Effect of synthetic GnRH analogues and dopamine antagonists on the maturation of Pacific mullet, Mugil so-iuy Bas.

Abstract. The effect of two GnRH-As – des Gly¹⁰ (D-Ala)⁶ LHRH and des Gly¹⁰ (D-Tle)⁶ GnRH in total doses 10–249mu;g/kg – and four neuroleptics – pimozide, sulpiride, metoclopramide and isofloxythepin in total doses 1–50mg/kg - and environmental temperatures on the development of final stages of Pacific mullet oogenesis was investigated. The best technique of those used by us for spawning stimulation of Pacific mullet, Mugil so-iuy Bas., females is shown to be administration of neuroleptics in doses of l-8mg/kg with posterior injections on GnRH-A in doses of 25 and 50mu; g/kg applied 4 and 28h respectively after the neuroleptic injection. At water temperatures below 17°C, ovulation does not occur unless the optimal stimulation is applied.     

Ovulation and egg survival following exposure of Atlantic salmon, Salmo salar L., broodstock to different water temperatures

Abstract The timing of ovulation and survival of eggs following exposure of 2-sea-winter Atlantic salmon, Salmo salar L., to different temperature regimes during the spawning season were investigated. Water temperature was either increased from 10 to 13–14°C (warm water), decreased abruptly from 10 to 5–7°C (cold water), or gradually decreased from 10 to 8°C (ambient control) from 1 November onwards. Median ovulation time was delayed by 5 weeks in the warmwater group compared with ambient controls, with 43% of the females remaining non-ovulated at the end of the study. Only minor effects were observed on timing of ovulation in the coldwater group compared with ambient controls. Survival of eggs to the eyed stage was significantly higher in the coldwater group (92·1%), compared with both the ambient control group (84·5%) and the warmwater group (76·6%). The results indicate that high water temperature during the spawning season inhibits ovulation and has a detrimental effect on gamete quality in Atlantic salmon.     

Reproductive biology of whitespotted bamboo shark Chiloscyllium plagiosum in northern waters off Taiwan

ABSTRACT:   In total, 491 whitespotted bamboo sharks were collected from northern Taiwanese waters from February 2002 to February 2003. The sex ratio of the specimens was 0.65, total length (TL) ranged from 35.3–85 cm, and weight ranged 124–2580 g. The mean size at first maturity was estimated to be 64.9 and 65.6 cm TL for females and males, respectively, based on the relationship between mature percentage and TL. The ovulation season was estimated as March to May based on gonadosomatic index (GSI) variations and captive observation. The monthly changes in GSI of males suggested that the mating season was from December to January. The inconsistency between mating and ovulation seasons suggested that females have sperm storage and delayed fertilization. One or two eggs were deposited every 6 or 7 days on average. Deposition of eggs extended for 2 months, and fecundity was 8 ± 3.8 eggs. Thirteen of 48 eggs deposited in 2003 were hatched and the hatching rate was 0.27. The hatching period was 107 ± 9.3 days with accumulated water temperature ranging from 2372–2835°C.     

Effect of different synthetic gonadotrop-releasing hormone analogues and their combinations with an anti-dopaminergic compound on the reproduction performance of sterlet (Acipenser ruthenus L.)

In this study, three synthetic gonadotrop-releasing hormones (GnRH) (azagly-nafarelin; des-Gly¹⁰-( d -Ala⁶)-LH-RH; and des-Gly¹⁰-( d -Phe⁶)-LH-RH) either alone or in combination with metoclopramide were used to induce reproduction of sterlet. The GnRH analogues were applied in a single dose of 40 μg kg⁻¹ of female and 20 μg kg⁻¹ of male body weight. Metoclopramid was administered in a simultaneous injection of 10 and 5 mg kg⁻¹ of body weight for females and males respectively. There were no significant differences in the ovulatory responses of females; ovulation rates varied between 57% and 80%, and at the temperature of 15.5–16.0 °C about 30–34 h were required for final maturation, when eggs of 17.3±1.3% of body weight were stripped. However, the fertilization rates of the des-Gly¹⁰-( d -Phe⁶)-LH-RH-treated groups were significantly lower than that in the other treatment. In males, the combination of the above peptidergic hormones with metoclopramide gave significantly better results than their single application. The results demonstrate that the final stage of gamete maturation in sterlet may be achieved by several hormonal means. The possibility of using new GnRH analogues without dopamine antagonists yields new perspectives for induced breeding of sturgeons, which have particular importance in the light of meat and roe (caviar) production for human consumption.     

