Effect of Dietary Estradiol‐17β on the Feminization of Silver Perch,Bidyanus bidyanus (Mitchell, 1838)

The silver perch, Bidyanus bidyanus (Mitchell 1838), displays sexual dimorphism in size, with females reaching larger maximum size than males. In an attempt to produce all‐female populations, larvae at 30 d posthatching were fed an estradiol‐17β (E2) diet at dosages of 0, 60, and 120 mg/kg for 30 d. Histological examination of gonads revealed that all E2‐supplemented diets resulted in significantly higher (P < 0.05) feminization rates (97.22–100%) than did the control (39.69%) but with no difference between the two E2 diets (P > 0.05). Female and male gonads were observed in fish fed the 60 mg E2/kg diet. No significant differences were observed in the survival rate, weight gain, gonad weight and length, specific growth rate (SGR), or gonadosomatic indexes, except for gonad length and SGR at the end of the experiment. Although the ovary length of fish fed the 60 mg E2/kg diet was significantly shorter than that of the control groups, no abnormalities were detected. In contrast, fish fed 120 mg E2/kg grew faster than the other fish and showed sexual dimorphism. Our results suggest that supplementation of E2 at 60–120 mg/kg diet could be applied to establish all‐female populations of silver perch.     

The effects of different proportions of the 17β‐estradiol and 17α‐methyltestosterone on growth,sex reversal and skin colouration of the electric blue hap (Sciaenochromis ahli Trewavas, 1935)

This study was performed to investigate the effects of 17β‐estradiol (ES) and 17α‐methyltestosterone (MT) on growth, development, survival, sex ratio and colour change in the electric blue hap (Sciaenochromis ahli Trewavas, 1935). The hormones were not supplemented to the control feed, while six other feeds were prepared by adding 20, 40 and 60 mg kg^?1 17β‐ES or 20, 40 and 60 mg kg^?1 17α‐MT to each, resulting in seven different feed treatments. Average live weight of the fish supplemented with these diets was 0.42 ± 0.04 g. At the end of the study, the highest weight gain was observed in fish fed 60 mg kg^?1 17α‐MT group (2.62 ± 0.11 g) and the difference with the groups fed with 17β‐ES was found to be significant. All fish fed 17α‐MT were male, while the rates of feminization in fish fed 17β‐ES at 20, 40, 60 mg kg^?1 were 91.11%, 88.88% and 93.33% respectively. Survival rates were respectively determined as 80%, 95.56%, 84.44%, 93.33%, 77.78%, 84.44% and 84.44% for the control, 20, 40, 60 mg kg^?1 17β‐ES and 20, 40, 60 mg kg^?1 17α‐MT treatments. The best colouration was achieved in the 17α‐MT groups (P < 0.05). The L* values varied between 32.98 ± 4.44 and 61.35 ± 2.19, a* values between ?7.06 ± 0.22 and ?3.42 ± 0.11, and b* values between ?7.74 ± 0.10 and 11.65 ± 0.03, while Chroma (C*) and Hue (H°_ab) angle values varied between 7.54 ± 0.22 and 13.60 ± 0.01 and between 119.76 ± 0.05 and 239.73 ± 4.86. In conclusion, the 17α‐MT feeding was found to have a greater effect on the growth, feed conversion ratio, masculunization and pigmentation of the electric blue haps than the 17β‐ES treatment.     

Masculinization of fighting fish, Betta splendens Regan, using synthetic or natural androgens

Abstract. The effects of two synthetic androgens, 17α-methyltestosterone (5–50mg/kg food), 19-nor-ethynyltestosterone (2–50 mg/kg food) and two natural androgens, 11 ketotestosterone (10–60mg/kg food) and androstenedione (20–100mg/kg food) were investigated in the fighting fish, Betta splendens Regan. Androgens were administered for 40 days from the first day of feeding. Masculinization occurred in 100% of individuals fed 8, 15, 60, 90 mg/kg food 19–nor–ET, 17α–MT, 11–KT and AT respectively. Mortality due to treatment of natural steroids was significantly less than that with the synthetic steroids. Sex–reversed males were sexually functional and their genotype was identified by progeny testing. Sex-reversed males produced 100% female monosex when mated with normal females, indicating that the mechanism of sex determination in this fish is homogametic female and heterogametic male.     

