Lipid and fatty acid content in wild white seabream (Diplodus sargus) broodstock at different stages of the reproductive cycle

The lipid and fatty acid content of the gonads, liver and muscle of wild white seabream males and females was studied at different stages of the reproductive cycle. Samples were taken from mature white seabream at pre-spawning (November), mid-spawning (March) and post-spawning (June) stages. The results showed that lipid accumulates in gonads and muscle from November to March. The gonadosomatic index (GSI) was also increased during this period. Male gonads showed a greater increase in polar lipid (PL) than neutral (NL), while female gonads displayed the reverse. The increase in both neutral and polar lipid was higher in the muscle of males than in females. In the same period, male livers showed no changes either in lipid content or the hepatosomatic index (HSI), while female livers registered an increase in both lipid content and HSI. Between March and June, in both males and females, total, neutral and polar lipid decreased sharply in the gonads and muscle. Muscular lipid content reduction was more pronounced in males than females. On the other hand, the lipid content of the liver in males and females remained relatively constant. In general terms, the amounts of major fatty acids (16:0, 18:1n-9, 20:5n-3 and 22:6n-3) in gonadal and muscular polar and neutral lipid in both males and females increased from November to March and declined thereafter. Variations of the liver fatty acid content were less extreme. In the period from mid-spawning to post-spawning, the presence of 20:4n-6 in polar and neutral lipid increased to a notable extent in all organs studied.     

Lipid dynamics in the common torpedo, Torpedo torpedo, from the south eastern Mediterranean

Liver stores the major part of lipids in both mature and immature Torpedo torpedo of both sexes. Fluctuations in the lipid contents of liver, muscles and gonads of immature fish followed the relative change in food intake throughout the year. Hepatic and muscular lipids in mature females diminished before ovulation and were intensively consumed in the last stages of gestation (in pregnant females). After parturition, the recovery of the lipid stores was very rapid due to intensive food uptake. Storing of hepatic lipids in mature males started a little before gonadal maturation and reached a maximum in January and February while gonadal lipids decreased in the same period. Gonadal lipid for both sexes fluctuated in parallel to fluctuations in the GSI. Water content showed significant inverse correlation with lipid content in both liver and gonad tissues, but no significant correlation was recorded in the muscle tissues.     

Variation in biochemical composition during gonad maturation of the tropical abalone Haliotis varia Linnaeus 1758 (Vetigastropoda: Haliotidae)

Biochemical changes in the body components during gonad maturation of the tropical abalone Haliotis varia were investigated using wild collected specimens from the Gulf of Mannar, on the southeast coast of India. The gonadosomatic index (GSI) and the hepatosomatic index (HSI) showed negative correlations throughout the study period as well as during the progression of gonad maturation stages. The highest GSI for both the sexes were in the ripe stages followed by late maturing stages. The HSI ranged from 2.97 to 6.71 in females, and 3.55 to 5.09 in males. Among the biochemical components analysed, lipid and carbohydrate contents showed significant variations in the different tissues of H. varia during the progress of gonad maturation. The highest protein content was in the foot muscle and the lowest was in the digestive gland. Total lipids in the ovary were always higher compared with that of the testis and the values ranged from 12.60 to 26.49%, registering the highest value in the ripe ovary. Gonad carbohydrate content was lower when the lipid content was higher, suggesting the conversion of carbohydrate to lipids. The present study demonstrates the role of nutrient translocation between body parts as an essential part of the reproductive physiology of abalone.     

Seasonal fluctuation in lipid and cholesterol content of ovary, liver and blood serum in relation to annual sexual cycle in Heteropneustes fossilis (Bloch).