Induced Ovulation of Southern Flounder Paralichthys lethostigma Using Gonadotropin Releasing Hormone Analogue Implants

Implanted pellets that provide a sustained release of [D-Ala⁶ Des-Gly¹⁰] LHRH-ethylamide (GnRHa) were used to induce maturation and ovulation of Southern flounder Paralichthys lethostigma . Of the 12 females whose ovaries contained follicles with a maximum diameter ≥500 μm, 11 ovulated for the first time within 90 h of hormone implantation. Only 1 fish with a maximum follicle diameter less than 500 μm ovulated within 2 wk after implantation. Ovulated eggs were manually stripped from the females and mixed with sperm from several males. Most females were spawned 1 to 3 times on consecutive days with variable fertility. One female was spawned 11 times producing 668,000 eggs. Fertility was evaluated by examining the incubated eggs for early stages of embryonic cleavage. The percentage of fertile eggs in subsamples of incubated eggs ranged from 7–95%. The results indicate that GnRHa implants can be used to induce repeated ovulation in this species. The variability in fertility is discussed in relation to egg quality.     

Characterization of depth-related changes and site-specific differences of microbial communities in marine sediments using quinone profiles

ABSTRACT:   Respiratory quinone compositions were analyzed by a high-performance liquid chromatography to characterize the depth-related changes and site-specific differences of microbial communities in marine sediments. Two deep-sea sediment samples and one coastal sediment sample were investigated from three sites on the coast of Japan, Sagami Bay, Suruga Bay and Tokyo Bay. Although depth-related changes in microbial community structures were observed, site-specific differences appeared to have greater influence on overall community structures. A variety of quinone homologs was commonly identified at all sampling sites and depths examined, but a few minor quinone fractions, mainly derived from Actinobacteria , were detected only at specific sampling sites. Methylmenaquinone-7 (MMK-7) was the major component throughout the examined depths in Sagami Bay and Tokyo Bay. Most abundant quinone homologs changed with each depth in Suruga Bay. Menaquinone-6 (MK-6) predominated in the 0 to 2-cm layer (19%). Below 0–2 cm, the most abundant homolog in each sampling depth was phylloquinone (K₁; 13%, 4–6 cm), MK-8 (19%, 8–10 cm) and MK-7 (13%, 16–18 cm). The microbial respiratory quinone profiling method shown here, successfully demonstrates the usefulness of this approach to characterize microbial communities in marine sediments.     

Efficacy of human chorionic gonadotropin (hCG) and crude pituitary extract of fish and frog in oocyte maturation and ovulation in African catfish, Clarias gariepinus Burchell, 1822 and Clarias anguillaris L., 1762

Abstract. The African catfish, Clarias gariepinus Burchell and Clarias anguillaris L., were induced to ovulate in aquaria by the administration of human chorionic gonadotropin (hCG) and pituitary extracts of Clarias albopunctatus (Nichols & Lamonte) and frog, Rana elegans. For final maturation and ovulation in both species of Clarias , the total dosage of each hormone was inversely proportional to the initial oocyte diameters of the recipient females. The time of ovulation after the last injection (latent period) was significantly shorter (11–13h) in females with large oocyte diameters (>920μm) than in those whose mean oocyte diameters were less than 920 μm (13–16h) ( P < 0·05). The mean dosage of each test hormone required to induce ovulation was lower in females with large oocyte diameters than in those with smaller oocyte diameters (<920μm). The mean percentage hatch did not depend significantly on the nature of the treatment ( P > 0μ05) and was about 86%. Clarias albopunclatus and R. elegans , which are economically unimportant and abundant in Anambra River basin, Nigeria, could be used as effective sources of hypophyseal factors in Clarias breeding programmes.     