Effects of Estradiol Valerate on Steroid Hormones and Sex Reversal of Female Rice Field Eel,Monopterus albus (Zuiew)

The rice field eel, Monopterus albus (Zuiew), is an important aquaculture fish in many Asian countries. Productivity, however, is limited by low fecundity as a result of sex reversal of female juveniles of this fish. This study was conducted to investigate the effects of estradiol valerate on the sex reversal process of this fish by determining sex changes of initial 2‐yr‐old female eels (26.5 ± 2.6 cm, 21.9 ± 2.1 g) treated with three concentrations of estradiol valerate: 0 mg/kg (Control, Group A), 10 mg/kg (Group B), and 50 mg/kg (Group C). In Group A, sex reversal took place with significantly higher percentage of sex change: about 45% of female eels to intersexes and males. Only about 22% of female eels changed to intersexes and males in Group B, but no sex reversal occurred in Group C during the experimental period. The result also indicated that the gonadal development and the concentrations of serum estradiol (E₂) and testosterone (T) varied significantly with different concentrations of dietary estradiol valerate. Serum T significantly reduced but serum E₂ significantly increased in Group C compared to the control Group A. The results demonstrated that estradiol valerate affected the secretion of sex steroid hormones in rice field eels and thus inhibited the sex reversal process at a low concentration (10 mg/kg) or stopped the sex reversal process at a high concentration (50 mg/kg) of estradiol valerate. These results suggest that a higher yield of mature female eels could be achieved by treatments with estradiol valerate, thus enhancing the fecundity of this rice field eel.     

Effects of the estrogen mimic genistein as a dietary component on sex differentiation and ethoxyresorufin-O-deethylase (EROD) activity in channel catfish (<Emphasis Type="Italic">Ictalurus punctatus</Emphasis>)

A number of aquaculture species, including channel catfish Ictalurus punctatus, are fed high proportions of soybean meal in their diet. We have investigated the potential for the most common phytoestrogen in soybean meal to alter phenotypic sex during sexual differentiation in channel catfish. Channel catfish were fed four dietary concentrations of the phytoestrogen genistein (0, 2, 4, and 8 mg g⁻¹) to determine its effect on gonadal sex differentiation. The four treatment diets were fed to sexually undifferentiated channel catfish between 5 and 140 days post hatch (dph) and between 60 and 150 dph. Phenotypic sex was determined by histological examination of the gonads. Ethoxyresorufin-O-deethylase activity was not significantly different among the treatment and control groups. Phenotypic sex was significantly dependant on dietary phytoestrogen concentration (P = 0.01). Additionally, logistic regression showed a significant relation between genistein concentration in the diet and gonadal sex (P = 0.02). Intersex individuals were present at all treatment concentrations, with increasing proportions of intersex fish as the genistein concentration increased for individuals fed treated diets between 5 and 140 dph. Increased proportions of phenotypically male individuals resulted from chronic dietary exposure to the estrogen mimic genistein. There were no significant differences in the proportions of males and females between feed treatment durations. These findings establish that dietary concentrations of genistein can alter sex ratios in cultured channel catfish populations and demonstrates the need to further understand the actions of this and other prominent phytoestrogens in aquaculture species.     

Effect of 17 α-methyltestosterone on gonadal differentiation in pikeperch, Stizostedion lucioperca L.

Morphological and histological studies demonstrated that 17 α-methyltestosterone (MT) affects sex differentiation and can be used to control the phenotypic sex of pikeperch. Stizostedion lucioperca L. Treatment (for 21 days) of pikeperch (initially 2.2 g wet weight) with MT at 30 mg kg^-1 diet induced germ cells inversion in approximately 46.67% of individuals (although 96.67% of the fish were classified as males). An increase in treatment duration (60 and 90 mg kg^-1) increased the percentage of female, intersex and sterile fish. Slower growth rates of all the fish treated with MT in comparison to the control groups were demonstrated. However, no significant differences in conditions and mortalities between the MT treated fish and controls were observed.     

