Changes in plasma insulin-like growth factor-I levels in the precociously maturing amago salmon, Oncorhynchus masou ishikawai

Seasonal changes in plasma levels of insulin-like growth factor I (IGF-I) in precociously maturing amago salmon (Oncorhynchus masou ishikawai), which matured as 1-year-olds, have been investigated. Profiles of plasma IGF-I levels were compared with changes in growth and maturity, and plasma growth hormone (GH) and thyroxine (T₄) concentrations. The maturity of the fish was determined by calculating the gonadosomatic index; in November, 100% of males and 89% females matured. In both males and females, plasma IGF-I levels increased from March to August, and subsequently, plasma IGF-I levels in the early maturing males and females declined gradually and were maintained at lower levels during the spawning period in November. Plasma GH levels were high in April, and then declined gradually through September. Thereafter, in early maturing fish, a slight increase in plasma GH levels was observed in October and November. No significant changes in plasma T₄ levels were found in the precociously maturing fish. In sharp contrast, plasma IGF-I levels in immature fish remained elevated through September, reaching a peak in October, and then gradually declined in November. In immature females, plasma T₄ and GH levels were elevated in August, reached their maximum in September and then gradually declined until November.     

The modulating effect of vitellogenin on the synthesis of 17β-estradiol by rainbow trout (Oncorhynchus mykiss) ovary

In vivo induction of vitellogenin (VTG) in response to the administration of 17-estradiol (E₂) was achieved and the protein was isolated by gel filtration column chromatography of plasma samples. Adult female trout were injected with the vitellogenic fraction every ten days from July to November and levels were measured by RIA from September to December. The results showed a significant decrease (p<0.01) in plasma E₂ levels in injected females compared with the controls. In December, after finishing the treatment, the plasma E₂ concentration increased, in injected females to reach a level similar to that of control females at vitellogenesis. The in vitro study showed that in early vitellogenic oocyte (from September) the presence of the vitellogenic fraction in the incubation medium causes a significant decrease (p<0.01) in the synthesis of E₂ by the oocytes. These data suggest that the concentration of the VTG into the oocyte can alter VTG production by the liver, moderating the production of E₂ by the ovary.     

Disparate effects of gonadal steroid hormones on plasma and liver mRNA levels of insulin-like growth factor-I and vitellogenin in the tilapia, Oreochromis mossambicus

The tilapia, Oreochromis mossambicus, exhibits a sexually dimorphic pattern of growth, males growing larger than females. We examined the effects of E₂ and DHT on the GH/IGF-I axis and on VTG production in the tilapia. Sexually mature tilapia were injected with 5 μg g body weight of E₂ (males) or DHT (females) every 5 days for a total of 3 injections. Female tilapia had significantly higher plasma GH levels than males. However, plasma and liver mRNA levels of IGF-I were significantly lower in females than in males, whereas VTG levels in both the plasma and liver mRNA were significantly higher in females than in males. Although significant amounts of VTG were detected in control males (8 ± 0.3 μg ml), the levels in control females (3000 ± 500 μg ml) were about 400 times higher than in males. Males treated with E₂ exhibited a female-like GH/IGF-I profile. That is, they had significantly elevated levels of plasma GH with lower plasma IGF-I and liver IGF-I mRNA levels. Estradiol treatment significantly elevated both plasma and liver mRNA VTG levels. Dihydrotestosterone treatment in females induced a male-like GH/IGF-I profile: plasma GH levels were significantly reduced, whereas plasma and liver IGF-I mRNA levels were significantly elevated. Both plasma and liver mRNA levels of VTG were not altered by DHT treatment. Pituitary GH mRNA levels were similar in all treatment groups. These results clearly indicate that estrogens and androgens feminize and masculinize the GH/IGF-I axis, respectively. This revised version was published online in July 2006 with corrections to the Cover Date.     

Sex differences in circulating steroid hormone levels in the red drum, Sciaenops ocellatus L.

