Outdoor Concrete Tanks Research Articles

Effect of dietary probiotics on apparent digestibility coefficients of nutrients of white shrimp Litopenaeus vannamei Boone

Apparent digestibility coefficients (ADCs) of dry matter (DM), crude protein (CP), lipid, phosphorus (P), essential amino acids (EAA), non-essential amino acids (NEAA) and fatty acids were determined for white shrimp (Litopenaeus vannamei). A probiotic (Bacillus sp.) was used at 0% (diet 1), 0.5% (diet 2), 1.0% (diet 3), 3.0% (diet 4) and 5.0% (diet 5) inclusion rates in experiment diets. Apparent digestibility coefficients was determined using 0.01% Y2O3 as an indicator. A total of 300 shrimp (initial mean body weight 11.5±0.6 g) were randomly stocked into fifteen 500-L outdoor concrete tanks. Faeces were collected from three replicate groups of shrimp three times a day. The ADCs of five diets were: DM, 66.1–69.6%; CP, 80.4–84.7%; lipid, 82.2–84.9%; P, 25.4–28.5%; EAA, 82.0–85.4%; NEAA, 81.5–85.1%; saturated fatty acids (SFA), 79.6–82.4%; monounsaturates (MUFA), 81.6–84.2% and polyunsaturates (PUFA)+highly unsaturates (HUFA), 83.4–86.6%. Apparent digestibility coefficients of DM, CP, lipid, P, amino acids and fatty acids in diet 1 were significantly lower than in other diets (P<0.05). Apparent digestibility coefficient of P in diets increased as probiotic increased. Apparent digestibility coefficient of lipid in diet 3 was the highest, but the difference was not significant among diets. In general, ADCs of most amino acids and fatty acids were over 80% in all diets, and PUFA+HUFA>MUFA>SFA. The results showed that ADCs of diets supplemented with 10, 30 and 50 g probiotic kg−1 basal diet were higher than in other diets except lipid, and the difference was significant.

Growth and body composition of rohu, Labeo rohita (Hamilton), fed compound diet: winter feeding and rearing to marketable size

Summary A 122-day growth trial was conducted to observe the impact of polyhouse in winter on growth, conversion efficiencies and body composition of fingerling Labeo rohita (7.9 ± 1.1 cm; 4.60 ± 0.18 g). Fish were stocked (1.5 m )2 ) in polyhouse and outdoor concrete tanks (250 m 2 ) in duplicate and fed a compound diet [35% crude protein (CP)] to apparent satiation twice daily, at 09.00 and 17.00 hours. A natural photoperiod was maintained during the trials. At the end of the trials, polyhouse-reared fish produced significantly (P < 0.01) higher values for weight increment, specific growth rate (SGR %), protein efficiency rate (PER), protein productive value (PPV) and better feed conversion ratio (FCR). Polyhouse-reared fish showed higher (P < 0.01) CP and fat, and lower (P < 0.01) moisture and ash contents in the muscle. In the second part of the study, which also lasted 122 days, polyhouse-reared young L. rohita (21.7 ± 1.3 cm; 127.8 ± 0.69 g) were raised to marketable size in outdoor earthen ponds (500 m 2 )a t a stocking density of 0.37 m )2 to examine the effects of feeding traditional feed mixture and compound diet (30% CP) on growth and body composition of fish. Labeo rohita fed the compound diet showed higher (P < 0.01) values for weight increment, SGR (%), PER and PPV, and better (P < 0.01) FCR than those fed traditional feed. Proximate composition of fish muscle showed higher (P < 0.05) CP and fat, and lower (P < 0.05) moisture and ash contents in fish fed the compound diet. The results suggest that polyhouse may be used successfully to culture L. rohita during winter, and that thereafter the fish may be reared in earthen ponds using the compound diet to obtain better production.