Artificial sex reversal of white grouper (Epinephelus aeneus) utilizing aromatase inhibitor (Fadrozole)

The white grouper is a desirable aquaculture species that adapts to captivity, grows well and commands a high market price. However, little is known about reproductive biology or control of sex reversal of this protogynous hermaphrodite. In this study, female white groupers were implanted with one dose of 17α‐methyltestosterone (10 mg/kg body weight [BW], MT) and two doses of aromatase inhibitor, fadrozole (1 and 3 mg/kg BW, FD1 and FD3) once a month for 4 months (April–July). At the start of the study, the fish had gonads full of oocytes compared to the end of the experiment when the control group mature oocytes compared to the experimental groups MT, FD1 and FD3 that exhibited different stages of testicular tissue. Plasma levels of testosterone were significantly highest in the FD3 group and the highest 11‐Ketotestosterone levels were observed in the MT group. Plasma levels of oestradiol (E₂) were significantly lower in the FD implanted groups, compared to initial individuals and control groups. The use of aromatase inhibitor, FD for sex reversal both gives further insight into the mechanisms controlling sex differentiation and provides an alternative to steroid treatment.     

A non‐paradoxical dose response to 17α‐methyltestosterone by Nile tilapia Oreochromis niloticus (L.): effects on the sex ratio,growth and gonadal development

Commercial tilapia production is dependent on monosex culture, commonly obtained through the inclusion of an androgen in the diet for a brief period soon after hatch. To determine a minimum effective dose and identify the problems associated with over‐dosing, Nile tilapia Oreochromis niloticus fry were fed diets containing methyltestosterone (MT) at rates up to 1200 mg kg^?1 of diet for 28 days. The minimum effective dose for ≥95% males was 14 mg MT kg^?1 diet. Percent phenotypic males increased as the rate increased from 3.75 (80%) to 30 mg kg^?1 MT (99%). Methyltestosterone given at rates of 120 mg kg^?1 or more reduced efficacy but did not result in a reduced frequency of males relative to that of non‐treated fish. The term ‘paradoxical feminization’ does not adequately describe the observed sex ratios, where no fish were feminized but the efficacy of MT at high doses to masculinize females was reduced. At 1200 mg MT kg^?1, the frequency of females (48 ± 1%) was not different from that in the non‐treated population. The mechanism for the reduced efficacy is not clear and is not adequately explained as an aromatization of androgen to oestrogen response.     

Effect of Astaxanthin from Xanthophyllomyces dendrorhous on the Pigmentation of Goldfish, Carassius auratus

Two experiments were conducted to evaluate the addition of astaxanthin from red yeast, Xanthophyllomyces dendrorhous, in the diets of goldfish, Carassius auratus. The first was designed to investigate the distribution of pigments in different tissues of goldfish and the effect of astaxanthin in the diet. The carotenoid concentration of tissues was not homogenous. The content of pigments in fish caudal fin was the highest followed by those of scales and head. Flesh had the least carotenoid deposition. Fish fed the diet containing 60 mg/kg astaxanthin had increased concentration of pigment in its head (22.6%), scales (45.5%), flesh (31.0%), and fin (21.2%), compared to fish fed basal diet (P < 0.05). Sixty parts per million astaxanthin had no effect on the weight gain and survival rate. High‐performance liquid chromatography analysis showed astaxanthin in its esterified form in goldfish. The second experiment was aimed at determining the dietary level of astaxanthin that improved color of goldfish. Goldfish were fed the same diet supplemented with 0, 10, 20, 40, 60, and 80 mg yeast astaxanthin/kg for 60 d. The deposition of carotenoids in goldfish fed diets supplemented with astaxanthin increased significantly (P < 0.05) after 15 d of feeding compared to that of the fish fed the diet without astaxanthin, but the effect of dosage of astaxanthin in the diets on the color of goldfish was not completely evident until Day 60 (P < 0.05). During the period of 15–45 d, the deposition of pigments in fish did not increase significantly (P > 0.05) in any treatment with the exception of the diet with 40 mg yeast astaxanthin/kg.     

