Seasonal changes in hepatosomatic index,gonadosomatic index and plasma estradiol‐17β level in captively reared female rabbit fish (Siganus guttatus)

The seasonal changes in hepatosomatic index (HSI), gonadosomatic index (GSI) and plasma estradiol‐17β (E₂) level in female rabbit fish (Siganus guttatus) were investigated. The relationship between plasma E₂ levels with these indices and ovarian growth was also evaluated. Each month, at least 10 female broodfish were sacrificed to collect liver, ovary and blood for HSI, GSI and plasma E₂, respectively. GSI and HSI were calculated as percentage (%) of relative weight of gonad and liver to total body weight, respectively. Plasma E₂ level was measured using enzyme‐linked immunosorbent assay method (ELISA). Ovaries were cut and stained for histological observation. The results included seasonal changes in plasma E₂ levels, stages of ovarian development, GSI and HSI. The highest level of E₂ was observed in June (1,445.62 pg/ml) and during vitellogenesis (2,305 pg/ml). GSI and HSI values significant fluctuated monthly. The highest HSI and GSI were 1.72% in May and 3.58% in June, respectively. The pattern of plasma E₂ levels showed a relationship with GSI and different stages of ovarian development. HSI was associated with ovarian stages. During vitellogenesis, the highest value (1.9%) of HSI was observed. Histological sections showed that rabbit fish is a multiple spawner. These results contribute to further understanding of female rabbit fish reproductive biology in captivity. Important reproductive parameters such as HSI, GSI and E₂ can be used to indicate maturation status of this fish species.     

Further evidences of deep-sea recruitment of Aristeus antennatus (Crustacea: Decapoda) and its role in the population renewal on the exploited bottoms of the Mediterranean

Data were collected during four trawl surveys (April, May, June and September 2006) in the north-western Ionian Sea (Eastern Mediterranean) with the aim of investigating the recruitment and population structure of Aristeus antennatus and evaluating whether population processes on bottoms deeper than 800 m could have a role to the renewal of the exploited population on fishing grounds, above 800 m. Samples were taken randomly between 400 and 1200 m using a professional fishing vessel equipped with an experimental otter trawl net, with 20 mm stretched mesh size in the cod-end. No variation in density index was shown across the whole depth range while the negative trend of biomass index with depth was due to the increasing proportion of small individuals and males. The recruitment was observed on a wide depth range with an increasing frequency of occurrence at greatest depths. It seems to occur as a discrete phenomenon. A significant bigger-shallower phenomenon was detected in the female population indicating upwards displacement from virgin grounds to fishing ones. The exploited population mostly consists of large females. Mating and reproduction also occur in deep waters. The contribution to the renewal of the fishing population by the virgin one seems to be mostly due to the recruitment on unexploited deep areas and displacement of individuals from these areas to fishing ones. The deep waters act as a refuge area mostly for the recruitment of A. antennatus and, to lesser extent, for spawners. On the basis of all these results the authors discuss the optimum exploitation conditions often detected for this shrimp throughout the Mediterranean highlighting the fact that, since the exploited population mostly consists of reproductive females, conditions of “recruitment overfishing” might occur in A. antennatus contrary to other Mediterranean demersal resources.     

Migration and movement profiles of a potadromous fish (Brachymystax lenok Pallas 1773) in a highly connected river system (Mongolia)

Understanding a species’ spatial and temporal movements along with the way these shift under extreme environmental conditions is vital for developing scientifically sound conservation and management strategies. The aim of this research was to describe and quantify the seasonal migration patterns and fine‐scale movement profiles of Brachymystax lenok, a threatened, potadromous salmonid that inhabits the highly connected, boreal river basins of Siberia and northern Asia. During this study 21 mature individuals were monitored over a 15 month period in the upper Eroo River basin, Mongolia, using passive acoustic telemetry. Mean (±SD) B. lenok home ranges were 19.1 ± 15.1 km (median = 11.5 km), with maximum longitudinal movements detected > 45.3 km. Two periods of increased movements were identified; the first in late summer/early autumn when 10 B. lenok moved into deeper, overwintering pools, with the second period occurring in late spring and early summer when nine B. lenok were detected entering the surrounding tributaries. Diel activity and depth typically increased during daylight hours followed by decreased activity or resting periods in shallower river sections at night. These results highlight the need to maintain a high level of river connectivity and adequate fishing season closures by implementing and enforcing an expansive spatiotemporal management plan that can better protect and recover the Mongolian B. lenok populations. Such measures should be transferable to other threatened, potadromous fish species residing throughout the world's boreal river basins.     