多巴胺拮抗物 pimozide(PIM)或排除剂 reserpine(RES)和促黄体素释放激素类似物(LHRH-A)诱导养殖鱼类促性腺激素分泌和排卵的研究

由多巴胺拮抗物PIM或排除剂RES组成的高效新型鱼类催产合剂能有效的诱导主要的淡水养殖鱼类促性腺激素分泌和产卵，其中青鱼催产率为80％，鲢鱼为84％，鳙鱼和草鱼为88％，长春鳊为94％，鲮鱼为96％。试验表明这种催产剂的主要优点是：催产效果高而稳定，可以完全取代鱼脑垂体；对当年第二次成熟和产卵的亲鱼同样有效；有利于保护亲鱼；节省劳力和成本。     

Strategies for Development of Rotifers as Larval Fish Food in Ponds

Strategies to sustain rotifer peak biomass, distribution of rotifer resting eggs in the sediment, and relationship between rotifers and larval fish growth were studied in a series of pond experiments. After the ponds were filled with water, herbivorous rotifers (e.g., Brachionus calyciflorus ) developed first, but were gradually replaced by predatory rotifers (e.g., Asplanchna ). Subsequently, herbivorous cladocerans (e.g., Moina sp) eventually replaced rotifers and dominated the zooplankton community. The occurrence of Asplanchna and Moina indicated the decline of B. calyciflorus . Peak rotifer biomass developed 8–10 d after the ponds were filled with water at 20–25 C, 10–15 d at 17–20 C, 15–20 d at 15–17 C, 20–30 d at 10–15 C, and >30 d at < 10 C. The abundance of resting eggs in the top 5-cm sediment varied from 6 to 83/cm². About 25% of resting eggs were buried in the top 5-cm sediment but the number of resting eggs decreased with increased sediment depth. Optimum rotifer biomass for silver carp Hypophthalmichthys molitrix larvae stocked at 1,500,000/ha was 20–40 m/gL. High rotifer biomass (>20 mg/L) usually lasted 3–5 d, but could be prolonged by pond fertilization or cladoceran controls. A weekly application of dipterex at 0.05 mg/L reduced cladoceran biomass but enhanced rotifer biomass. Our results indicate with a careful management plan it is possible to synchronize the rotifer development with larval fish stocking.     

Effects of photoperiod on sex steroids and gonad maturation in Arctic charr

Four groups of Arctic charr (age 3+), previously exposed to natural photoperiod, were subjected to different photoperiod regimes from February 20: Simulated natural photoperiod (SNP; Tromsø 70°N), continuous light (LD 24:0) followed by short day (LD 6:18) from either May 1 (L_Feb–May) or June 25 (L_Feb–June), or continuous light (LD 24:0) throughout the experiment (L_Continuous). In females, peak levels of estradiol-17β and testosterone were 6 and 10, 6 and 7, and 3 and 5 weeks advanced, in L_Feb–May, L_Feb–June and L_Continuous, respectively, whereas in males plasma levels of 11-ketotestosterone peaked 8 weeks earlier in L_Feb–May and L_Feb–June than in SNP and L_Continuous. Median ovulation time in L_Feb–May and L_Feb–June was advanced by 10 weeks compared to SNP and L_Continuous, and median spermiation time (first observation of running milt in each individual) in L_Feb–May, L_Feb–June and L_Continuous was advanced by 10, 7 and 5 weeks, compared to SNP. A switch from long to short day early in the reproductive cycle (L_Feb–May and L_Feb–June) apparently resulted in stronger synchronization of both ovulation and spermiation. Ovulation in L_Feb–May and L_Feb–June occurred over 3 weeks (L_Feb–May) and 8 weeks (L_Feb–June), as compared to 10 weeks in the SNP group, whereas all males (except one individual) began spermiating over a period of 3 weeks (L_Feb–June), or less (L_Feb–May), as compared to 7 weeks in the SNP group. Lack of a short day stimulus (L_Continuous), on the other hand, resulted in larger variation in the timing of final maturation, with ovulation and spermiation being spread over 15 weeks. Low egg survival in L_Feb–May (17% versus 60% and 97% for L_Continuous and SNP) indicate that a long day signal of 10 weeks early in the reproductive cycle may be too short to ensure good egg and sperm quality. Photoperiod manipulation did not affect the proportion of maturing fish.     

Effect of Oxygen Saturation in Water on Reproductive Performances of Pacu Piaractus brachypomus