Effects of low dietary protein level on serum oestradiol,testosterone and sex reversal in rice field eel,Monopterus albus (Zuiew)

We investigated the effects of low dietary protein in isocaloric diets on sex reversal of Monopterus albus by evaluating the oestradiol (E₂) and testosterone (T) concentrations, gonadosomatic index (GSI), sex ratio and gonad structure at the histological level. Fish (9.50 ± 1.50 g average initial weight; n=3 per group) were fed with five practical diets containing 100, 150, 200, 250 or 400 g kg^?1 crude protein to apparent satiation for 15 months. Serum E₂ and T concentrations were determined by radioimmunoassays. E₂ concentrations and GSI significantly increased while T concentrations decreased as the dietary protein level was raised. Fish fed 400 g kg^?1 of dietary protein had significantly higher E₂ concentrations and GSI than those fed with lower dietary protein levels. The T concentrations of fish fed 100 g kg^?1 of dietary protein was significantly higher than that of fish fed higher dietary protein levels. The shift of sex ratio towards more male and intersex fish was observed with decreasing dietary protein levels. Therefore, low dietary protein level may promote sex change from female to male in M. albus. This study provides important information for successful reproductive management and may be exploited for aquaculture of this species.     

Use of Fermented Fisheries By-products and Soybean Curd Residues Mixture as a Fish Meal Replacer in Diets of Juvenile Olive Flounder, Paralichthys olivaceus

A 10‐wk feeding trial was conducted to evaluate the potential use of fermented fisheries by‐products and soybean curd residues mixture (FFSM) as a partial replacement for fish meal (FM) in the diet of juvenile olive flounder, Paralichthys olivaceus. Five experimental diets were formulated with FFSM replacing 0, 15, 30, 45, and 60% of the FM protein (FFSM₀, FFSM₁₅, FFSM₃₀, FFSM₄₅, and FFSM₆₀, respectively). Juvenile olive flounder averaging 5.99 ± 0.08 g (mean ± SD) were randomly distributed into aquaria at 15 fish/aquarium, with three replicate aquaria for each experimental diet. Weight gain (WG) of fish fed FFSM₀, FFSM₁₅, and FFSM₃₀ was significantly higher than that of fish fed FFSM₄₅ and FFSM₆₀ (P < 0.05). Also, WG of fish fed FFSM₄₅ was significantly higher than that of fish fed FFSM₆₀ (P < 0.05). There were no significant differences in WG among fish fed FFSM₀, FFSM₁₅, and FFSM₃₀ (P > 0.05). Specific growth rate (SGR) of fish fed FFSM₁₅ was significantly higher than that of fish fed FFSM₄₅ and FFSM₆₀ (P < 0.05). Also, SGR of fish fed FFSM₀, FFSM₁₅, FFSM₃₀, and FFSM₄₅ was significantly higher than that of fish fed FFSM₆₀ (P < 0.05). There were no significant differences in SGR among fish fed FFSM₀, FFSM₁₅, and FFSM₃₀ and among those fed FFSM₀, FFSM₃₀, and FFSM₄₅ (P > 0.05). Feed efficiency (FE) and protein efficiency ratio (PER) of fish fed FFSM₆₀ were significantly lower than those of fish fed FFSM₀, FFSM₁₅, FFSM₃₀, and FFSM₄₅ (P < 0.05); however, there were no significant differences in FE and PER among fish fed FFSM₀, FFSM₁₅, FFSM₃₀, and FFSM₄₅. Hepatosomatic index of fish fed FFSM₀, FFSM₁₅, and FFSM₃₀ was significantly higher than that of fish fed FFSM₆₀ (P < 0.05); however, there were no significant differences among fish fed FFSM₀, FFSM₁₅, FFSM₃₀, and FFSM₄₅ and among those fed FFSM₄₅ and FFSM₆₀. No significant differences were observed in condition factor and survival rate among all dietary groups tested. The whole‐body proximate composition averaged 75.0 (% dry matter basis [DM]), 8.66 (% DM), 16.38 (% DM), and 76.1%, for crude protein, crude lipid, ash, and moisture, respectively. Based on growth performance, the FFSM could replace up to 30% FM protein by the ANOVA test; however, broken‐line model analysis indicated 28.7% as an optimum replacement level in juvenile olive flounder diets.     