Leaching of feed nutrients, economic losses to fish farming

Seven isoproteic 40% crude protein diets were formulated and each diet was bound with different binding agents from wheat flour (WFS), Cassava tuber (CS), Maize offal (MOS), Paddy rice (RS), Yellow maize grains (YMS), Sorghum grains (SS) and Synthetic Carboxymethyl-Cellulose (CMC) as control binder. All binding agents were incorporated at 2%. Total proteins and total lipids retention at 10, 20, 30 and 60 minutes were observed in the laboratory. There were decreasing trends in the nutrients retention at increasing time of immersion in water with the lipids nutrients retention higher (P > 0.05) than the proteins. The diets were also fed to groups of Clarias gariepinus fingerlings (mean weight 2.12 ± 0.02 g) in outdoor concrete tanks. The growth and feed utilization were very related to the records produced from the nutrients retention with the WFS, CS, MOS and RS fishes recording significant differences (P < 0.05) in mean final weight; mean weight gain and feed conversion ratio over YMS and SS among the local binding agents. The economic evaluation was highest (P < 0.05) in CMC in net production value, value of fish, cost of feed, gross profit, incidence of cost and the least in profit index. However, CS binder was recommended because of its abundance in the tropics; higher nutrients retention; higher growth and feed utilization and higher economic evaluation indices among the local binders. Key words: Retention, Leaching, Diets, Catfish, Binding agents, Economic values. Journal of Aquatic Sciences Vol.18(2) 2003: 119-124

Production of Exotic &lt;I&gt;Clarias gariepinus&lt;/i&gt; Fingerlings at Varying Stocking Densities in Outdoor Concrete Ponds

The effect of stocking density on the production of exotic Clarias gariepinus fry to fingerling stage was examined during the nursery phase in outdoor concrete tanks. The fry were held at five stocking densities of 250, 500f, 750,1000 and 1250 fry/m3. There was significant difference (P < 0.05) in the mean weight gain per day and specific growth rate of fry held at the different stocking densities. The mean weight gain and specific growth rate decreased as stocking density increased. The development of “jumpers” increased as the stocking density increased. Higher stocking density gave rise to bigger “jumpers”. There was significant difference (P > 0.05) in the survival of the fry held at the different stocking densities. Highest survival was obtained at stocking density of 250 fry/m3 while stocking density of 1250 fry/m3 gave the lowest survival. Fry held at 250 fry per cubic metre gave the optimum stocking density. Key words: Exotic Clarias gariepinus, stocking density, fry, fingerling, jumper. Journal of Aquatic Sciences Vol.18(1) 2003: 21-24

Intraspecific hybridization studies in three wild strains of &lt;i&gt;Heterobranchus longifilis&lt;/i&gt; Valenciennes, 1840

Intraspecific hybridization studies were carried out in three strains of Heterobranchus longifilis obtained from three ecological zones in Nigeria – rainforest; Onitsha strain, guinea savanna; Kainji strain and montanne vegetation; Jos strain with the aim of identifying the strains and improving the growth performance of the species. The highest percentage hatchability (93.86%) was recorded in the Onitsha strain and least in the Jos strain (61.60%). Among the intraspecific hybrids, the highest percentage hatchability of 96.09% was recorded in the hybrid cross of female Kainji and male Jos while the least was in the cross involving female Jos and male Onitsha. Maximum growth recorded in five weeks of outdoor rearing was 2.460 g in the Kainji strain and minimum was 1.984 g in the Onitsha strain. Among the hybrids, maximum growth was observed in the cross involving female Onitsha and male Kainji (3.000 g) and minimum of 1.822 g recorded for female Kainji and male Onitsha. There were no significant (P > 0.05) differences in the weight of the three parental strains and the six intraspecific hybrids at hatching and six weeks of rearing indoor aquaria and outdoor concrete tanks. The best survival value of 96% was recorded for the Jos strain followed by that of the hybrid cross involving female Jos and male Kainji. Key words: strain, intraspecific hybridization, hatchability, survival, growth. Journal of Aquatic Sciences Vol.17(1) 2002: 9-12

Control of aedes vectors of dengue in three provinces of Vietnam by use of Mesocyclops (Copepoda) and community-based methods validated by entomologic, clinical, and serological surveillance.