Steroid profiles of cultured and captive red drum (Sciaenops ocellatus L.) were investigated to evaluate the potential use of circulating sex steroid levels as a tool for gender identification in this species. Cultured 18‐month‐old fish were maintained on a 120‐day shortened photothermal cycle to induce precocious maturation. Additionally, wild‐caught fish were maintained in captivity under simulated natural photothermal conditions from late spring to early fall. Circulating 11‐ketotestosterone (11‐KT) levels were significantly higher in males compared with females during the early stages of gonadal growth in both cultured and captive fish. Plasma testosterone (T) levels showed a similar trend; however, the differences were significant only when males were already producing sperm. 17β‐estradiol (E₂) concentrations were low in males and females before gonadal recrudescence but increased significantly with the progression of vitellogenesis in females. These results show that a test using a minimum concentration of circulating 11‐KT could be developed to differentiate between sexes in the early stages of gonadal maturation in red drum. Moreover, plasma E₂ concentrations could be used to identify vitellogenic females. The two steroids considered together could help avoid possible error in gender identification due to unusually high levels of certain steroids encountered in some individuals.     

Purification,characterization and immunoassay of striped bass (Morone saxatilis) vitellogenin

The egg yolk precursor, vitellogenin (VTG), was purified from blood plasma of striped bass by chromatography on hydroxylapatite or DEAE-agarose. The fish were first implanted with estradiol-17β (E₂), which induced vitellogenesis. A rabbit antiserum (a-FSPP) raised against plasma from mature female striped bass, and then adsorbed with mature male plasma, was used to detect female-specific plasma protein (FSPP) in the chromatography fractions. Striped bass VTG (s-VTG) was collected from the peak fraction that was induced by E₂, reacted with a-FSPP, and contained all detectable phosphoprotein. It appeared as a single band (M_r ≂ 170,000) in SDS-PAGE or Western blots using a-FSPP, and as a pair of closely-spaced phospholipoprotein bands in native gradient-PAGE, suggesting that there is more than one circulating form of s-VTG. The relationship of s-VTG to the yolk proteins was verified using a-FSPP. The antiserum reacted with the main peak from gel filtration of saline ovary extracts, and it specifically immunostained the two main bands in Western blots of the extracts and the yolk granules of mature oocytes. The amino acid composition of s-VTG was similar to that of VTG from other fish and Xenopus. A radial immunodiffusion assay for s-VTG was developed using a-FSPP and purified s-VTG as standard. The s-VTG was not detected in blood plasma of males, immature females, or regressed adult females, but plasma s-VTG levels were highly correlated with plasma E₂ and testosterone levels, and oocyte growth, in maturing females. The results indicate that the maturational status of female striped bass can be identified by s-VTG immunoassay.     

Involvement of sex steroids,luteinizing hormone and thyroid hormones in upstream and downstream swimming behavior of land-locked sockeye salmon <Emphasis Type="Italic">Oncorhynchus nerka</Emphasis>

The involvement of testosterone (T), estradiol-17β (E₂), 11-ketotestosterone (11-KT), 17,20β-dihydroxy-4-pregnene-3-one (DHP), luteinizing hormone (LH), thyroxine (T₄), and triiodothyronine (T₃) in the regulation of downstream and upstream movement (swimming behavior) was investigated in land-locked sockeye salmon Oncorhynchus nerka, using an artificial raceway. During the downstream migratory period, T implant resulted in high plasma T levels and inhibited the occurrence of downstream swimming behavior (negative rheotaxis) in yearling (1+) immature smolts. In terms of upstream behavior, 2-year-old (2+) males exhibited high plasma T and 11-KT levels, while 2+ females had elevated T and DHP levels. In 1+ immature fish, a T implant induced upstream swimming behavior (positive rheotaxis). In experiments 1 and 3, the plasma T₄ and T₃ levels of non-migrants tended to be higher than those of migrants. In contrast, no marked changes in plasma and pituitary LH were found in both downstream and upstream migrants. These results suggest that sex steroids, such as T, play significant roles in the regulation of downstream and upstream swimming behaviors in land-locked sockeye salmon.     