Evaluation of Stocking Density during Second‐Year Growth of Largemouth Bass,Micropterus salmoides,Raised Indoors in a Recirculating Aquaculture System

Largemouth bass (LMB), Micropterus salmoides, are a highly desirable food fish especially among Asian populations in large cities throughout North America. The primary production method for food‐size LMB (>500 g) has been outdoor ponds that require two growing seasons (18 mo). Indoor, controlled‐environment production using recirculating aquaculture system (RAS) technologies could potentially reduce the growout period by maintaining ideal temperatures year‐round. Researchers conducted a 26‐wk study to evaluate optimal stocking densities for growout of second‐year LMB to food‐fish size in an indoor RAS. LMB fingerlings (112.0 ± 38.0 g) were randomly stocked into nine 900‐L tanks to achieve densities of 30, 60, or 120 fish/m³ with three replicate tanks per density. The RAS consisted of a 3000‐L sump, ¼ hp pump, bead filter for solids removal, mixed‐moving‐bed biofilter for nitrification, and a 400‐watt ultraviolet light for sterilization. Fish were fed a commercially available floating diet (45% protein and 16% lipid) once daily to apparent satiation. At harvest, all fish were counted, individually weighed, and measured. Total biomass densities significantly increased (P ≤ 0.05) with stocking rate achieving 6.2, 13.2, and 22.9 kg/m³ for fish stocked at 20, 60, and 120 fish/m³, respectively. The stocking densities evaluated had no significant impact (P > 0.05) on survival, average harvest weight, or feed conversion ratio which averaged 92.9 ± 5.8%, 294.5 ± 21.1 g, and 1.8 ± 0.3, respectively. After approximately 6 mo of culture, LMB did not attain target weights of >500 g. Observed competition among fish likely resulted in large size variability and overall poor growth compared to second‐year growth in ponds. Additional research is needed to better assess the suitability of LMB for culture in RAS.     

Fishmeal replacement by soybean,rapeseed and cottonseed meals in hybrid sturgeon Acipenser baerii ♀ × Acipenser schrenckii ♂

A 12‐week feeding trial was conducted to evaluate the effects of replacing fishmeal (FM) with soybean meal (SBM), rapeseed meal (RM) and cottonseed meal (CSM) on growth, feed utilization and body composition of juvenile hybrid sturgeon Acipenser baerii ♀ × Acipenser schrenckii ♂ (initial body weight, 8.63 ± 0.24 g). Five isonitrogenous and isoenergetic diets were formulated as follows: a control diet (FM60) containing 600 g/kg FM and four other diets (FM45, FM30, FM15 and FM0 containing 450, 300, 150 and 0 g/kg FM, respectively) where protein from FM was substituted by a mixture of SBM, RM and CSM. Fish fed FM0 and FM15 had poorer growth performance, feed utilization, apparent digestibility coefficients of dry matter, protein, lipid and gross energy, and fed FM0 had poorer hepatosomatic index and survival compared with the fish fed FM60. The whole body lipid in fish fed FM0 was significantly higher than that in fish fed FM60 and FM15. This study indicates that 300 g/kg of FM can be replaced with a mixture of SBM, RM and CSM in the diet of juvenile hybrid sturgeon without compromising growth performance, feed utilization and body composition.     

Effects of Gender and Sex Hormones on Disease Susceptibility of Channel Catfish to Edwardsiella ictaluri

The use of monosex populations for aquaculture is becoming widely used for several species. The current studies determined if there were any differences between male and female channel catfish, Ictalurus punctatus, in disease susceptibility to Edwardsiella ictaluri, one of the most important pathogenic bacteria in catfish culture. Disease challenge experiments were carried out on fingerling channel catfish fed 17β‐estradiol or testosterone before the challenge, and on all male and on sibling all female fingerlings. All male populations were produced by mating YY males with normal XX females. Sibling females were produced by hormonally sex reversing a subpopulation of six of the all male families. Weight gain or specific growth rate did not differ in fish fed testosterone or estrogen. Fish fed the highest dose of estrogen (50 mg/kg) had a significant higher mortality (P < 0.05), while mortality was similar in catfish fed 10 and 50 mg/kg of testosterone compared to controls. There were no differences in mortality between sibling males and females. These data indicate no increased disease susceptibility to E. ictaluri between males and females or due to exogenous sex hormones. Production of all male catfish for culture can proceed without concern for disease susceptibility to E. ictaluri.     

