Effects of oestradiol-17β or 17α-methyltestosterone administration on gonadal differentiation of largemouth bass Micropterus salmoides (Lacepède)

Monosex populations can be a valuable management tool in culture of larger size largemouth bass (>400 g). In this study, we investigated the effective mode and duration of oestrogen and androgen administrations to produce monosex largemouth bass populations. The experiment consisted of nine treatments. In oral administration groups, we fed 40-day-old fry either 200 mg of an oestradiol-17β (E₂) kg⁻¹ diet or 60 mg of a 17α-methyltestosterone (MT) kg⁻¹ diet for 30, 45 or 60 days. In bath treatments, we immersed fry in a 1 mg MT L⁻¹ solution for 5 h a day on three or six occasions. For control treatment, we fed fry an ethanol-treated diet for 45 days. The frequency of females in the control group was 53.1%. Oral administration of E₂ at all durations resulted in slight increases in the frequency of females (59.8–70.5%). Both modes of androgen administration at all durations were ineffective in altering phenotypic sex. The experimental results of our study indicated that male differentiation passed the point of being completely and functionally influenced by exogenous oestrogens, while female differentiation had already taken place and was no longer responsive to exogenous androgens in 40-day-old (33.5 mm) largemouth bass fry.     

Multigenerational effects of 17β-estradiol and nonylphenol on euryhaline cladoceran <Emphasis Type="Italic">Diaphanosoma celebensis</Emphasis>

ABSTRACT:     The effects of parental exposure to 17β-estradiol (E2) and 4-nonylphenol (4-NP) on life history parameters of three successive generations of the euryhaline cladoceran Diaphanosoma celebensis were assessed under laboratory conditions. Less than 24-h-old neonates (P) were exposed to five sublethal concentrations of E2 (0.1, 1, 10, 100 and 1000 μg/L) and 4-NP (0.01, 0.1, 1, 10 and 50 μg/L) at 25°C. Age at first reproduction, reproductive period, fecundity and lifespan were investigated. Successive generations (F₁–F₃) were monitored further in the absence of toxicants. Results showed that cladocerans exposed to 10–1000 μg/L E2 produced more neonates at a younger age compared to the control. The same effects were also observed in the F₁ and F₂ but ceased in F₃. Cladocerans exposed to 1 μg/L 4-NP also produced significantly more neonates compared to the control, but this effect was not found in successive generations. The results suggest that vertebrate hormone can modify the reproduction of D. celebensis , and the effects are multigenerational.     

Annual changes in ovarian development and plasma estradiol-17β level in reared female common Japanese conger, <Emphasis Type="Italic">Conger myriaster</Emphasis>

ABSTRACT:   Annual changes in the gonadosomatic index (GSI), oocyte diameter, gonadal histology and plasma estradiol-17β (E₂) levels were investigated in female common Japanese conger Conger myriaster in captivity. Juveniles were caught in September 1999 and reared in seawater at temperatures ranging from 10–20°C for 3 years. All fish were immature when captured in September 1999. GSI and oocyte diameter increased from October 2000, peaked between summer and autumn 2001, and bottomed-out in winter 2001. Plasma E₂ level also increased from October 2000, but remained high. The ovarian developmental stage was at the peri-nucleolus stage or the oil droplet stage until September 2000. Vitellogenesis started in October 2000 and oocytes progressed to the tertiary yolk globule stage by summer 2001. However, vitellogenic oocytes regressed in all females after autumn 2001. The neogenetic oocytes began to increase after November 2001 and ovarian development progressed in 2002 as they did in 2001, although maximum GSI in 2002 was half its 2001 value. These data indicate that ovarian development in the common Japanese conger has an annual periodicity, and that these congers may be able to spawn in multiple years under rearing condition.     