Biofloc technology in intensive broodstock farming of the pink shrimp Farfantepenaeus duorarum: spawning performance,biochemical composition and fatty acid profile of eggs

A 45‐day trial was performed to evaluate the effect of biofloc technology (BFT) with or without fresh food (FF) supplementation during pre‐maturation period on Farfantepenaeus duorarum spawning performance, biochemical composition and fatty acid profile of eggs as compared with conventional clear‐water system (CW+FF). Females raised in biofloc and that received FF supplementation (FLOC+FF) achieved better spawning performance in terms of number of eggs per spawn (49 × 10³), number of eggs per spawn per g of spawner's body weight (2.1 × 10³) and egg size (~275 μm) as compared with CW+FF (23 × 10³, 1.1 × 10³ and 263 μm respectively), but both treatments did not vary from FLOC (P > 0.05). High spawning activity was also observed in biofloc system as compared with clear‐water system as shown in number of spawns per ablated female (2.2–3.0 versus 0.6) and percentage of females that spawn at least once (80–82 versus 25%). Biochemical composition of eggs presented no significant differences among treatments. FA profile of eggs indicated that high spawning activity performed by females in FLOC+FF treatment was reflected in lower mean levels of EPA, DHA and sum of polyunsaturated fatty acids (n‐3) and (n‐6). The better reproductive performance demonstrated by females raised in biofloc justified the application of this technology in F. duorarum broodstock.     

The effects of elevated pCO2 on growth,shell production and metabolism of cultured juvenile abalone,Haliotis iris

Reduced seawater pH and elevated pCO₂ are important considerations in tank‐based abalone aquaculture, while sea‐based farms may be at risk to ocean acidification reductions in pH. Juvenile Haliotis iris (5–13 and 30–40 mm shell length) were reared in two, 100‐day experiments at ambient pH_nbs (~ 8.1, 450 μatm CO₂), pH 7.8 (~1000 μatm CO₂) and pH 7.6 (~1600 μatm CO₂). Seawater pH was measured and adjusted automatically by bubbling CO₂ into water in replicated flow through tanks. Two separate trials were run, in winter (8.8°C) and summer (16.5°C). Survival and growth were monitored every 30 days, and post experiment measurements of morphometrics and respiration rate undertaken. Growth of shell length and wet weight were negatively affected by reduced pH, with a 2 to 3‐fold reduction in growth of both size classes between ambient and pH 7.6 treatments in the summer experiment. For small juveniles, growth reductions were in conjunction with decreases to shell weight, while large juveniles showed greater resilience in shell production. No changes to respiration rate occurred, suggesting that juveniles may maintain physiological functioning while tolerating dissolution pressure or that they are unable to upregulate metabolism to compensate for pH effects. These data show that CO₂ driven reductions in pH can impact growth, metabolism and biomineralization of abalone, and indicate that water quality and ocean acidification are of importance in aquaculture of the species.     

A tale of two seas: a meta‐analysis of crustacean stocks in the NE Atlantic and the Mediterranean Sea

Meta‐analysis of marine biological resources can elucidate general trends and patterns to inform scientists and improve management. Crustacean stocks are indispensable for European and global fisheries; however, studies of their aggregate development have been rare and confined to smaller spatial and temporal scales compared to fish stocks. Here, we study the aggregate development of 63 NE Atlantic and Mediterranean crustacean stocks of six species (Nephrops norvegicus, Pandalus borealis, Parapenaeus longirostris, Aristeus antennatus, Aristaeomorpha foliacea and Squilla mantis) in 1990–2013 using biomass index data from official stock assessments. We implemented a dynamic factor analysis (DFA) to identify common underlying trends in biomass indices and investigate the correlation with the North Atlantic Oscillation (NAO) index. The analysis revealed increasing and decreasing trends in the northern and southern NE Atlantic, respectively, and stable or slowly increasing trends in the Mediterranean, which were not related to NAO. A separate meta‐analysis of the fishing mortality (F) and biomass (B) of 39 analytically assessed crustacean stocks was also carried out to explore their development relative to MSY. NE Atlantic crustacean stocks have been exploited on average close to F_MSY and remained well above B_MSY in 1995–2013, while Mediterranean stocks have been exploited 2–4 times above F_MSY in 2002–2012. Aggregate trends of European crustacean stocks are somewhat opposite to trends of fish stocks, suggesting possible cascading effects. This study highlights the two‐speed fisheries management performance in the northern and southern European seas, despite most stocks being managed in the context of the European Union's Common Fisheries Policy.     