Photoperiodic manipulations of the reproductive cycle of sea bass (Dicentrarchus labrax) and their effects on gonadal development, and plasma 17ß-estradiol and vitellogenin levels

The annual profile of plasma vitellogenin (VTG) and 17ß-estradiol (E₂) levels, as well as gonadal development and spawning characteristics were investigated in captive female sea bass (Dicentrarchus labrax). Endocrine and gonadal changes were studied in fish reared under natural conditions or exposed to manipulated photothermal cycles. In natural conditions of photoperiod and temperature, sea bass spawned from February through March (East coast of Spain, 40°N 0°E). One or two months of constant long-days (15L/9D) in a constant short-day photoperiod regime (9L/15D) all-year-round, given early in the year (March and March–April), advanced spawning by 3 months. The same treatment applied later in the year (September–October) delayed spawning by 1 month, compared to controls.In all groups, changes in plasma VTG levels were correlated with E₂ levels, oocyte growth and spawning time. In control females, VTG was low (<100 ng ml^-1) during the summer, until its first surge in plasma 4 months before the beginning of spawning. The VTG (3.1 ± 0.3 mg ml^-1) and E₂ (4.1 ± 0.5 ng ml^-1) levels showed a single annual peak during late vitellogenesis, the time of the highest proportion of vitellogenic oocytes in the ovary. Constant high levels of VTG (1–1.4 mg ml^-1) and E₂ (1.6–1.9ng ml^-1) were maintained during the entire spawning time, together with the presence of vitellogenic oocytes, suggesting the existence of several waves of oocyte growth in the ovary and thus, several spawns per female. Endocrine profiles and oocyte development in fish exposed to constant photoperiods were similar to controls, but were shifted in time in relation to the displacement of the spawning time. In the fish showing advanced spawns, the duration of the gametogenic proces was compressed when compared to controls. The differences observed in the evolution of the reproductive-related factors in the advanced groups, which were exposed to a reduction in temperature to 15°C, suggest an influence of the temperature in the early stages of the reproductive cycle in sea bass.     

Effects of individual and binary mixtures of estrogens on male goldfish (Carassius auratus)

Adverse effects of five typical environmental estrogens, namely estrone (E₁), 17β-estradiol (E₂), 4-n-octylphenol (4-n-OP), 4-n-nonylphenol (4-n-NP) and bisphenol A (BPA) on adult male goldfish (Carassius auratus) were investigated both individually and in binary mixtures, using serum vitellogenin (VTG) induction and gonadosomatic index (GSI) as the endpoints. Doses of individual and binary mixtures of estrogens were chosen at broad ranges. Five individual estrogens induced common dose-dependent increases of serum VTG in the experimental fish when injection doses of the estrogen series were comparatively low. The levels of VTG induction in fish descended after peaked at a certain dose of the individual estrogen. Significant GSI decreases were observed in fish treated by all dose series of E₁ and E₂, and comparatively high doses of 4-n-OP, 4-n-NP and BPA when compared with that of solvent control (SC). Effects of binary mixtures of the five typical estrogens on VTG induction in male goldfish were in additive manner at low-effect doses, but divergences occurred at high dose levels, with the predicted effects by additive manner exceeding those were observed. All of GSI of fish treated by the binary mixtures were about or lower than 10^?3 %. Serious atrophy of gonads was observed in all the mixture treatment groups when compared with that of SC. These findings highlight the potential reproductive risk of fish resulted from existing mixtures of hormones in the aquatic environment, and they have important implications for environmental estrogen hazard assessment.     