Effect of Genistein on the Growth and Reproductive Function of Male and Female Yellow Perch Perca flavescens

We studied the effect of genistein, a weak estrogenic compound found in soybean products, on the growth and reproductive development of yellow perch Perca flavescens . Four diets were prepared: control, estradiol-17β (E₂) at 10 μg/g diet (E10), and genistein at 7.5 and 0.75 mg/g diet (G7.5 and G0.75). Fish (initial weight = 13–15.5 g and initial total length = 105–111 mm) were fed to excess for 63 d. The E10 diet promoted weight gain in yellow perch of both sexes, whereas the G7.5 diet decreased weight gain in females. The growth of the G0.75 group was not different from either the E10 group or the control group. Among females, fish fed the E10 diet had the lowest plasma concentration of E₂ 36 h after the last feeding of the study. The plasma concentration of E₂ did not differ among the males from the four treatments. The E10-treated fish of both sexes had increased plasma concentration of alkali-labile phosphoprotein phosphorous (ALPP) in both sexes, indicating that vitellogenesis had been induced. Neither genistein diet increased plasma (ALPP) concentration. Male but not female yellow perch fed the E10 diet had significantly lower gonadosomatic indices compared to control and genistein groups. These results suggest that genistein may have a positive effect on growth in yellow perch, but no apparent estrogenic effects on reproductive function.     

Morphological sex change upon treatment by endocrine modulators in meiogynogenetic tench (Tinca tinca L.)

Exogenous steroids alter sex differentiation in fish substantially. In the present study we have evaluated the effects of 17α-methyltestosterone (MT) and oestrogen receptor antagonist Tamoxifen (TA) on gonadal development and skewness of the sex ratio in all-female tench juveniles. In the first two experiments, sexually undifferentiated juveniles were orally treated with three doses of MT and TA (50, 100 and 150 mg kg⁻¹). Both the treatments resulted in a moderate dose-dependent masculinization, with neomale production ranging from 17% (50 mg kg⁻¹) to 26% (150 mg kg⁻¹) for the MT only treatment, and from 0% (50 mg kg⁻¹) to 27% (100 mg kg⁻¹) only for the TA treatment respectively. In the third experiment treatment of sexually differentiated tench females with single steroid treatments or combinations of the two resulted in populations composed of females and intersex individuals. The significantly highest occurrence of intersex individuals (45.5%) was found in the group subjected to combine treatment of MT+TA (150+200 mg kg⁻¹). No masculinization effect of the single or the combined treatment occurred. It can be concluded that oral treatment with MT or TA only slightly modifies the normal process of sex differentiation in gynogenetic tench juvenile, but treatment with the above-mentioned combinations has a highly significant potential to skew the sex ratio in sexually differentiated tench females. However, from an applied point of view, the treatment procedure will need optimization before use at a commercial level.     

Seasonality of serum levels of vitellogenin in male Japanese whiting, Sillago japonica, reared under natural temperature and photoperiod

ABSTRACT:   Because blood vitellogenin (Vg) has been considered a biomarker for environmental estrogens, the basal levels of Vg and 17β-estradiol (E₂) were determined in male Japanese whiting reared under natural conditions. Serum levels of Vg and E₂ were measured and gonadal development was assessed by gonadosomatic index (GSI) and histological observation in 8–10 male fish at monthly intervals throughout the annual reproductive cycle. Serum E₂ was <60 pg/mL throughout the study period. In contrast, serum Vg exhibited seasonal changes: serum levels of Vg gradually increased from April to May (mean 63 ± 13 ng/mL and 124 ± 48 ng/mL in April and May, respectively), and then reached a peak value (mean 352 ± 68 ng/mL) in June. Thereafter, serum Vg gradually decreased, reaching undetectable levels (<50 ng/mL) in October. Serum levels of Vg tended to increase in the male fish in which the GSI was >1%. Histological observation revealed that testes in such male fish were in active spermatogenesis and then all of the testes of male fish in which serum Vg decreased to ND levels were regressed. These results suggest that Vg productive potency (sensitivity to estrogens) may increase in the spermatogenic stage, resulting in production of Vg in response to very low levels of natural or xenobiotic estrogens.     