Seasonal fluctuation in lipid content of ovary and liver and cholesterol content of ovary, liver and serum in relation to annual reproductive cycle in H. fossilis has been worked out. Reduction in lipid content of liver was associated with decrease in hepatosomatic index (HSI) in prespawning and spawning phases. But there was an obvious increase in the lipid level of ovary in the above phases which coincided with enhanced gonadosomatic index (GSI) records. Serum and ovary showed a subsidence in their cholesterol contents in prespawning followed by increased level during spawning period. Substraction in liver cholesterol started in prespawning and continued till spawning phase and thereafter regained upward trend. Lipid and cholesterol levels in all organs studied along with GSI and HSI returned to initial values by the end of postspawning stage. Administration of clomid, sexovid, PGE1 and PGF2 alpha for a week did not induce any change in HSI, GSI, lipid and cholesterol values of liver and serum. However, these drugs were effective in suppressing the ovarian cholesterol within a week. The above drugs seem to affect cholesterol level indirectly since they trigger gonadotrophin secretion which in turn probably accelerated cholesterol utilization in ovary for increased steroid hormone output.     

Sex steroids,gonadal histology and biological indices of fall and spring Caspian lamprey (<Emphasis Type="Italic">Caspiomyzon wagneri</Emphasis>) spawning migrants in the Shirud River,Southern Caspian Sea

This study investigates sex steroids, gonadal histology and some biological indices of fall and spring spawning migrants of Caspian lamprey Caspiomyzon wagneri (Kessler, 1870). Blood and gonad samples were collected from 15 migrants during fall and spring. Serum sex steroid levels including testosterone (T), 17β-estradiol (E₂) and progesterone (P) were determined with ELISA and gonadal development was studied using conventional histological methods. Our results showed serum E₂ level in females were similar in the two seasons but in males, fall migrants had higher serum E₂ concentrations. No differences were found in T levels in fall and spring migrants. Serum P concentration in fall migrant males were significantly higher than spring migrant males while spring migrant females had higher serum P levels compare to fall migrant females. Gonads in both fall and spring migrants were in the final stage of maturity. Fall and spring migrant males had similar HSI and GSI; fall migratory female had significantly higher HSI and GSI. Sex ratios were close to 1:1 in both seasons. There was a significant relationship between fecundity and length in both seasons. Comparison of fecundity and egg diameter between fall and spring seasons showed no significant difference. These results indicate that both fall and spring migrants Caspian lamprey were ready for spawning. Further studies are needed to clarify when spawning occurs in Caspian lamprey.     

日本鳗鲡雌鳗卵巢发育期间肌肉脂肪酸的组成及消耗

研究采用3种不同的处理方式(I&GD、I&nGD和A&nGD)对雌鳗处理后,进行了生物学相关参数、肌肉脂肪酸组成和含量变化测定分析.研究结果表明,日本鳗鲡在性腺发育期间,体重一直呈一个下降的趋势,直到产卵前,才显著高于野生海鳗.该现象被称为水合反应.实验结束时,3个实验组的脂肪总量均有不同程度的下降,其中,I&GD组下降最多,占总脂肪的66.55%;其次是A&nGD组,占总脂肪的43.76%;下降最少的是I&nGD组,占总脂肪的34.68%.研究对日本鳗鲡的肌肉共测出了17种脂肪酸,SFA 7种、MUFA 2种、PUFA 8种.其中,MUFA虽然只有2种,但在脂肪酸总量中占的百分比却较高达38.02%,而且它们的消耗与性腺发育和基础代谢有关,与雌鳗的游泳耗能无关.在8种PUFA中,AA的变化很特殊.实验期间,它在日本鳗鲡肌肉内是一个积累和消耗的动态过程.而且,积累程度与雌鳗的游动有关,游动越多,积累越多.EPA虽然能被检出,但量很低,而且各组间的变化无明显规律.DHA在日本鳗鲡肌肉中的含量达到123.91 mg/g干肌肉,占总脂肪的32.52%.卵巢发育所消耗的量也很多,I&GD组在卵巢发育结束后,下降到10.59 mg/g十肌肉.相关性分析发现.虽然总脂肪酸、PUFA、DHA和EPA与GSI间均存在一定程度的负相关性,但关系最密切的是DHA,其r=-0.952(P<0.01,n=5),关系最小的是EPA,其r=-0.882(P<0.05,n=5).因此分析认为DHA是日本鳗鲡性腺发育所需的最主要的一种脂肪酸.对能量分布进行综合分析后认为,日本鳗鲡在人工诱导性腺发育期间,基础代谢所需的脂肪量(LBM)占总脂肪量的34.68%,性腺发育所需脂肪量(LGD)占总脂肪量的32.49%,运动耗能所需脂肪量(LM)占总脂肪量的9.79%.因此认为,日本鳗鲡在不摄食的情况下,肌肉中的脂肪不仅能提供性腺发育所需的营养物质,而且还能满足洄游2000海里到达产卵场所需的能量.     