Broodstock pacu Piaractus brachypomus as well as their eggs during their embryonic development were exposed to either normoxia (5.5–7.5 mg O₂/L) or hypoxia (2.0–4.5 mg O²/L) conditions. The plasma concentrations of 11-ketotestosterone in males and estradiol-17β in females, as well as that of their precursor testosterone (T) were significantly ( P < 0.01) higher in fish maintained under normoxic conditions than in fish exposed to hypoxia. After ovulation and spermiation induced by hormonal treatments, the plasma concentrations of T and 17,20β-dihydroxy-4-pregnen-3-one (17,20βP) significantly ( P 0.05) increased in both sexes under both normoxic and hypoxic conditions. The plasma levels of T and 17,20βP achieved under normoxic conditions were higher than the ones recorded under hypoxia, except for those of 17,20βP in males. Males responded positively to the hormonal treatments, and the concentration of spermatozoa was 10.5 ± 0.8 10⁹/mL under both oxygen conditions. Hypoxia resulted in significantly lower survival of embryos (17.3 ± 28%) in comparison to normoxic conditions (68.5 ± 25%). Moreover, larval deformities were found when exposed to hypoxia (91.6 ± 6%). During embryonic development of this species 4 mg/L of oxygen is tolerated at 26–27 C without negative impact. We conclude that despite the highly adaptable nature of adult pacu to environmental hypoxia, oxygen concentrations below 4 mg/L severely impacted survival of embryos.     

Induced ovulation of yellow catfish (Pelteobagrus fulvidraco) using a combination of a gonadotrop‐releasing hormone analogue and domperidone

The effects of an intraperitoneal hormone injection of gonadotropin‐releasing hormone agonist (D‐Ala⁶, Pro⁹‐NEt GnRHa) alone or in combination with a dopamine antagonist, domperidone (DOM), on ovulation induction in yellow catfish Pelteobagrus fulvidraco were tested. The hormone treatments were as follows: 6 mg kg⁻¹ body weight (BW) of carp pituitary extract as a positive control, GnRHa 10, 20, 40 and 80 μg kg⁻¹ BW and a combination of GnRHa and DOM as follows: 10 μg+5 mg, 20 μg+10 mg, 40 μg+20 mg and 80 μg+40 mg kg⁻¹ BW. Physiological saline (0.7% NaCl) was used as a negative control. Significant differences in the ovulation ratio, latency period and ovulation index (OI) were observed among treatments (P<0.05). The combination of GnRHa and DOM at doses of 40 μg+20 mg kg⁻¹ BW had higher values of the ovulation ratio and OI, and a shorter latency period compared with other treatments. The highest OI in GnRHa treatments was only 56.67%, suggesting a dopaminergic tone on gonadotropin secretion in this fish at the pre‐ovulatory stage. Therefore, ovulation can be successfully induced in yellow catfish with 40 μg kg⁻¹ GnRHa+20 mg kg⁻¹ DOM without affecting the egg quality.     

Effect of dietary protein, lipid and carbohydrate content on the growth, feed efficiency and carcass composition of striped bass, Morone saxatilis (Walbaum), fingerlings

Abstract. Two 6-week experiments were conducted with age-0 striped bass, Morone saxatilis (Walbaum). In the first experiment, fish were fed isocaloric diets that contained 20–65% protein. In the second experiment, fish were fed isonitrogenous diets (42–46% protein) that contained 6–29% dextrin or 8–25% cod liver oil.
Maximum weight gain, feed efficiency and protein efficiency ratio were achieved with a 52% protein diet. Net protein utilization was inversely related to dietary protein concentration.
In the second experiment, maximum growth was achieved with a 33% carbohydrate diet (based on nitrogen free extract); and with a 17% lipid diet (based on ether extract). Increasing dietary lipid beyond 17% resulted in growth depression. No negative impacts on carcass composition as a result of increasing dietary dextrin or lipid were judged to have occurred.     

Influence of the Dietary Level of Iron from Iron Methionine and Iron Sulfate on Immune Response and Resistance of Channel Catfish to Edwardsiella ictaluri

Channel catfish Ictalurus punctatus fingerlings were fed purified diets supplemented with iron at levels of 0, 20, 60, and 180 mg/kg from iron sulfate (FeS) or 5, 10, 20, 60, and 180 mg/kg from iron methionine (FeM) in triplicate tanks for 8 wk. Fish were then divided into two groups and subjected to different assays to measure disease resistance and individual immune functions. Representative fish from each dietary treatment were challenged by bacterial immersion with virulent Edwardsiella ictaluri , and mortality due to enteric septicemia was recorded. Other fish were immunized with 0.2–mL formalin-killed E. ictaluri and boosted 21 d post-immunization. Antibody response was determined by FAST-ELISA. Chemiluminescent and chemotaxis assays were performed using peritoneal macrophages. Supplementation of the diet with various levels of iron from FeS or FeM did not significantly affect antibody production. Chemotactic migration by macrophages was depressed in iron-deficient fish and a level of 60 mgkg from either FeS or FeM provided the highest chemotactic indexes. A deficiency of dietary iron was found to increase mortality of channel caffish due to enteric septicemia of catfish (ESC). However, more studies should be conducted to better understand the effects of sources and levels of dietary iron on immune responses and disease resistance in channel caffish.     