Dose-dependent influences of dietary β-1,3-glucan on innate immunity and disease resistance of hybrid striped bass Morone chrysops×Morone saxatilis

To investigate potential use of dietary β-1,3-glucan for health management of hybrid striped bass, juvenile fish were fed diets supplemented with yeast glucan (MacroGuard^®) at 0.05%, 0.1% or 0.2% of diet for 4 weeks, followed by immune response assays and a bath challenge with Streptococcus iniae . Dietary glucan significantly ( P <0.05) enhanced neutrophil oxidative radical production, and fish fed 0.1% glucan had a significant ( P <0.05) reduction in mortality (10%) after bacterial challenge compared with fish fed the control diet (46.7%). However, accumulative mortality of fish fed 0.2% glucan was not significantly different from that of fish fed the control diet. To further elucidate this observation, macrophages from sub-adult hybrid striped bass were isolated and cultured in L-15 medium with 10% foetal calf serum and penicillin/streptomycin supplemented with 0.2, 0.5, 1, 2, 5, 20 and 100 μg soluble glucan (MacroGuard^®) mL⁻¹ for 24 and 48 h. Intracellular superoxide anion production was significantly ( P <0.001) increased by 0.5 μg glucan mL⁻¹, but significantly ( P <0.001) suppressed by doses >5 μg glucan mL⁻¹. It is concluded that dietary yeast glucan has potential for use in diet formulations of hybrid striped bass to limit the adverse effects of S. iniae , but dosage should be an important consideration in administration.     

Natural abundance of 15N and 13C in fish tissues and the use of stable isotopes as dietary protein tracers in rainbow trout and gilthead sea bream

For developing efficient diets, two sets of experiments examined whether the use and allocation of dietary protein can be traced by labelling with stable isotopes (¹⁵N and ¹³C) in two culture fish ( Oncorhynchus mykiss and Sparus aurata) . In the first experiment, natural abundance and tissue distribution of these isotopes were determined, by measuring the δ¹³C and δ¹⁵N values by isotopic ratio mass spectrometry, in fingerlings (14–17 g) adapted to diets differing in the percentage of fish meal replacement by plant protein sources. For both species, δ¹⁵N and δ¹³C were greater in tissues with higher protein and lower lipid content. Delta ¹⁵N of diets and tissues decreased as replacement increased, suggesting δ¹⁵N can be used as a marker for dietary protein origin. The ¹⁵N fractionation (δ¹⁵N fish − δ¹⁵N diet) differed between groups, and could thus be used to indicate protein catabolism. In the second experiment, fish (75–90 g) of each species ingested a diet enriched with ¹⁵N-protein (10 g kg⁻¹ diet) and ¹³C-protein (30 g kg⁻¹ diet). These proportions were suitable for determining that the delta values of tissue components were high enough above natural levels to allow protein allocation to be traced at 11 and 24 h after feeding, and revealed clear metabolic differences between species.     

Influence of α-tocopherol acetate on the short- and long-term storage properties of fillets from Atlantic salmon Salmo salar fed a high lipid diet

During refrigeration, lipid oxidation is a major factor contributing to post-mortem deterioration of flesh quality. Polyunsaturated fatty acids (PUFA), especially n -3 PUFA, are present in high concentration in fish tissues, and in oils used in diets, and are readily susceptible to peroxidation. α-Tocopherol (AT) can reduce tissue lipid peroxidation in vivo and post mortem. The effect of increasing the tissue level of AT by dietary supplementation of α-tocopherol acetate (ATA) was therefore investigated. Commercial salmon diets C, M and H, high in lipids, containing 184, 573 and 865 mg ATA kg⁻¹ diet DM (dry matter) were fed to 18 fish per treatment. Dietary AT: PUFA ratios were 2.0, 6.3, and 9.5 mg g⁻¹ for diets C, M and H, respectively. Fish (mean initial live weight 630 g) were slaughtered after 50 and 78 days of feeding. Fillet samples were analysed fresh or after storage at 4 °C for 12 days and –20 °C for 12 months. Lipid oxidation was measured using the thiobarbituric acid test. Colour score, but not carotenoid content, of fillets was significantly higher between 6 and 12 days of fresh storage in fish fed diets M and H compared with those fed diet C. Colour score, carotenoid content and ΑΤ content decreased and the content of lipid oxidation products increased following storage of fillets at –20 °C for up to 12 months, although lipid oxidation was always significantly lower in fish fed diets M and H.     