The effects of salinity on reproductive development and egg and larvae survival in the spotted scat Scatophagus argus under controlled conditions

In the present study, we report the first successful instance of controlled reproduction in Scatophagus argus, which has recently emerged as a new aquaculture resource. The controlled reproduction process for S. argus was optimized with regard to salinity acclimation. Gonadal maturation was affected by salinity in both sexes. Levels of plasma 17β‐estradiol (E₂) and 11‐ketotestosterone (11‐kT) were salinity dependent and increased significantly with the duration of acclimation. Plasma levels of gonadal steroids were higher in fish held at 25‰ salinity. The highest gonadosomatic indices (GSI), 15.1 ± 1.6 in the female and 6.4 ± 1.2 in the male, were also observed at 25‰ salinity. Nevertheless, the optimal salinity for S. argus embryonic development and larval culture was 15‰. Thus, the salinity requirement for gonadal maturation and early development are quite different. The use of advanced reproductive technologies combining salinity acclimation and stimulation of luteinizing hormone‐releasing hormone analog (LHRH‐A₂) resulted in a fertilization rate of 83.2%–91.3% and embryonic survival rates of over 90%. Embryos of S. argus at the 2‐cell, blastula, gastrula and pharyngula stages were observed. Most embryos hatched after 21.0 hr of incubation at 28.0 ± 1.0°C. The development of larvae into juveniles was completed at 40–45 days posthatch (dph). In this study, we provide information about the controlled reproduction of S. argus and identify the optimal environmental parameters for S. argus embryonic and larval culture, with the aim of developing reliable reproductive techniques for its mass production.     

Dry or wet? What is the best choice to determine gonadosomatic and hepatosomatic indexes in females of Macrobrachium amazonicum?

The gonadosomatic (GSI) and hepatosomatic (HSI) indexes are widely used for the evaluation of reproductive biology in crustaceans. However, the use of either wet or dry weight for estimating these indexes is not standardized in the literature. Here, we compare the GSI and HSI indexes based on wet and dry samples of females of Macrobrachium amazonicum from populations with different phenotypes (large and small‐size prawns) as a model. In our analysis, for GSI, the application of wet weight tended to overestimate the values recorded in the initial (I‐II) and intermediate (III) stages of ovarian development, and underestimate the results in the final (IV‐V) stages when compared to the use of dry weight. This could be attributed to the reduction in cytoplasmic organelles and water content of the cytosol due to the increase in yolk and lipids in the oocytes throughout ovarian development. For HSI, no significant differences were detected between wet and dry samples. However, the dry HSI computed at all stages of development was overestimated when compared to the use of wet samples, and only the hepatopancreas of females at the final stage (V) showed a significant decrease in water content. Thus, our results indicate that M. amazonicum females maintain constant hepatopancreatic reserves throughout ovarian development. In this way, the use of dry weight is more adequate to estimate GSI and HSI in this species.     

How “The Blob” affected groundfish distributions in the Gulf of Alaska

We investigated the distributional shifts of groundfish in response to anomalous ocean conditions, particularly the recent anomalously warm period (2014–2016; “The Blob”), based on data from ten Gulf of Alaska bottom trawl surveys conducted by the Alaska Fisheries Science Center during 1996–2015. Six groundfish species were considered: Pacific cod (Gadus macrocephalus), arrowtooth flounder (Atheresthes stomias), walleye pollock (Gadus chalcogrammus), Pacific ocean perch (Sebastes alutus), northern rock sole (Lepidopsetta polyxystra), and southern rock sole (Lepidopsetta bilineata). Ontogenetic differences were examined by dividing data for each fish species into size classes. Our study demonstrated that after accounting for size‐specific depth preferences, the spatial responses of groundfish to anomalous ocean conditions differed by species and foraging guild in the central Gulf of Alaska. Pacific cod and arrowtooth flounder showed similar responses to ocean warming, but different responses to cooling. In general, Pacific cod moved to deeper depths in warmer years and moved to shallower depths in colder years. Arrowtooth flounder also moved deeper in warmer years. However, in colder years, large arrowtooth flounder (>40 cm) shifted toward shallower depths while smaller‐sized fish shifted toward deeper depths. In warmer years, large pollock (>30 cm) moved to deeper waters while smaller pollock (10–20 cm) moved to shallower waters. Pacific ocean perch exhibited an opposite response to thermal changes in habitat compared with Pacific cod and arrowtooth flounder. They moved deeper in colder years, but there was no clear change in depth as a function of size in response to warmer habitat.     