线粒体COI基因条形码在鲿科鱼类物种鉴定中的应用

为了探讨线粒体COI基因作为DNA条形码在中国鲿科(Bagridae)鱼类物种鉴定中的有效性,以及系统发育中的适用性,本研究对4属11种鲿科鱼类进行PCR扩增,获得48条线粒体COI基因序列,同时从Gen Bank筛选获得8种鲿科鱼类的12条COI基因序列进行分析。19种鲿科鱼类的COI基因序列特征显示:长度为674 bp的COI序列片段平均碱基组成为24.82%A,30.44%T,27.10%C和17.64%G,碱基组成呈现明显的AT偏倚性(55.26%),具有硬骨鱼类的线粒体COI基因的碱基组成的典型特征。核苷酸位点中有变异位点226个,简约信息位点195个,单一信息位点31个,转换颠换比为3.35。19种鲿科鱼类的种内、种间和属间平均遗传距离分别为0.0041、0.1136和0.1268,种间遗传距离平均为种内遗传距离的27.7倍。在本研究中,鲿科鱼类所有的物种均形成单系,在物种鉴别上与形态学分类结果基本一致,然而鲿科的4个属中只有鱯属形成单系,黄颡鱼属、属和拟鲿属均未形成单系,其进化地位需要进一步研究。线粒体COI基因作为条形码可有效对鲿科鱼类进行物种鉴定,也为鲿科的系统发育提供了参考。     

Mass Production of Striped Patao Eugerres brasilianus Juveniles in Cuba

Abstract.— Two spawning and larval rearing trials with striped patao Eugerres brasilianus were conducted at Tunas de Zaza, Cuba, to develop a method for experimental-scale mass production of juvenile fish. Mature striped patao were captured from coastal lagoons in September 1988 and January 1989. Sexually mature females and males were induced to spawn by treatment with human chorionic gonadotropin (HCG). After spawning, eggs were collected and placed in 1.2-m³ cylindroconical fiberglass incubators at densities of 150 and 200 eggs/L. About 1 h before hatching, eggs were transferred to 5–m³ concrete tanks. Larvae were fed a mixture of marine microalgae, rotifers, copepods, and Artemia nauplii; artificial food was supplied at 30 d post-hatch as a shrimp diet with 25% protein and 0.1–0.4 mm particles. Fourteen of 20 females spawned after 2 or 3 HCG injections (total dose = 6–10 IU/g body weight). Fecundity was 467–2,167 eggs/g body weight. Egg incubation time in seawater (38–39 ppt salinity) was 15–17 h at 29–30 C and 21–23 h at 25–26 C, with 98–100% hatching rate. The oil droplet and yolk sac were consumed by 3 to 5 d post-hatch and first food (rotifers) was eaten during second day. High larval mortalities began after the first month. Growth in 39- ppt seawater was faster (0.41 ± 0.01 md/d) at 29.1 ± 0.3 C than at 25.2 ± 0.2 C (0.27 ± 0.008 mm/d). Overall survival was 6–12.5% with tinal densities of 5–10 juveniles/L after 48–60 d. A total of 132,000 juveniles was harvested from the two rearing cycles.     

Controlled reproduction of an important indigenous fish species, Spinibarbus denticulatus (Oshima, 1926), in Southeast Asia