Dietary vitamin E requirement of hybrid striped bass (Morone chrysops female × M. saxatilis male)

This study was conducted to determine the dietary vitamin E requirement of juvenile hybrid striped bass ( Morone chrysops female ×  Morone saxatilis male). Semi-purified diets supplemented with 0.2 mg Se kg⁻¹ from Na₂SeO₃ and either 0 (basal), 10, 20, 40, 60, or 80 mg vitamin E kg⁻¹ as  DL -α-tocopheryl acetate were fed to hybrid striped bass initially averaging 1.8 ± 0.1 g (mean ± SD) for 12 weeks. Fish fed the basal diet, which contained 5.8 mg α-tocopherol kg⁻¹ dry weight, were darker in colour and had reduced weight gain, as well as generally reduced haematocrit values compared with fish fed diets supplemented with vitamin E. In addition, fish fed diets containing less than 20 mg supplemental vitamin E kg⁻¹ had significantly ( P  < 0.05) reduced weight gain and feed efficiency compared with those fed diets supplemented with vitamin E at 20–80 mg kg⁻¹. Dietary supplementation of vitamin E caused incremental increases in the concentration of α-tocopherol in both plasma and liver tissues. However, hybrid striped bass fed graded levels of vitamin E did not exhibit a dose response in terms of ascorbic acid-stimulated lipid peroxidation of hepatic microsomes. Regression analysis of weight gain data using the broken-line model indicated a minimum vitamin E requirement ( ±  SE) of 28 ( ±  3) mg kg⁻¹ dry diet. Based on these data, the dietary vitamin E requirement of hybrid striped bass appears to be similar to that determined for other fish species.     

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.     

Effects of Natural EstradioI-17β and Synthetic 17α- Ethynylestradiol on Direct Feminization of European Sea Bass Dicentrarchus labrax

To produce a monosex female population of European sea bass Dicentrarchus labrax, fry were fed dry diets containing dosages of 12.5, 25, and 50 mg/kg food of either the natural estrogen estradiol-170β(E₂) or the synthetic estrogen 17α-ethynylestradiol (EE₂) for 60 d starting at 88 d post-hatch (dph). A complete feminization (100%) was achieved in all E₂-treated groups at the age of 11 mo (330 dph). All affected fish had ovaries similar in size and histological structure to those of control females. In the E₂-treated groups, feminized fish were heavier and longer than untreated controls (males and females combined). In control groups females exhibited significantly higher body weight and total length than males. Untreated females from control groups and females from the group treated with E₂ at 12.5 mg/kg food had similar body weight, suggesting that in sea bass growth is related to phenotypic sex. In the Entreated groups, survival rates were similar to those of the control fish. A relatively high percentage of females was obtained in the EE₂-treated groups (from 38.6 to 96.5%). However, the gonadal development in these fish was significantly suppressed and a dose-dependent reduction of gonadal sizes was evident. Treatments with the EE₂ (12-5, 25, and 50 mg/kg food) resulted in many fish having abnormal (2.9-5.4-39.8%, respectively) and sterile (0.6-6.0-21.6%, respectively) gonads. Effects also included significantly lower weight and shorter length when compared with controls. Furthermore, fish fed with EE₂ at the dosage of 50 mg/kg food had high mortality rate. A simple protocol was developed for the complete feminization in sea bass in which the fry (80-100 dph) were fed to satiation two times daily with a diet containing 12.5 me of E₂/ks food for a period of 60 d.     