The purification and development of a quantitative enzyme linked immunosorbent assay (ELISA) for the measurement of vitellogenin in diploid and triploid brook trout (Salvelinus fontinalis)

Vitellogenin (VTG) was purified from the plasma of estradiol-17β (E₂) treated male brook trout (Salvelinus fontinalis; bt) using gel filtration and anion exchange chromatography. An antiserum to bt-VTG was raised in rabbits, then used to detect bt-VTG by Western blot analysis. Purified bt-VTG and its antibody were then used to develop an antibody-capture, competitive enzyme-linked immunosorbant assay (ELISA). Confirmation of the purified protein as bt-VTG was based on the characteristics of high molecular weight (∼562 kDa), dominant plasma protein in vitellogenic females and induction by exogenous E₂ treatment in males. The antiserum recognized a major 184 kDa polypeptide as well as minor bt-VTG degradation products (150–66 kDa) in purified bt-VTG and in plasma from vitellogenic females. Low levels of antibody cross reactivity were shown with plasma from nonvitellogenic females, control rabbit serum, and several other antisera known to not contain VTG. The ELISA had a minimum detection limit of 8 ng ml⁻¹ and intra- and inter-coefficients of variation less than 9% and 15%, respectively. The ELISA demonstrated parallel binding slopes among dilution curves of purified bt-VTG standard and plasma from diploid and triploid brook trout females. Using the ELISA, maximum plasma VTG levels of 93.5±33.6 mg ml⁻¹ were detected in vitellogenic diploid females, whereas only 0.18±0.15 mg ml⁻¹ were detected in triploid females of the same age (n=5 for each). Diploid and triploid males cohabitating with vitellogenic females showed measurable levels of plasma VTG during vitellogenesis in females (i.e., 0.17 and 0.06 mg ml⁻¹, respectively (n=1)). This revised version was published online in August 2006 with corrections to the Cover Date.     

Seasonal changes in channel catfish thyroid hormones reflect increased magnitude of daily thyroid hormone cycles

Channel catfish (Ictalurus punctatus) in pond culture, sampled once per day, have been reported to exhibit significant seasonal cycles in the thyroid hormones thyroxine (T₄) and 3,5,3′-triiodothyronine (T₃), rising from levels generally below 2 ng/ml in January to above 8 ng/ml in July. To determine if daily thyroid hormone cycles underlie these seasonal changes, we blood sampled groups of 20 catfish (10 males and 10 females) in the morning (approx. 1 h after sunrise), midday, and evening (approx. 1.5 h before sunset) on January 9, April 4, and July 29. From January to July, pond temperatures rose from 7 ° to 32 °, associated with significant (p < 0.05) increases in mean fish weight (from 477 to 1052 g) and in monthly mean food consumption (from 34 to 474.7 g/kg fish). On all three dates, significantly (p < 0.05) greater levels of both hormones (except T₃ in April) were found in midday and evening compared to morning samples. In January, the daily change was small (from morning to midday, mean T₃ rose from 2.2 to 3.6 ng/ml and mean T₄ from 2.3 to 4.8 ng/ml), whereas in July it was considerably greater (from morning to evening, mean T₃ rose from 7.2 to 17.8 ng/ml, and T₄ from 9.0 to 22.4 ng/ml). No significant differences were found between midday and evening levels, or between males and females. Additionally, no seasonal phase-shifting of cycles was apparent. A subset of animals was examined to evaluate the potential contribution of peripheral mechanisms in generating these seasonal and daily cycles. Whereas we observed only minor changes in thyroid hormone binding to plasma proteins during any single day, a significant seasonal increase in the ratio of free T₄:free T₃ indices (from a mean of 1.3–1.5 in January to 2.0–2.1 in July) indicated enhanced T₃ binding by plasma proteins in July. Furthermore, in vitro hepatic T₄ and T₃ deiodination activities showed across dates no significant change in T₄ outer-ring deiodination to produce T₃ (ranging from a mean of 53.1 to 70.1 pmol T₄ deiodinated/h/mg microsomal protein), but a significant (p < 0.05) decrease in T₄ inner-ring deiodination to degrade T₄ to 3,3′5′-triiodothyronine (from a mean in January of 2.4 to 0.65 pmol T₄ deiodinated /h/mg protein in April) and a significant (p < 0.05) decrease in T₃ inner-ring deiodination to degrade T₃ to 3,3′-diiodothyronine (from a mean in January of 115.5 to 3.1 pmol T₄ deiodinated/h/mg protein in July). These results demonstrate that channel catfish under conditions of natural temperature and photoperiod exhibit robust daily cycles in total plasma T₄ and T₃ similar in magnitude to those reported for other fish species held under controlled laboratory conditions. These cycles maintain a similar phase throughout the year, indicating that apparent seasonal increases in thyroid hormones are not due to phase-shifting of daily cycles. However, seasonal studies sampling fish only in the morning would underestimate the magnitude of the annual changes in blood thyroid hormones. Thyroidal status, as judged from total plasma T₄ and T₃ levels in the afternoon, is greatest in July, coinciding with the postspawning peak in food consumption and growth. Enhanced T₃ plasma protein binding and a shift from predominantly hepatic inner-ring deiodination in winter to outer-ring deiodination in summer suggest that peripheral mechanisms contribute to the generation of these seasonal changes.     