Effects of dietary soy isoflavones on estrogenic activity,cortisol level,health and growth in rainbow trout,Oncorhynchus mykiss

Soy isoflavones (the phytoestrogens genistein, daidzein and glycitein) may act as estrogen receptor agonists or antagonists. The aim of this study was to examine the effect of dietary isoflavones on growth, reproduction and health in rainbow trout (Oncorhynchus mykiss). Rainbow trout fed three experimental diets containing different concentrations of isoflavones (0, 500 and 1,500 ppm). Growth, estrogenic activity, plasma estradiol levels, gonadal development, state of stress and histological changes in selected tissues were evaluated at the end of 70 days. Neither growth performance nor the relative mRNA levels of Insulin Growth Factor I (igf‐I) in the liver were influenced by different levels of dietary isoflavones. Plasma and liver vitellogenin (VTG) protein levels and plasma 17‐β‐estradiol (E₂) were unaffected by treatments, although the correlation between plasma levels of E₂ and VTG densitometry values was significant (p < .05). The fish gonadosomatic index (GSI) did not significantly differ among the three experimental groups but correlated with plasma VTG densitometry values (p < .05). Plasma, muscle and fin cortisol concentrations fell within the normal welfare range and were not correlated with isoflavone levels. Histologically, the distal intestine showed a normal morphology with well‐differentiated enterocytes and in the liver hepatocytes were also normal. A supranuclear accumulation of lipid droplets in enterocytes and some lipid droplets in hepatocytes were observed in all tested groups, suggesting an impact of basal dietary lipid on transport/metabolism of fat in the fish. Overall, the present results suggest that the doses of isoflavones tested do not compromise rainbow trout reproduction, growth and health.     

Effects of altered photoperiod regimes during winter on growth and gonadosomatic index in Arctic charr (Salvelinus alpinus) reared in freshwater

The short‐ and long‐term effects of altered photoperiods during winter on growth and final gonadosomatic index (GSI) were investigated in 178 individually tagged 2‐year‐old smolt Arctic charr from an anadromous strain. The fish were reared at ambient temperature (2.3–12.5°C) for 18 months and reared at five different photoperiods. One group was reared on constant LD16:8 (light–dark, N = 40) photoperiod and a second group on continuous light (LD24:0, N = 32) throughout the experimental period. Three groups of fish were moved from LD16:8 to LD24:0 for 44 days and subsequently back to LD16:8, that is early winter light group (Early WL: 17 November–5 January; N = 35), Mid WL group (5 January–23 February; N = 38) and Late WL group (23 February–6 April; N = 33). No differences in growth were found for females, whereas males reared at constant LD24:0 were larger (mean ± SEM, 1,780 g ± 180) compared with the Late (1,264 g ± 101) and Mid WL (1,413 g ± 120) groups towards the end the study. Exposure to continuous light during early winter significantly influenced the GSI in female Arctic charr, whereas no differences were found in the males. Female GSI (%) was lowest in the Mid WL group (1.7) and highest in the LD24:0 group (7.0). In conclusion, the present study demonstrated that application of brief continuous light treatments during January and February can possibly be used as a tool to lower subsequent female maturation in Arctic charr farming.     

A preliminary experiment regarding the natural induction of gonadal development in female Japanese eels without hormone treatment

To test whether gonadal development of female eels could be promoted without any exogenous hormone treatments, we observed the effect of water temperature manipulation. After 3–5 months of water temperature treatments, three silver eels showed higher gonadosomatic indices (GSI). In particular, one eel in the 5–15°C fluctuating temperature treatment group (5°C daytime and 15°C night‐time) had the highest GSI of 8.5 with secondary yolk globule stage oocytes of large diameter (OD; 412 μm) after 3 months, which indicated definite gonadal development compared with those in the initial states (mean GSI, 2.4; OD, 226.7 μm). The 5–15°C fluctuating temperature and constant 5°C groups had low oocyte breakdown (atretic) rates. Because daily temperature fluctuations and cold daytime water are experienced by vertically migrating silver eels in the ocean, these temperature conditions may be key maturation process components that could be useful for hormone‐free artificial maturation.     