Nutritional evaluation of waste date fruit as partial substitute for soybean meal in practical diets of juvenile Nile tilapia, Oreochromis niloticus L.

The potential of waste date meal (WDM; low-quality date palm, Phoenix dactylifera L.) as a carbohydrate source in formulated diets for Nile tilapia was evaluated. Four isocaloric-practical diets (15.7 kJ g⁻¹) were formulated incorporating WDM at 0, 100, 200 and 300 g kg⁻¹ levels as partial substitutes for soybean meal (SBM). These were designated D₀ [284 g crude protein (CP) and 383 g carbohydrate (CHO) kg⁻¹ diet], D₁ (279 g CP and 446 g CHO kg⁻¹ diet), D₂ (207 g CP and 495 g CHO kg⁻¹ diet) and D₃ (175 g CP and 578 g CHO kg⁻¹ diet). Each diet was fed to three replicate groups of 30 fish [20.20 ± 0.09 g (±SE)] for 75 days. No feed-related mortality was observed during the entire experimental period. Final body weight (FBW) and specific growth rate (SGR) in the different treatments were statistically not significantly different ( P  > 0.05). Protein efficiency rate (PER) was lowest in diet D₀ and increased with decrease of SBM content (D₁–D₃). A significant increase in whole body lipid content was recorded in fish fed diets D₂ and D₃. Results showed that WDM could be a substitute for SBM up to 300 g kg⁻¹ in practical Nile tilapia diets without compromising growth.     

Precocious sex change and spermatogenesis in the underyearling Malabar grouper Epinephelus malabaricus by androgen treatment

The Malabar grouper Epinephelus malabaricus is an important candidate species for commercial aquaculture in tropical and subtropical areas. In nature, this species requires more than 10 years to change sex from female to male and have active spermatogenic tissues in the testis. Thus, it is essential to find a means of producing sperm for seed production. This is the first report of artificial sex change in underyearling E. malabaricus . Female E. malabaricus with immature ovaries at 144 days post-hatch (DPH) were fed a diet with 17α-methyltestosterone (MT) at 50 μg g⁻¹ diet for 6 months. Sex change occurred in most of the treated fish, which had testis with all stages of spermatogenic germ cells including spermatozoa. In contrast, most of the control fish had immature ovaries. These results, which reveal that germ cells in the underyearling grouper have the ability to produce spermatozoa in response to exogenous androgen, demonstrate that sex change can be artificially induced during ovarian development.     

A Mammalian Growth Hormone-Releasing Hormone Increases Serum Growth Hormone Levels and Somatic Growth at Suboptimal Temperatures in Tilapia

The effects of a mammalian growth hormone-releasing hormone (GHRH), PrebGRF(1–78)OH (bGHRH), on growth and serum growth hormone (GH) levels were investigated in tilapias Oreochromis mossambicus and O. niloticus × O. aureus . Fish were injected intramuscularly or implanted intramuscularly (Silastic or cholesterol implants) with distilled water, 0.1 μg/kg bGHRH, 1.0 μg/kg bGHRH, 10.0 μg/kg bGHRH, or 100.0 μg/kg bGHRH and compared to untreated controls, fish implanted with 60 mg/kg 17α-methyltestosterone (MT), or a combination of bGHRH concentrations plus either MT, 0.01 μg/kg of a thyroid hormone (T₃), or 0.01 μg/kg of a glucocorticoid (DEX). The bGHRH increased serum GH levels in tilapia maintained at suboptimal temperatures (18 C). Serum GH levels were highest (5.3–0.45 ng/mL) for fish injected with 10.0 μg/kg bGHRH. Fish implanted with a Silastic implant containing 10.0 μg/kg bGHRH had significantly higher (4.35–0.35 ng/mL) serum GH levels than those with an equivalent dosage in a cholesterol implant. The addition of MT, thyroid hormones, and glucocorticoids did not increase serum GH levels above those obtained for fish receiving bGHRH alone. Tilapia reared at suboptimal temperatures and implanted with 10.0 μg/kg and 100.0 μg/kg bGHRH had significantly greater increases in weight and length than control fish. Fish implanted with bGHRH, MT or bGHRH plus MT had significantly higher moisture and protein content, while fat and ash contents were significantly lower than controls or sham-implanted fish. Fish implanted with bGHRH or bGHRH plus MT had significantly higher gonadosomatic indices than fish implanted with MT alone, shams or non-treated controls. This study demonstrates that a mammalian GHRH stimulates release of GH, promotes somatic and gonadal growth and may affect reproductive performance in tilapia.     