饲料中不同EPA和DHA含量对黄鳝脂类代谢、生长及繁殖性能的影响

为研究EPA和DHA对黄鳝脂类代谢、生长及繁殖性能的影响, 用添加有EPA和DHA比例相同(EPA/DHA=0.35)但水平不同(EPA和DHA总量分别为0.00%、0.35%、0.70%)的3种等氮等脂肪饲料, 在常温(2230 ℃)下, 分别喂养平均体重为(21.710.54) g的黄鳝7周, 分析黄鳝脂类代谢和生长性能, 然后每组取15尾继续养殖至性腺发育成熟用于繁殖性能分析。结果表明:在饲料中添加0.70%的EPA和DHA 能促进黄鳝生长, 显著提高黄鳝的特定生长率(SGR)及肌肉粗蛋白含量, 降低肝体指数(HSI)及肌肉、肝脏中的粗脂肪含量(P0.05), 显著提高亲鳝的性体指数(GSI)、产卵量、孵化率、幼苗的存活指数(SAI)(P0.05)。添加0.35%的EPA和DHA能显著降低肝脏中粗脂肪含量(P0.05)。综合分析表明:EPA和DHA能促进黄鳝的脂类代谢, 显著提高其生长及繁殖性能; 饲料中添加0.70%的EPA和DHA较为适宜。       

低盐度海水和淡水对中华绒螯蟹性腺发育及交配行为的影响

研究了低盐度海水(盐度为15)和淡水(盐度为0)对中华绒螯蟹(Eriocheir sinensis,以下简称河蟹)性腺发育及交配行为的影响,并比较了河蟹交配和产卵前后的性腺指数及肝胰腺指数的变化。实验分为4组,分别为低盐度海水雌蟹组、淡水雌蟹组、低盐度海水雄蟹组和淡水雄蟹组。结果表明,(1)各组河蟹的成活率均在80%左右,无显著差异(P>0.05);(2)实验第15天、30天和45天时,低盐度海水雌蟹组的卵巢指数显著高于淡水雌蟹组(P<0.05),低盐度海水雄蟹组的性腺指数也略高于淡水雄蟹组,但差异不显著(P>0.05);(3)实验第30天时,低盐度海水雌蟹组的肝胰腺指数显著低于淡水雌蟹组(P<0.05),其余采样时间两组雌体间或两组雄体间的肝胰腺指数差异不显著(P>0.05),实验期间,两组雌体的肝胰腺指数均显著下降(P<0.05);(4)实验第45天,低盐度海水雌蟹组和雄蟹组实验个体全部能够交配,有66.7%的低盐度海水雌蟹组的个体交配后2 d内产卵,淡水雄蟹组有部分个体在低盐度海水中有发情行为;(5)低盐度海水组,雌蟹产卵后和雄蟹交配后的性腺指数均显著下降(P<0.05),但肝胰腺指数下降不显著(P>0.05)。     

Lipid and fatty acid composition of female gilthead seabream during their reproductive cycle: effects of a diet lacking n-3 HUFA

In female sea bream Sparus aurata fed a control diet (C), ovarian levels of neutral lipids (NL) and polar lipids (PL) remained constant between November and March, while a decrease in NL content was observed in liver and muscle. In the same period, liver PL content increased, while no changes were observed in muscle. Between March and June ovarian NL and PL showed a strong decrease, while NL remained constant in liver and muscle. When fish were fed a diet lacking in n-3 highly unsaturated fatty acids, n-3 HUFA (D), the pattern observed was similar to that found in the fish fed diet C, with the exception of liver NL, which increased between March and June. In general, the changes in fatty acid content, in both groups of fish, were highly influenced by the diet given to the broodstock, although these effects were greater on ovarian NL and PL than on liver and muscle lipids. Despite the fact that gilthead seabream females continue feeding during the spawning season, they probably make use of their liver and muscle reserves during the gonadal maturation process. Furthermore, the fatty acid composition of the broodstock diet was reflected in the body composition, especially in the ovaries.     