Effects of dietary astaxanthin on the growth,innate immunity and antioxidant defence system of Paramisgurnus dabryanus

The effects of astaxanthin supplementationon the growth, innate immunity and antioxidant defence system of loach (Paramisgurnus dabryanus) were investigated in this study. A total of 450 fish (initial average weights of 3.00 ± 0.10 g) were fed five diets with graded levels of astaxanthin (0.00, 50.00, 100.00, 150.00 and 200.00 mg/kg) for 56 days. The results showed that astaxanthin supplementation significantly stimulated the growth (FBW, WG, FER, HSI), innate immunity (AKP activity in the hepatopancreas, intestinal tract, muscle and skin and LZM activity in the hepatopancreas, intestinal tract and skin), antioxidant ability (T‐SOD, GSH‐PX and CAT activities and T‐AOC, GSH and MDA contents in the hepatopancreas, intestinal tract, muscle and skin) of loach. Moreover, dietary astaxanthin supplementation significantly up‐regulated the relative mRNA levels of Nrf2 and Maf, and down‐regulated the relative mRNA level of Keap1 in the hepatopancreas when the supplementation levels of astaxanthin were 50–200 mg/kg. In conclusion, the diets with 100–151.06 mg/kg astaxanthin supplementation were optimal for loach, which based on the growth, immunity and antioxidant‐related indicators, and the astaxanthin supplementation regulated the antioxidant ability partially referring to Keap1‐Nrf2 signallings.     

Heritability of economically important traits in the Atlantic cod Gadus morhua L

During the development of breeding programme for Atlantic cod Gadus morhua L., in Iceland, genetic parameters were estimated for 1402 individuals, which were assigned with DNA profiling to 140 dams and 70 sires. The cod was reared in cages on the eastern and western coasts of Iceland from 2004 to 2005. At the average body weight of 1.8 kg, the estimated heritability (h² ± SE) for body weight, gutted weight and the condition factor (CF) were 0.31 ± 0.06, 0.34 ± 0.04 and 0.24 ± 0.06 respectively. Genetic correlation (r_G) in body weight between the two rearing locations was estimated as 0.95, which reflects a low G × E interaction. The estimated heritability for hepatosomatic index (HSI) and fillet yields was 0.061 ± 0.04 and 0.04 ± 0.04 respectively. The HSI and fillet yields were highly genetically correlated with body weight or 0.67 and 0.82 respectively. The genetic correlation between the CF and body weight was estimated as 0.31. There appears to be substantial amount of additive genetic variation for body weight suggesting that selection is likely to be successful. Low heritability for fillet yields and the HSI indicates less promise of genetic improvement. Assigning of parentage to individuals with DNA profiling was 80% successful.     

Effect of dietary protein and lipid levels on gonadal development of female redclaw crayfish Cherax quadricarinatus

The effect of two crude dietary protein (26% and 32% P) and two lipid levels (4.7% and 12% L) on gonadal development of female redclaw crayfish Cherax quadricarinatus was determined. The gonadosomatic index (GSI), hepatosomatic index (HSI), biochemical composition of gonad and hepatopancreas, oocyte diameter and frequency of the developmental stage of oocytes were analysed. The GSI was significantly less using 26% P to 4.7% L. A significant interaction between P and L content was found for GSI. A significantly higher HSI value was obtained when L was 12%. P content in the hepatopancreas was significantly higher using 32% P and 4.7% L. The maximum L content in the hepatopancreas was obtained from the 32% P and 12% L diet. A significant interaction between P and L content was found for L content in the hepatopancreas. A higher frequency of post‐vitellogenic oocytes was obtained with diets containing 32% P. There was an interaction between dietary P and L level causing lipid accumulation in the hepatopancreas and changes in GSI. For an optimum 32% P, excess dietary lipid is bioaccumulated in the hepatopancreas, indicating that there is excess available energy. When the P and L levels are restricted, there is a limited gonad development, thus affecting overall reproduction in female C. quadricarinatus.     