We describe remarkable success in controlling dengue vectors, Aedes aegypti (L.) and Aedes albopictus (Skuse), in 6 communes with 11,675 households and 49,647 people in the northern provinces of Haiphong, Hung Yen, and Nam Dinh in Vietnam. The communes were selected for high-frequency use of large outdoor concrete tanks and wells. These were found to be the source of 49.6-98.4% of Ae. aegypti larvae, which were amenable to treatment with local Mesocyclops, mainly M. woutersi Van der Velde, M. aspericornis (Daday) and M. thermocyclopoides Harada. Knowledge, attitude, and practice surveys were performed to determine whether the communities viewed dengue and dengue hemorrhagic fever as a serious health threat; to determine their knowledge of the etiology, attitudes, and practices regarding control methods including Mesocyclops; and to determine their receptivity to various information methods. On the basis of the knowledge, attitude, and practice data, the community-based dengue control program comprised a system of local leaders, health volunteer teachers, and schoolchildren, supported by health professionals. Recycling of discards for economic gain was enhanced, where appropriate, and this, plus 37 clean-up campaigns, removed small containers unsuitable for Mesocyclops treatment. A previously successful eradication at Phan Boi village (Hung Yen province) was extended to 7 other villages forming Di Su commune (1,750 households) in the current study. Complete control was also achieved in Nghia Hiep (Hung Yen province) and in Xuan Phong (Nam Dinh province); control efficacy was > or = 99.7% in the other 3 communes (Lac Vien in Haiphong, Nghia Dong, and Xuan Kien in Nam Dinh). Although tanks and wells were the key container types of Ae. aegypti productivity, discarded materials were the source of 51% of the standing crop of Ae. albopictus. Aedes albopictus larvae were eliminated from the 3 Nam Dinh communes, and 86-98% control was achieved in the other 3 communes. Variable dengue attack rates made the clinical and serological comparison of control and untreated communes problematic, but these data indicate that clinical surveillance by itself is inadequate to monitor dengue transmission.

Effect of dietary protein level on the reproductive performance of Nile tilapia, Oreochromis niloticus (L.)

The effects of five dietary protein levels (25%, 30%, 35%, 40% and 45%) on the individual spawning frequency and the egg production of 135 tagged female Nile tilapia, Oreochromis niloticus (L.), were studied from 8 May to 19 November 1996 in outdoor concrete tanks. Virtually identical spawning patterns were found in all treatments, but there was a great deal of variation in the frequency of spawning and egg production. Overall, individual spawning frequency varied from one to 14 and individual egg production from 31 to 2828 eggs per spawning. The average number of spawnings and average number of eggs per spawning for fish receiving dietary protein levels of 25%, 30%, 35%, 40% and 45% were 8.0 ±1.6, 8.4 ± 2.2, 8.5 ± 2.7, 8.4 ± 2.5 and 9.4 ± 2.1 spawnings, and 1167 ± 305, 1082 ± 410, 1288 ± 324, 1145 ± 389 and 1328 ± 311 eggs per spawning, respectively. Fish receiving 45% dietary protein spawned more frequently than fish receiving 25% dietary protein. The total number of eggs produced per female was significantly higher for females fed 45% protein feed than females receiving 25% and 30% protein feeds. No definite trend was found in the number of eggs produced per spawning and the number of eggs produced per gram in females fed at different protein levels. Based on weekly checking, the time interval between spawnings varied from 7 to 77 days, and mean spawning intervals ranged from 15.8 to 17.1 days. Sixty per cent of females spawned after an interval 14 days, 15% after 21 days, 13.6% after 7 days, 7.2% after 28 days, 1.8% after 35 days and 1.0% after 42 days, and the time interval was 49-77 days for the rest of the females (1.5%). In all treatments, maximum spawning activity was recorded from May to August, and thereafter, it gradually decreased and no spawning females were found in November.

Effects of food supply on size at first maturity, fecundity and growth of hybrid tilapia, Oreochromis niloticus (L.) x Oreochromis aureus (Steindachner), in outdoor concrete tanks in Saudi Arabia

The effects of four levels of food supply (0.5%, 1%, 2% and 3% body weight daily) were investigated on some reproductive traits and growth of hybrid tilapia in outdoor concrete tanks. Fast-growing fish matured early in the season (March), but spawning started late in May. Smallest size of males and females at first maturity was 8.1 cm. Fish size at maturity appears to be influenced by the feeding level, which affects the growth of fish. For both sexes, no significant difference was found in gonadosomatic index (GSI) among different treatments. Mean percentage of mature fish decreased with decreasing food supply and was found to be significantly different between fishes fed at 3% (46%) and 0.5% (28%) body weight. Fecundity increased with increased feeding levels, although significant differences were found only between 3% and other feeding rates (0.5–2.0%). The fecundity per g female was higher at the lower ration levels (0.5% and 1%) than at the higher feeding levels. Egg quality, with respect to egg size, hatchability. fry length and weight, was not affected by the feeding rates. Final mean weight and food conversion ratios were significantly influenced by feeding rates. Higher increase in ovary weight with increasing body weight of mature females fed at 0.5% body weight than fishes receiving higher food levels suggests that in these fish, more food resources are diverted towards gonad building than to somatic growth.