Effects of dietary lipid source on reproductive performance and tissue lipid levels of Nile tilapia Oreochromis niloticus (Linnaeus) broodstock

Nile tilapia were fed diets supplemented with one of the following lipid sources at 5% level: cod liver oil, corn oil, soybean oil, a coconut oil-based cooking oil or a combination of cod liver oil and corn oil (1 : 1). The control diet had no lipid supplement and tad fish meal as a sole protein source. A diet with soybean meal as a protein source was also tested. The number of females that spawned, spawning frequency, number of fry per spawning, and total fry production were increased at varying degrees by the supplemental lipid sources except for the cod liver oil. Fish fed the soybean oil diet tad the best overall reproductive performance over a 24-week period. Fish fed the cod liver oil diet had the highest weight gain but the poorest reproductive performance. The suplemental lipids significantly increased crude fat levels in the liver and ovaries. Both males and females Ld the cod liver oil diet had the highest levels of fat in the liver and muscle. The ratio of total n-6/n-3 fatty acid in the liver, ovaries and testes was influenced by the supplemental lipid sources. It was highest in fish fed either the soybean oil diet, the corn oil diet, or the soybean meal diet and lowest in fish fed the control diet or the cod liver oil diet.     

Biochemical composition of the Atlantic bonito Sarda sarda from the Aegean Sea (eastern Mediterranean Sea) in different stages of sexual maturity

The content (% wet mass) in water, ash, lipid, crude protein, DNA and RNA of different tissues was determined during sexual maturation of bonitos Sarda sarda from the Aegean Sea. A total of 220 specimens were collected in the following stages of sexual maturity: immature, resting, developing, mature, spawning and spent. Highest lipid levels in the white muscle, red muscle and liver were measured in immature specimens, while lowest levels were found in spawning bonitos. The gradual percentage of lipid reduction from immature to spawning bonitos was relatively higher in the liver (females 71·2% and males 64·4%) than in the white (females 59·2% and males 53·5%) and red (females 62·1% and males 51·7%) muscle. Lipid levels in the gonads increased gradually from the immature to spawning stage. The decrease of lipid in the somatic tissues was more intense in females than in males, and gonadal lipid content was higher in females than in males. There was a strong reverse correlation between water and lipid percentage in all tissues. Protein content decreased significantly only in spawning bonitos. The percentage of protein reduction from immature to spawning stage was relatively higher in males than in females in both white (females 3·4% and males 4·6%) and red (females 4·6% and males 5·1%) muscles. Protein content in the liver was significantly lower than in the other tissues, being highest in mature females. Gonadal protein content in females increased with maturation and decreased after spawning. The content in ash exhibited considerable stability. The RNA:DNA ratio exhibited a similar pattern of variation in both muscles. The RNA:DNA ratio increased during gonadal development gradually from the developing to spent stage. It was concluded that in S. sarda during gonadal development, there was an increase in gonadal lipid accompanied by a decrease in somatic tissue lipid reserves. Thus, reproductive inactive bonitos have more lipid in their edible part and a higher nutritional value than active ones.     

Plasma sex steroids and gonadosomatic index variations during ovarian development of female wild yellowfin seabream (Acanthopagrus latus)