Ovarian re‐maturation following the first spawning in the Chinese mitten crab,Eriocheir sinensis (H. Milne‐Edwards)

The present study investigated the external and histological changes in the ovary and measured the gonadosomatic index (GSI) and hepatosomatic index (HSI) during the re‐maturation of the Chinese mitten crab Eriocheir sinensis. The results show that the ovarian re‐maturation cycle of this crab species can be divided into four stages, i.e. Stage I: the ovary had an X shape and appeared milky white or with a mottled buff colour, and the dominant gametocyte at the stage were oogonia (OG, 28.3%) and previtellogenic oocytes (PR, 31.6%); Stage II: the ovary appeared light yellow or tan in colour, dominated by endogenous vitellogeic oocytes (EN, 69.3%). The yolk globules of unreleased mature oocytes (MO) from the previous spawn were absorbed, leaving many vacuoles in the retrogressing MO; Stage III: the ovary appeared crimson red or deep purple, and although the main type of gametocyte was exogenous vitellogenic oocytes (EX), near‐mature oocytes (NO) could also be found in the late phase of the ovarian development stage; Stage IV: the ovary was ripe and filled with MO that contained large yolk globules. During the period of the second ovarian maturation cycle, the GSI increased significantly from the time just after the first spawning (P<0.01). However, although HSI appeared to decrease within days after spawning (DAS), no significant correlation was found between GSI and HSI or between HSI and DAS (P>0.05). Furthermore, the final GSI and the volume of MO of E. sinensis during the second maturation cycle were drastically lower than those of the first maturation cycle.     

Allometric growth patterns and development in larvae and juveniles of thick‐lipped grey mullet Chelon labrosus reared in mesocosm conditions

Allometric growth and ontogeny were studied in thick‐lipped grey mullet Chelon labrosus reared in mesocosms from 1 to 71 day post hatching (dph). Multivariate allometric analysis of morphometric growth distinguished three distinct developmental stanzas separated by two morphometric metamorphosis lengths (L_m1 = 4.46 ± 0.06 mm; L_m2 = 28.56 ± 1.04 mm). Body mass growth also showed three distinct episodes separated by two inflections, correlated with morpho‐functional changes. First episode concerned pre‐flexion larvae and ended around 4.5 mm‐L_T (14‐dph), coinciding with estimated L_m1. It was distinguished by reduced growth, but intense morphogenesis and differentiation processes. Organogenesis and allometric changes indicated that development priorities concerned feeding efficiency, by improving detection ability (sensory system development), ingestion capacity (head growth) and assimilation performance (digestive system differentiation), together with respiration efficiency (gill development). Second episode concerned post‐flexion larvae and, ended around 8.6 mm‐L_T (25‐dph). It was distinguished by fast growth of trunk and tail, acquisition of adult axial muscle distribution and completion of gill filament development, improving locomotion and oxygenation performances. It corresponded to transition towards metamorphosing stage as indicated by later isometric growth, musculature maturation and acquisition of juvenile phenotype. Metamorphosis seemed to end at L_m2, suggesting to avoid zootechnic handling before this size.     

Reproductive cycle and plasma levels of steroids in male Eurasian perch Perca fluviatilis

From April 1995 to April 1996, the annual reproductive cycle of male Eurasian perch Perca fluviatilis was studied at the Lindre Center (Moselle, France). At monthly intervals, five males (mean body weight of 133 ± 43 g and total length of 175 ± 9 mm) were caught. From sampled organs, the gonadosomatic (GSI), hepatosomatic (HSI) and viscerosomatic indexes (VSI) were calculated and plasma testosterone (T) and 11-ketotestosterone (11KT) levels were measured. After the spawning period in mid-April, GSI and HSI dropped and VSI increased to 3.8 ± 0.1 %. In September, GSI reached its maximum (8.5 ± 1.8 %). At this time, spermatocytes, spermatids and spermatozoa were abundant, whereas in June only spermatogonia were observed. During winter, GSI was stable at approximately 5 %, HSI reached its maximum (1.9 ± 0.3 %) and VSI was low (2.6 ± 0.2 %). From April to November 1995, plasma T and 11KT concentrations were low (< 0.5 ng·mL^–1). Plasma T levels increased significantly in December and reached peak levels (12.3 ± 2.1 ng·mL^–1) in January, then decreased in February and increased again until spawning in April (6.8 ± 2.1 ng·mL^–1). This second elevation could be related to the beginning of a new spermatogenic cycle. Plasma levels of 11KT increased significantly from October to February 1996 (4.9 ± 1.1 ng·mL^–1). From February to the spawning period (April 1996), plasma 11KT decreased significantly, but values were significantly higher than those measured in fall. Males were spermiating from January to spawning in April.