Effect of 17β‐oestradiol on the sex ratio of tambaqui,Colossoma macropomum

The tambaqui Colossoma macropomum is the most important native fish in Brazilian aquaculture. Females are almost 20% heavier than males and therefore are more profitable. Based on this information, we tested four different concentrations (20, 40, 80, and 120 mg/kg diet) of oestradiol (E₂) offered during 6 weeks to tambaqui larvae and analysed their efficiency in producing female monosex batches of the species. The study was performed in two independent tests, using different genetic backgrounds (broodstocks). All treatments increased the percentage of females in the population, but only the highest E₂ dose was “free” of males in both tests. All treated groups contained intersex individuals (when sex inversion is not complete). Plasmatic E₂ concentration was similar between treated and non‐treated fish 60 days after the treatment in fish treated with 20, 40, and 80 mg E₂/kg diet. However, tambaqui treated with a 120 mg E₂/kg diet showed lower E₂ plasma concentration in comparison with the control group. Last, we chlorinated the water to ensure the environmental integrity of the study. Three days after chlorination, the water was completely free of any oestradiol residue (analysed by high‐performance liquid chromatography).     

Nano zinc vis‐à‐vis inorganic Zinc as feed additives: Effects on growth,activity of hepatic enzymes and non‐specific immunity in rohu,Labeo rohita (Hamilton) fingerlings

The effects of dietary administration of inorganic zinc (zinc sulphate, ZnSO₄) and nano zinc (zinc oxide nanoparticles, ZnO‐NP) were evaluated in rohu, Labeo rohita fingerlings. Fish were fed with a basal diet (Control) supplemented with ZnSO₄ (T1, T2 and T3) and ZnO‐NP (T4, T5 and T6) at 10, 20 and 30 mg/kg, respectively, for a duration of 45 days. The results revealed that fish fed diet containing 20 mg ZnO‐NP per kg (T5) had the highest weight gain and specific growth rate (SGR, % per day), which was significantly different (p < .05) from the other experimental diets. Significantly (p < .05), higher activities of the digestive and metabolic enzymes were recorded in the fish fed ZnO‐NP containing diets as compared to the diets containing inorganic Zn or control diet. The maximum serum glucose and protein levels were noted in fish reared on diet T5. Both SGOT and SGPT activities were significantly increased in fish fed Zn‐supplemented diets (T1 to T6), as compared to the control group. Similarly, innate immune parameters were improved with feeding Zn incorporated diets. The highest phagocytic (40.74 ± 0.65%) and respiratory burst (0.33 ± 0.001, OD 630nm) activities were recorded in the fish fed diet containing ZnO‐NPs at 20 mg/kg (T5). The maximum superoxide production and serum peroxidase activity were detected in the fish fed T5 and T6 diets. Overall, results indicated that short‐duration feeding (≤45 days) of dietary ZnO‐NP (20 mg/kg) improved growth, enzyme activity, serum biochemical parameters and immune function in rohu fingerlings.     

Efficacy of 17 α‐methyl testosterone and letrozole on sex reversal of protogynous grouper,Epinephelus tauvina (Forskal, 1775) and spawning performance of sex‐reversed males

This study aimed to test the efficacy of 17 α‐methyl testosterone (17 α‐MT) alone and in combination with letrozole, an aromatase inhibitor, for the induction of sex reversal in protogynous greasy grouper, Epinephelus tauvina. Further, the long‐lasting effects of these treatments and spawning performance of sex‐reversed males were also investigated. Greasy grouper with oocytes in the perinucleolus stage were implanted with 5 mg 17 α‐MT kg^?1 body weight (T₁), 5 mg 17 α‐MT and 0.2 mg letrozole kg^?1 body weight (T₂) and 5 mg 17 α‐MT with 0.4 mg letrozole kg^?1 body weight (T₃) and no androgens/enzyme inhibitor implanted (C). The 17 α‐MT alone and in combination of letrozole‐induced sex reversal in greasy grouper, whereas untreated control fish (C) showed normal ovarian development. However, T₂ and T₃ group showed 100% sex reversal and completion of spermatogenesis up to functional male phase in 2 and 3 months, respectively, whereas T₁ group resulted in only 66.67% functional male with motile spermatozoa after 4 months. Sex‐reversed males successfully fertilized the eggs during induced spawning. There were significant differences on fertilization and hatching rates between T₂ group (79.00 ± 4.36%; 77.67 ± 2.87%, respectively) and T₁ group (57.67 ± 3.17%; 63.87 ± 2.91%, respectively). The result suggested that 17 α‐MT (5.0 mg kg^?1 BW) in combination with letrozole (0.2 mg kg^?1 BW) has the potential to produce 100% sex‐reversed male in short period in greasy grouper, which might greatly help in seed production of greasy grouper.     