The yellowfin seabream (Acanthopagrus latus) has a good potential for mariculture in Iran, so studies on various aspects of its culture has been carried out. In this study, the characteristic of reproduction in this species was investigated. The involvement of steroid hormones in the development of gonads was assayed by sampling blood and gonad tissue in 85 females of A. latus in fish caught from the Musa Creek, north-west Persian Gulf from October 2010 to May 2011. Gonadosomatic index (GSI) and hepatosomatic index (HSI) were recorded. Developmental stages were associated with changes in sex steroids, GSI and HSI. GSI and HSI began to increase in November (immature stage) and reached the highest value in March (ripe stage), decreasing sharply in April (spent stage). Plasma values of 17β-estradiol (E2) levels reached their highest levels in spawning females in March and then decreased in April. Progesterone levels were low through ovarian development, reached a maximum simultaneously with testosterone in February (mature stage) and then decreased in March (ripe stage). The seasonal changes observed in plasma steroid levels and GSI reflected the pattern of oocyte development and the spawning behavior of yellowfin seabream and were typical of the patterns described in most multiple spawners studied to date.     

雅鲁藏布江黑斑原鮡繁殖生物学研究

对2004-2006年采集于雅鲁藏布江拉萨河的190尾黑斑原鮡进行了繁殖生物学研究。雄性最小性成熟(精巢Ⅳ期)个体体长141.7mm,体重45.2g,性体指数1.09%,雌性最小性成熟(卵巢Ⅳ期)个体体长146.8mm,体重66.7g性体指数11.52%,相应年龄均为5龄。初次性成熟年龄(L50):♂,170.1mm相应年龄为7龄;♀,150.2mm,相应年龄5龄。通过组织切片法和GSI的周年变化分析,繁殖时间集中在5-6月,每年繁殖一次,繁殖之后的6-8月卵巢从Ⅵ期回复到Ⅲ期,9月卵巢发育到Ⅳ期越冬。卵径频率分布显示,卵巢发育类型为分批同步型,卵巢中至少存在2批卵径,每年成熟一批卵并同时产出,产卵类型为完全同步产卵。卵黏性,成熟卵卵径在2.04-3.37mm之间,平均(2.83±0.16)mm。对19尾产卵前夕(体长为151.0-210.0mm)的标本进行统计,其绝对繁殖力范围在525-2058粒之间,平均为(1244±346)粒,相对繁殖力为(14.7±5.8)粒/g。绝对繁殖力与体长呈直线正相关,表达式为F=13.624L-1187。       

Sex differences in the energetic content of reproductive tissues in the Blackeye Goby,Rhinogobiops nicholsii

Differential energetic investment in reproduction between the sexes has been a driving a force of life history theory and sexual selection. However, reproductive costs between the sexes have often been based on morphology, such as gonad mass and gonadosomatic indices (GSI), and few have directly measured the energy content of gonadal tissues in relation to GSI. Using the blackeye goby, Rhinogobiops nicholsii, we measured the energetic content of whole gonadal tissues, specifically testes, ovaries and associated reproductive tissues using oxygen bomb calorimetry. The energy content per gram unit of gonadal tissues was generally predictive of GSI, indicating that GSI is a reasonable measure of energetic costs. Interestingly, although females had greater gonadal mass, GSI and energy content per gram than males, the sex difference in energy content per mass unit was only 13 %, suggesting that gross indices such as gonadal mass or GSI may overestimate energetic costs where instead the cost difference in a unit gram of gonadal tissues between the sexes is smaller than often predicted. This study also demonstrates that although the cost of ovaries is greater than testes, males’ investment in reproductive tissue can be considerable, which is consistent with the often inflated reproductive success for males in haremic mating systems.     

Morphological and gonadal assessments from historical collections of Bluenose Shiners Pteronotropis welaka

Management and conservation have begun to rely on supplemental information to make appropriate decisions. In organisms with little available information, preserved specimens may be particularly important for researchers to continue their role in the management process. Bluenose Shiners are a minnow species that can benefit from such analyses as they are of conservation concern across their native range in the Southeastern United States. To supplement conservation, the objectives were to: (a) quantify sexual dimorphism through a comprehensive morphological analysis, (b) approximate peak spawning condition of males and females through GSI measurements over the anticipated spawning season, and (c) utilize female gonad histology to refine conclusions regarding spawning condition from GSI. Historical collections of Bluenose Shiners obtained from the Tulane University Biodiversity Research Institute were used to conduct morphological and gonadal analyses. While males expressed all morphometrics to a greater degree, male dorsal and anal fin length appears to be the most distinguished characteristic beginning at a total length of approximately 45 mm. GSI displayed peaks in the samples from April 21, 1957 and June 1, 1968; female GSI from Black Creek, MS in April, May, and June of 1986 suggested a peak in late May. Gonad histology showed a progression towards final oocyte maturation through May to early June, via relative prevalence of stage IV and absence of stage I oocytes. This information can be used to supplement future morphometric analyses and reproductive studies performed on Bluenose Shiners or other fish species.     