The effect of whole body lipid on early sexual maturation of 1+ age male chinook salmon (Oncorhynchus tshawytscha)

Early sexual maturation of male chinook salmon (maturation 1 to 4 years prior to females in the same age class) results in reduced effectiveness of stock enhancement programs and a financial loss to the salmon farming industry. Previous studies in Atlantic salmon have shown that the age of maturity in males is affected by growth and/or body energy stores, but the relative roles of these two factors are not well understood. Therefore, an experiment was designed to determine when spermatogenesis was initiated, to characterize the endocrine changes during the onset of puberty in male salmon, and to determine if the level of whole-body lipid affects the incidence of early male maturation in a wild stock (Yakima River) of 1+ spring chinook salmon. Fry were fed a commercial diet from February until August and were then divided into groups of 320 fish (mean weight, 5.6 g) and fed one of five experimental diets (two replicate groups/diet) containing 4%, 9%, 14%, 18% or 22% lipid and 82%, 77%, 73%, 69%, or 65% protein for 13 months. Fish were reared on natural photoperiod and ambient temperature (6°C to 16°C), and pair-fed to a level based on the tank with the lowest feed consumption. Fish were weighed monthly and sampled to determine body composition, pituitary follicle-stimulating hormone (FSH) and luteinizing hormone (LH) levels, plasma insulin-like growth factor I (IGF-I) levels, and stage of gonadal development.

Throughout the experimental period the mean fish weight was similar among treatment groups. However, from December through the end of the experiment in the following September, maturing males were significantly larger than nonmaturing fish. Initial lipid levels in 0-age experimental fish were near 6%, which is similar to wild fish of the same stock and age captured in the Yakima River during August. Fish fed diets containing more than 4% lipid increased in whole-body lipid content during the first 2 months of feeding and then maintained at relatively constant levels during the course of the experiment. Whole-body lipid levels for the dietary treatment groups averaged 5.6%, 7.1%, 8.2%, 9.4%, and 9.6% from October through the following September.

Based on histological examination of the testes of experimental fish, type B spermatogonia and primary spermatocytes were first observed in some of the yearling males during November. These were designated maturing males. Pituitary FSH levels were significantly higher in maturing than nonmaturing males at this time and for the remainder of the study. Pituitary FSH levels increased as spermatogenesis proceeded in maturing fish, whereas pituitary LH levels increased in maturing 1+ males only during July and August, when testes were in late stages of spermatogenesis and in September during spermiation. Plasma IGF-I levels were significantly higher in maturing males than nonmaturing fish from December through the end of experiment. Since maturing males were significantly larger than nonmaturing fish of both sexes from December through September, the difference in IGF-I levels could be due to differences in growth or due to maturation.