Aquaculture of Spinibarbus denticulatus (Oshima, 1926), a fish species indigenous to North Vietnam and Eastern China, is constrained by lack of fingerlings for stocking ponds and cages. As these fish do not naturally breed in captivity, carp pituitary extract (CPE), luteinizing hormone-releasing hormone analogue (LHRHa) with domperidone (DOM) and human chorionic gonadotropin (HCG) were administered at various doses to induce ovulation. A first set of experiments evaluated the response to LHRHa (30, 40 and 50 μg kg⁻¹) with or without DOM (10 mg kg⁻¹), CPE (20, 30 and 40 mg kg⁻¹) and HCG (3000, 4000 and 5000 IU kg⁻¹). A second set of experiments evaluated the dose response to LHRHa (30, 35, 40 and 50 μg kg⁻¹) primed with 6 mg kg⁻¹ of CPE, and HCG (3000, 3500, 4000, 5000 IU kg⁻¹) primed with 6 mg kg⁻¹ of CPE. The treatment groups were compared with each other and the control (injected with 0.9% saline solution). Only 25% and 50% ovulation resulted when treated with LHRHa at 40 and 50 μg kg⁻¹, whereas 100% ovulation was achieved with an addition of DOM to LHRHa. Both 30 and 40 mg kg⁻¹ CPE induced 100% ovulation. However, HCG (4000 and 5000 IU kg⁻¹) induced ovulation in only 33% of females. When primed with CPE, the minimum dose of LHRHa required was 35 μg kg⁻¹ to achieve 70% ovulation. Priming HCG with CPE also resulted in 100% ovulation, and the minimum effective dose of HCG to induce ovulation was 3500 IU kg⁻¹ with 60% ovulation. Fertilization and hatch rates observed in this study with different hormonal stimulation were high (80–93%). The results indicate that while the use of combined hormone strategy has no apparent advantage over a single hormone strategy, LHRHa+DOM (40 μg kg⁻¹+10.0 mg kg⁻¹) and CPE (30 mg kg⁻¹) are most effective in consistently inducing ovulation and thus can be used for commercial hatchery production of S. denticulatus larvae.     

Artificial spawning of female Lithuanian strain B carp (Cyprinus carpio L.) after treatment with carp pituitary homogenate, Ovopel or [d-Tle6, ProNHEt9] GnRH-a (Lecirelin)

The results of reproduction of females from Lithuanian strain B carp after ovulation stimulation with carp pituitary homogenate (CPH; 0.3+2.7 mg kg^?1; group I), Ovopel (1/5+1 pellet kg^?1; group II) or [d ‐Tle⁶, ProNHEt⁹] GnRH‐a (Lecirelin) with metoclopramide (15 μg kg^?1+10 mg kg^?1 respectively; group III) were investigated. The lowest percentage of spawning females (71%) was recorded in the group treated with CPH. In case of Ovopel or Lecirelin induced ovulation, 86% of females spawned. No statistically significant effect of the ovulation stimulator (group) on the weight of eggs was found; however, the highest mean weight of eggs (expressed both in grams and in the percentage of female body weight) was recorded for the group treated with Ovopel (1400 g and 13%). After the treatment with CPH or Lecirelin, the weight of eggs was 1140 g (11%) and 1100 g (10%) respectively. The ovulation stimulator significantly affected the percentage of live embryos after 36 and 48 h incubation of eggs (P≤0.05; P≤0.01). After treatment with [d ‐Tle⁶, ProNHEt⁹] GnRH‐a, eggs of the best quality were obtained and after 36 and 48 h incubation the mean percentages of live embryos were significantly higher than the means calculated for the remaining two groups. No statistically significant differences were found between the percentage of living embryos after 36 and 48 h incubation of groups I and II.     

Different combinations of protein ingredients in carp diets for reducing phosphorus loading

ABSTRACT: This study was conducted to gather data on the reduction of environmental phosphorus (P) loading through the formulation of carp diets with different combinations of protein ingredients. Five experimental diets were formulated by substituting fishmeal (FM; 10–20%) with alternative protein sources such as meat meal (MM; 5–15%), blood meal (BM; 5–7%), and defatted soybean meal (dSBM; 6–10%). The control diet used was a commercial carp diet selected based on earlier experiments. Each diet was fed to duplicate groups of juvenile carp three times a day, until satiation for 12 weeks. Feed performance was proportional to the increase in dietary FM levels. Phosphorus absorption ranged between 41.6% and 52.0% among the experimental groups and was 42.6% for the control group, but there were no marked differences in nitrogen (N) absorption rates. Phosphorus retention ranged from 31.4% to 35.7% for the test diets, whereas N retention increased proportionally with dietary FM levels and ranged from 34.7% to 41.7%. The P and N retention values of the control diet were 27.6% and 41.2%, respectively. The total P loading (T-P) increased at the higher FM levels (9.1–10.7 kg/t production), whereas lower FM levels produced higher total N loading (T-N, 34.6–43.1 kg/t production), the figures for the control being 13.9 T-P kg/t production and 35.6 T-N kg/t production. These results indicate that the reduction of FM levels to 10–20% by replacing it with MM, BM, and dSBM in carp diets was effective in reducing the loading of P and N.     

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.