larger gonads (i.e., typically more fecund), and spawning just prior to the peak in phytoplankton concentrations, a time that is probably more favorable for larval development, may serve to increase the reproductive success of this sea cucumber.

PCB congener-specific disruption of reproductive neuroendocrine function in Atlantic croaker

Exposure of Atlantic croaker to Aroclor 1254 has been shown to impair reproductive neuroendocrine function in this species. In addition, we have identified hypothalamic tryptophan hydroxylase (TPH), the rate-limiting enzyme in serotonin synthesis, as a target of PCB neuroendocrine toxicity. A previous study in rats has implicated di-ortho-substituted non-coplanar PCB congeners in the inhibition of a similar enzyme, tyrosine hydroxylase, which is the rate-limiting enzyme in dopamine synthesis. Therefore, the present study was designed to investigate whether di-ortho-substituted congeners (PCB 47, PCB 153) or a coplanar congener (PCB 77) present in Aroclor 1254 could be responsible for the reproductive impairment observed in croaker exposed to the PCB mixture. Fish were exposed to PCB 47 and PCB 153 in the diet (0, 0.2 and 1.0 mg/kg body weight/day) for 30 days and to PCB 77 (0.01 and 0.1 mg/kg body weight/day) for 15 days. Neither PCB 47 nor PCB 153 altered hypothalamic TPH activity or gonadal growth at doses similar to the effective doses of the Aroclor 1254 mixture. Therefore, these ortho-substituted PCB congeners known to be neurotoxic in mammalian systems are unlikely to contribute to Aroclor 1254-induced reproductive neuroendocrine disruption in croaker. In contrast, PCB 77 significantly inhibited hypothalamic TPH activity and gonadal growth at doses much lower than the effective doses of Aroclor 1254. The results provide the first evidence for PCB congener-specific disruption of reproductive neuroendocrine function in a vertebrate species.