Seasonal patterns of growth, lipid deposition and lipid depletion in anadromous Arctic charr

Seasonal patterns of growth, lipid deposition and lipid depletion were studied in anadromous Arctic charr from a north Norwegian population. Samples were collected in late May when fish were migrating between fresh water and the sea, and in mid-July when the fish re-entered fresh water. A sample of maturing fish captured in mid-July was held in captivity until late September to assess lipid mobilization linked to the final stages of maturation. The fish increased substantially in weight during their 40–50-day summer residence in sea water (immatures from c . 300 to 600 g; maturing fish from c . 500 to 800 g), and body lipid stores were increased approximately fivefold. The carcass (head, skeleton and skin) was the major lipid depot, accounting for c . 50% of the total lipid content when the fish re-entered fresh water from the sea. The muscle of the ascending charr contained 35–40% of the body lipids, whereas the gut and liver each held 4–5%. Body lipid decreased 30–40% during the period between the re-entry of the fish to fresh water and spawning; although lipids were depleted from all depots the carcass and muscle were quantitatively the most important. By the time of spawning, the gonads of the females held almost 25% of the body lipid, whereas in the males the gonads accounted for <3% of the total lipids. Females lost c . 80% of their body lipid during spawning and overwintering, and, consequently, the lipid depots were severely depleted by the early spring. By contrast, lipid depletion in the males amounted to 50–55% of total lipid in the same period. These data suggest that the combination of spawning and overwintering in fresh water imposes a greater load on the females than on the males. It may be that the severity of the depletion prevents females from spawning in successive years.     

Interspecific differences in growth of somatic and reproductive tissues during the breeding season in Menidia menidia and M. beryllina

The annual atherinid fishes, Menidia menidia and M. beryllina , are extremely similar morphologically, but appear to differ in their energetics and life histories. They emerge from winter in relatively emaciated condition. Menidia menidia males and females showed little change in carcass weight but significant increases in gonad weight in March and April prior to spawning in May. Female liver weight increased in March and remained high. Thus, this species had reached its reproductive size in the autumn and allocated its energy to gonadal growth during the spring. Menidia beryllina showed no significant increases in weight until early May, when carcass, liver and gonad all increased simultaneously, a pattern very different from its congener. The later spawning of M. beryllina is probably due both to its need for carcass growth in spring prior to spawning and to its apparent requirement for warmer water for growth. Females of both species invested more into liver and gonad than did males. Maximum gonadosomatic index was about twice as large for M. menidia males as for M. beryllina males, but the index was similar for females of both species.     

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).     

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.     

Gonadal development and associated changes in liver size and sexual steroids during the reproductive cycle of captive male and female Atlantic cod (Gadus morhua L.)

Gametogenesis in female and male Atlantic cod (Gadus morhua L.) was investigated by sampling blood plasma and gonadal tissue from 19 to 33-month-old fish. The reproductive cycles of both female and male Atlantic cod are characterized by distinct annual variations in gonadal size and developmental stage and these are associated with changes in sex steroids and liver size. I(H) did not change during early gonadal development, but both spent females and males had lower I(H) than late maturing females and spermiating males, respectively. In females I(G) was correlated to plasma E2 levels and they were highest in spawning females. The lowest levels during the reproductive cycle were observed in spent females. Plasma T levels were low throughout ovarian development, and were at a minimum in spent females. 11-ketotestosterone in plasma of males increased rapidly during spermiation, while T increased at earlier testicular stages and reached maximum during spermiation. High plasma levels of steroids in male and female cod during spawning serve to promote further development and growth of less advanced stages of germ cells.