The percentage of maturing males was significantly influenced by whole-body lipid, increasing from 34% in fish fed the 4% lipid diet to 45% in fish fed the 22% lipid diet. These data suggest that whole-body lipid levels influenced the incidence of maturation of male spring chinook salmon. In addition, both endocrine and histological indicators suggest that maturation was initiated in males approximately a full year prior to the time the fish will spawn.     

Hormonal changes accompanying sexual maturation in captive milkfish (Chanos chanos Forsskal)

Steroid hormone profiles accompanying sexual maturation in captive milkfish are described. There were no significant differences in levels of serum estradiol 17- (E₂) and testosterone (T) between immature male and female fish. Mean E₂ levels rose from 0.54±0.11 ng/ml in immature females (Stage 1) to 4.53±1.16 ng/ml in vitellogenic females (Stage 5), while T levels increased from 2.06±0.28 ng/ml to 38.4±9.26 ng/ml. E₂ and T levels were positively correlated to GSI and oocyte diameter. In males, serum T levels increased from 2.5±0.40 ng/ml in immature males to 27.73±5.02 ng/ml in spermiating males. A significantly higher T level was found in males with thick and scantly milt (spermiation index, SPI, 2) compared to males with scanty milt (SPI, 1) or males with copious, fluid milt (SPI, 3).Serum levels of E₂ and T, and the GSI in females rose significantly during the breeding season (April–June 1983). The levels of both steroids dropped below 1 ng/ml in spent females sampled in succeeding months. In immature males, T levels ranged from 1.11 ng/ml to 2.78 ng/ml and rose significantly to 21.52±8.38 ng/ml during the breeding season when GSI peaked. Serum T levels dropped to around 10 ng/ml in the succeeding months when only spent or regressed males were sampled.     

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.     

The reproductive physiology of three age classes of adult female diploid and triploid brook trout (Salvelinus fontinalis)

Triploid female fish show impaired gametogenesis and are unable to produce viable offspring. The reproductive physiology of artificially-induced triploid female salmonids has been well described up until the time of first sexual maturation in diploids, but few reports exist for older triploids. This study reports the influence of triploidy on growth, ovarian development and reproductive endocrinology among three age classes of female brook trout (Salvelinus fontinalis) in comparison to sibling diploids. Triploids were larger than diploids for most of the study period, but the difference was statistically significant only during maturation and spawning of 2⁺ diploids. Plasma estradiol-17 (E₂), testosterone (T) and vitellogenin (VTG) levels in triploids were generally lower than in diploids, and VTG was the only parameter to show seasonal fluctuations resembling those of diploids. Triploids showed significantly lower GSI and total oocyte number than diploids of similar age, and only half of all triploids sacrificed during the study (n=56) had developing oocytes in their ovaries. At age 3⁺, 13 of 19 triploid females had oocytes at various stages of development, including perinucleolar, yolk vesicle and yolk globule stages. In addition, three of these fish had collectively produced 72 mature stage oocytes. Thus, whereas diploid brook trout can produce mature oocytes as two-year-olds, triploids cannot do so until four years of age, with the number of mature oocytes being greatly reduced.     

Hormonal profile of growing male and female diploids and triploids of the blue tilapia,Oreochromis aureus,reared in intensive culture