Effect of Luteinising Hormone-Releasing Hormone Analogue and Human Chorionic Gonadotropin on Ovulation, Plasma and Ovarian Levels of Gonadal Steroids in Greenback Flounder Rhombosolea tapirina

Female greenback flounder Rhombosolea tapirina were treated with either des Gly¹⁰ [D-Ala⁶] LHRH ethylamide (LHRH-a) at 50 or 100 pg/kg intraperitoneal injection (ipi), LHRH-a cholesterol pellet (LHRH-a pellet) 100 μg/kg implanted intraperitoneally, or human chorionic gonadotropin (hCG) 1,000 IU/kg ipi. Treatment with hCG, LHRH-a (50 μg/kg) ipi and LHRH-a pellet increased the total number of ovulations above control levels. LHRH-a (100 μg/kg) ipi was not consistently more effective than the control and both LHRH-a (50 μg/kg) ipi and LHRH-a pellet induced more ovulations than LHRH-a (100 μg/kg) ipi. Of those fish that ovulated, most ovulated more than twice, and most ovulations occurred at daily intervals. Oocyte diameters increased and oocyte stage advanced significantly in response to all exogenous hormone treatments. This was accompanied by increases in plasma and ovarian levels of 17β-estradiol (E₂, and in most cases, plasma and ovarian levels of testosterone (T). Plasma and ovarian levels of 17,20β-dihydroxy-4-pregnen-3-one (17,20βP) were not consistently elevated in association with reproductive events.     

Comparison of in vitro vitellogenin synthesis among different nonylphenol products using primary cultures of tilapia hepatocytes

Effect of nonylphenol (NP) products from different companies on in vitro vitellogenin (VTG) synthesis was compared using tilapia ( Oreochromis mossambicus ) hepatocytes cultures. Addition of NP at a concentration of 10⁻³ M to the medium caused death of hepatocytes (NP-A and NP-B) and delay of monolayer formation (NP-C). No cell death was observed at a concentration of 10⁻⁴ M (NP-A, -B and -C) but cell adhesion was slower than control. These results suggest that high concentration of NP is toxic against tilapia hepatocytes. When effects of estradiol-17β (E₂, 10⁻⁷ M) and NP (10⁻⁴ M) on in vitro VTG synthesis were examined, addition of E₂ and NP-A and NP-B to the media resulted in elevation of VTG. NP-C did not induce VTG in the medium. Co-treatment of NP-B and tamoxifen, a non-steroidal anti-estrogen, reduced VTG synthesis. These results suggest that NP has estrogenic potential in primary cultures of tilapia hepatocytes and acts through binding to the estrogen receptor, and that there is a difference in the induction level of VTG among different NP products.     