Effect of fluoxymesterone on sex ratio and growth of Nile tilapia, Oreochromis niloticus (L.)

The androgenic and anabolic potential of fluoxymesterone (FM) was evaluated by incorporating the hormone into the feed of Nile tilapia, Oreochromis niloticus(L.) fry. Phenotypic all-male populations were produced when FM was given at 1, 5 and 25mg/kg of feed. Fry fed methyltestosterone (MT) at 60 mg/kg of feed and 0-2 mg of FM per kg of feed had a sex ratio of 97-7% and 87-3% phenotypic males. No positive anabolic effect was evident in response to adding FM or MT to the feed at the end of the 28-day treatment period or after an additional 6 weeks of growth without hormone. Growth was less for fry which received 25 mg/kg of FM compared to those receiving lesser rates of FM, 60 mg/kg MT, and controls.     

Increased androgen receptor expression in muscle tissue contributing to growth increase in androgen-treated Nile tilapia

The aim of this study was to investigate the molecular mechanism behind androgen-induced sex reversal and growth increase in Nile tilapia. Three-day-old mixed-sex tilapia juveniles were treated with differential dose (0, 5, 10, 20, 30 mg/kg diet) and duration (0, 15, 30, 45, 60 days) regimes of 17α-methyltestosterone. Treatment regimes 10, 20, 30 mg/kg-30, 45, 60 days showed ~95% males, while 0 mg/kg-0 days (control) showed ~50% males (P < 0.01). Next, tilapia was cultured for 6 months in cistern and pond culture systems with 17α-methyltestosterone-treated diet (10 mg/kg) for three different durations: 0 days (control), 30 days (30-day-treated), and 180 days (throughout-treated). Fish in pond culture showed significantly higher (P < 0.05) final weight compared with tilapia in cistern culture (235.76, 156.82 g, respectively). Both 30-day-treated and throughout-treated fish showed significantly higher (P < 0.05) final weight, length, daily weight gain, specific growth rate, and muscle protein content compared with control fish. The androgen receptor β mRNA and protein expression levels in both 30-day-treated and throughout-treated fish were significantly higher (~twofolds, P < 0.05) compared with hormone-untreated control males. However, there was not much difference for all these parameters among the two hormone-treated groups. This higher growth probably results from an androgen-induced increased ‘androgen-androgen receptor’ mediated anabolic pathway. Serum testosterone concentration of 30-day-treated fish after 6 months was similar to that of control males (0.9 ng/ml). Moreover, culture of 17α-methyltestosterone-treated monosex tilapia was found beneficial than hormone-untreated mixed-sex tilapia culture for maintenance of natural fish diversity in indigenous water bodies.     

Growth,nutrient utilization,oxidative condition,and element composition of juvenile red sea bream <Emphasis Type="Italic">Pagrus major</Emphasis> fed with fermented soybean meal and scallop by-product blend as fishmeal replacement

A feeding trial was conducted to evaluate the effect of fermented soybean meal and scallop by-product blend (3:2) (FP) on the performance of juvenile red sea bream. Five isocaloric diets were prepared by replacing 0% (FP0), 15% (FP15), 30% (FP30), 45% (FP45), and 60% (FP60) fishmeal (FM) protein with FP, respectively. Triplicate groups of fish (initial mean weight 2.83 g) were fed the test diets for 45 days in a flowthrough seawater system. The results demonstrated that growth rates of fish fed FP0, FP15, and FP30 were similar, and significantly higher (P < 0.05) than those of FP45 and FP60. Nutrient utilization was significantly lower in FP60, with no differences found among the other groups. Dietary heavy-metal contents were affected by inclusion of FP, impacting on whole-body heavy-metal contents. In terms of oxidative stress, fish fed the FP30 diet were in the best condition, since this fish group showed the least oxidative-stressed condition as well as the highest tolerance against oxidation. In conclusion, the approach of utilizing this fermented mixture is promising and it could replace at least 30% FM protein in red sea bream diet without negative effects on performance, body composition or health of fish.