Triploidy as a result of thermal shock exposure of fertilized eggs decreases the growth rate ofOreochromis aureus as compared to their diploid controls, but this is due to the higher female ratio present in triploids (86%) and the lower growth rate of females. When females and males are considered separately, the growth rate is not significantly different in diploids and triploids. Since triploidy results in a malfunctioning steroidogenesis in females (mainly testosterone (T) and 17β-estradiol (E₂)), but does not affect the growth rate, it is concluded that female gonadal steroids do not influence growth unless in pharmacological concentrations. These low levels of gonadal steroids are generally accompanied by higher levels of gonadotropin (GtH), but the difference is not always significant. Despite their lower growth rate diploid females have higher plasma concentrations of growth hormone (GH) during several months compared to the triploid females and diploid males. 3,5,3′-triiodo-L-thyronine (T₃) levels, however, are comparable between diploid and triploid females (except for 1 month), but higher in diploid males in 4 of the 5 months studied. 11-ketotestosterone (11kT) is always higher in males. These results indicate that the higher growth rate of males may be related to the high circulating levels of T₃ and 11kT.     

Analysis of growth, weight and relevant indices of diploid and triploid population of tench Tinca tinca (Linnaeus 1758)

This study determined biometric and weight parameters and relevant indices of diploid and triploid tench. Altogether, 137 siblings of tench were studied. The effect of ploidy level appeared in significantly better growth of triploids (P<0.001) as to biometric [total length (TL), standard length (SL), body height (BH), body width (BW)] and weight [fish weight (FW), carcass weight (CW)] parameters of T₃ of both sexes and of T₃₊ females. The effect of ploidy level also appeared as significantly higher dressing percentage (DP; P<0.001) of triploid T₃ females compared with other groups, significantly higher gonad weight (GW) and gonadosomatic index (GSI; P<0.001) of diploid T₃ females, as well as GSI and hepatosomatic index of diploid T₃₊ females. The effect of sex appeared in significantly higher (P<0.001) biometric (TL, SL, BH, BW) and weight (FW, CW) parameters of T₃ females of both ploidy levels, as well as of triploid T₃₊ females. The effect of sex also appeared as significantly higher DP (P<0.001) of males in diploid T₃ fish, as well as of males of both ploidy levels in T₃₊ fish and significantly higher GW and GSI (P<0.001) of females in diploid T₃ fish, as well as of females of both ploidy levels in T₃₊ fish. This study shows evidence for faster somatic growth and bigger final weight of triploid populations of tench compared with diploids in both age categories T₃ and T₃₊.     

Endocrine growth regulation of adult Atlantic salmon in seawater: The effects of light regime on plasma growth hormone, insulin-like growth factor-I, and insulin levels

Plasma growth hormone (GH), insulin-like growth factor-I (IGF-I), and insulin were measured in two groups of Salmo salar L. during a one-year study. The fish were reared under either a simulated natural photoperiod (SNP) from January to December or a regime of continuous light from January to June, followed by SNP until December (LL/SNP). Plasma GH levels during spring were low, and lower in the LL/SNP fish (< 0.9 ng ml^− 1) than in the SNP fish (> 1.9 ng ml^− 1), although the LL/SNP grew better (0.8% per day) than the SNP fish (0.5% per day). Plasma IGF-I levels increased transiently from January (64.7 ng ml^− 1) to maximum in late September in the LL/SNP (85.8 ng ml^− 1) and in November in the SNP group (87.3 ng ml^− 1). The ratio GH:IGF-I was lower in the LL/SNP group during spring when this group grew better than the SNP group.     

Comparative responses in rare minnow exposed to 17β-estradiol during different life stages

Present in the excrement of humans and animals, 17β-estradiol (E₂) has been detected in the aquatic environment in a range from several nanograms to several hundred nanograms per liter. In this study, the sensitivities of rare minnows during different life stages to E₂ at environmentally relevant (5, 25, and 100 ng l⁻¹) and high (1000 ng l⁻¹) concentrations were compared using vitellogenin (VTG) and gonad development as biomarkers under semistatic conditions. After 21 days of exposure, VTG concentrations in whole-body homogenates were analyzed; the results indicated that the lowest observed effective concentration for VTG induction was 25 ng l⁻¹ E₂ in the adult stage, but 100 ng l⁻¹ E₂ in the larval and juvenile stages. After exposure in the early life stage, the larval and juvenile fish were transferred to clean water until gonad maturation. No significant difference in VTG induction was found between the exposure and control groups in the adults. However, a markedly increased proportion of females and appearance of hermaphrodism were observed in the juvenile-stage group exposed to 25 ng l⁻¹ E₂. These results showed that VTG induction in the adult stage is more sensitive than in larval and juvenile stages following exposure to E₂. The juvenile stage may be the critical period of gonad development. Sex ratio could be a sensitive biomarker indicating exposure to xenoestrogens in early-life-stage subchronic exposure tests. The results of this study provide useful information for selecting sensitive biomarkers properly in aquatic toxicology testing.     