Evaluation of carbohydrate rich diets through common carp culture in manured tanks

Four diets (T₀–T₃) were formulated reducing the fishmeal (Indian) component by 100 g kg^–1 from 300 to 0 g kg^–1 and including proportionately increasing quantities of maize. Diets were fed for 120 days at 50 g kg^–1 body weight to triplicate groups of common carp (av. wt. 2.11–2.18 g) stocked at 1 m^–2 in mud bottomed cement tanks (18 m²), fertilized with poultry manure. Fish growth, SGR and FCR in the different treatments were statistically not significantly different ( P  > 0.05). PER was lowest for the 300 g fishmeal kg^–1 diet treatment (diet T₀), increasing with decrease in dietary fishmeal content (diets T₁–T₃). Fish survival ranged from 96.29 to 100%. Diets influenced carcass composition and digestive enzyme activity. A significant increase in lipid deposition was recorded with increasing dietary carbohydrate content. Amylase, protease and lipase activities were higher in fish fed with diets T₂ and T₃. The protein sparing effect of dietary carbohydrate and the economic implication of eliminating fishmeal from the diet are discussed.     

The efficacy of emamectin benzoate as an oral treatment of sea lice, Lepeophtheirus salmonis (KrÒyer), infestations in Atlantic salmon, Salmo salar L.

The efficacy of emamectin benzoate as an oral treatment of sea lice, Lepeophtheirus salmonis (KrÒyer), infestations in Atlantic salmon, Salmo salar L., was evaluated in a dose titration study and two dose confirmation studies. Replicated groups of salmon with induced infestations of sea lice were given emamectin benzoate on pelleted feed at doses of 0, 25, 50 and 100 μg kg⁻¹ biomass day⁻¹ for seven consecutive days. Sea lice were counted at 7, 14 and 21 days from the start of treatment, and comparisons made with control fish given the same diet without emamectin benzoate. Total numbers of sea lice were significantly reduced at all doses in all three studies when compared to control fish. There was no significant difference between doses of 50 and 100 μg kg⁻¹, but the 50 μg kg⁻¹ dose resulted in significantly fewer lice than the 25 μg kg⁻¹ dose. Emamectin benzoate was highly effective in reducing numbers of preadult and adult lice and prevented the maturation of chalimus to motile stages. The optimum therapeutic dose was selected as 50 μg kg⁻¹ day⁻¹ for seven days. Treatment reduced the incidence of epidermal damage by sea lice and, in one study, survival of treated fish was 48% higher than in control groups. No fish mortalities or adverse effects were attributed to treatment with emamectin benzoate at any of the doses tested.     

A dietary energy level of 14.6 MJ kg−1 and protein-to-energy ratio of 20.2 g MJ−1 results in best growth performance and nutrient accretion in silver barb Puntius gonionotus fingerlings

Five iso-nitrogenous (300 g protein kg⁻¹ diet) and iso-lipidic (80 g kg⁻¹ diet) semi-purified experimental diets with variable energy levels of 10.5 (D-1), 12.5 (D-2), 14.6 (D-3), 16.7 (D-4) and 18.8 (D-5) MJ kg⁻¹ diets were fed to Puntius gonionotus fingerlings (average weight 1.79 ± 0.02 g) in triplicate groups (15 healthy fishes per replicate) for a period of 90 days to assess the optimum dietary energy level and protein-to-energy ratio (P/E). Fifteen flow-through cement tanks of 100 L capacity with a flow rate of 0.5 L min⁻¹ were used for rearing the fish. Maximum specific growth rate, protein efficiency ratio, protein productive value, RNA : DNA ratio, whole body protein content, digestive enzyme activity and minimum feed conversion ratio was found in fish-fed diet D-3 with 14.6 MJ kg⁻¹ energy level. There were no improvements in all these parameters with the further rise in dietary energy level. Hence, it may be concluded that the optimum dietary gross energy level for maximum growth and nutrient utilization of silver barb is 14.6 MJ kg⁻¹ diet with a resultant P/E ratio of 20.2 g protein MJ⁻¹ diet, when the dietary protein and lipid are maintained at optimum requirement levels of 300 and 80 g kg⁻¹ diet, respectively, for this species.