Thyroidal compensation in rainbow trout (Salmo gairdneri) fed canola meal

Rainbow trout (Salmo gairdneri Richardson) were fed either a soybean mealbased (SM) or canola meal-based (CM) diet for up to 20 weeks. Plasma thyroxine (T₄) and triiodothryonine (T₃) levels were significantly lower in the CM-fed fish sampled after 12 weeks. However, there appeared to be some compensation after 12 and 20 weeks in that the thyroid hormone levels in trout fed the CM were not significantly different from those of the SM-fed fish. Nevertheless, there was marked thyroid hyperplasia and hypertrophy in the CM-fed fish sampled at 12, 16 and 20 weeks after commencement of the experiment. Moreover, the growth rate was significantly lower in the CM-fed fish in comparison to the SM-fed fish throughout the 20 week study period.Plasma T₄ levels were similar in SM-fed fish sampled 12, 16 and 20 weeks after commencement of the experiment, but plasma T₃ levels progressively increased over this period, as did the apparent activity of the thyroid tissue based on histological criteria.Fasting for up to 8 weeks resulted in the arrested growth of the SM-fed fish, and a loss in body weight of the CM-fed animals over the 8 week period of the fast. In addition, the plasma thyroid hormone levels in the fasted fish tended to be lower than in fish fed both the SM and CM diets prior to fasting, and there was histological evidence indicating a reduced activity of the pituitary-thyroid axis. However, thyroid hyperplasia and hypertrophy were still evident in the fasted fish previously fed the CM diet indicating that the adverse affects of CM diets are not completely reversible after 8 weeks.In fish fed the CM diet for 12 weeks and then the SM diet for up to a further 8 weeks (diet C-S) there was a compensatory increase in plasma thyroid hormone levels evident within 4 weeks after the change in diet, but no apparent decrease in thyroid hyperplasia or hypertrophy. In addition, in the fish fed the C-S diet there was a marked compensatory growth rate, and an increased feed: gain ratio; body weights of this group of fish were not significantly different from those of the SM-fed animals after 20 weeks of study, indicating a considerably higher growth rate over the last 8 week period.     

Does oral 3,5,3 ′-triiodo-l-thyronine affect dietary glucose utilization and plasma insulin levels in rainbow trout (Salmo gairdneri)?

A factorial experiment was conducted to determine the effect and interaction of dietary carbohydrate level and triiodo-L-thyronine (T₃) supplementation on the growth, physiological response and plasma insulin and cortisol levels of rainbow trout. The oral administration of T₃ significantly increased the growth, protein efficiency ratio and feed efficiency of trout, indicating an increased protein and perhaps energy utilization in these fish. However, T, administration did not significantly increase the utilization of dietary glucose as an energy source by the trout. Similarly, the administration of T₃ did not significantly affect plasma insulin levels in either the fed or the fasted trout. Plasma insulin levels were significantly higher in fed trout reared on the non-T₃ supplemented high carbohydrate diet in comparison to trout reared on the low carbohydrate diets. This indicates that increased dietary carbohydrate stimulates increased insulin secretion in the trout. Therefore, although rainbow trout are not insulin-deficient, they can still be considered a diabetic-like animal due to their poor glucose tolerance. Plasma cortisol levels were not affected by diet composition and altered plasma glucose levels.