Effects of food supply on size at first maturity, fecundity and growth of hybrid tilapia, Oreochromis niloticus (L.) × Oreochromis aureus (Steindachner), in outdoor concrete tanks in Saudi Arabia

Effects of food supply on size at first maturity, fecundity and growth of hybrid tilapia, Oreochromis niloticus (L.) × Oreochromis aureus (Steindachner), in outdoor concrete tanks in Saudi Arabia

Increasing attached microorganism biomass as a management strategy for Nile tilapia ( Oreochromis niloticus) production

Feeding of attached microorganisms and detrital biomass (AMDB) by Nile tilapia ( Oreochromis niloticus) was examined in two 8-week experiments conducted in outdoor concrete tanks. Although the addition of vertically placed plastic baffles and bamboo poles did not significantly increase net fish yield, differences in AMDB in tanks with and without fish clearly demonstrated AMDB was ingested by tilapia. Tilapia feeding behavior and gut analyses supported this conclusion. Because of similarities between fish and algal productivities in tanks with and without additional substrates, however, the added financial and labor costs do not warrent the use of plastic baffles or bamboo poles in static water tilapia culture systems.

Growth and reproduction of individually tagged Nile tilapia ( Oreochromis niloticus) of different strains

Growth and reproduction traits were observed in seven strains of Oreochromis niloticus from Egypt, Ghana, and Senegal (bred from wild collected stocks recently imported to the Philippines from Africa), and ‘Israel’, ‘Singapore’, ‘Taiwan’ and ‘Thailand’ (strains maintained for aquaculture purposes in the Philippines), respectively. Twenty individually tagged fish were stocked separately for each strain in 1-m 3 fine mesh hapas installed in outdoor concrete tanks and weighed every 2 weeks from 60 days to 210 days. There were no significant differences ( P<0.05) in growth among strains with the exception of Ghana which showed a significantly lower body weight at 210 days ( P<0.05). Based on ages at first spawning, three phenotypes of females were distinguished: early spawning, late spawning and females that did not reproduce during the experiment (virgin females). Growth performances of late spawning and virgin females were nearly equal to the male growth performance in some of the strains tested. This indicates that if reproduction can be delayed in the females, average growth rates comparable to those of an all-male population might be achieved. Phenotypic correlations observed between age and female body weight at first spawning ranged from O.77 to 0.99; age and number of eggs at first spawning, 0.30 to 0.81; and female body weight at first spawning with the number of eggs produced, 0.64 to 0.76. Overall, the correlations between these traits were significant ( P<0.05).

ティラピアＴｉｌａｐｉａ ｍｏｓｓａｍｂｉｃａの釣られ易さの個体差

To determine the individual catchability of fish, angling experiments were conducted using five groups of tilapia in an outdoor concrete tank 10×5×0.65m in dimensions. The effects of previous experience of hooks, the hunger level, and the presence of eggs on catchability were determined using chi-square analysis. Five different baits were used at random to eliminate the effect of bait preference. At the start of experiments, about half of each group were hooked, marked by fin clips, and released back in to the tank with the unmarked fish. A recapture trial was repeated twice by angling and tallying marked and unmarked fish. Fish were thus hooked a total of three successive times, twice, only once, or_not at all. After the angling experiments, fish were given pellets and allowed to feed for 10-20 minutes, then examined for the amount of intake and the presence of eggs. Results indicated that fish that had been hooked earlier tended significantly to be hooked again. Fish did not learn to avoid hooks. Fish that had been hooked tended to eat more. Fish with eggs tended to be less catchable, but individual differences in catchability were also found among those without eggs.

Effects of water exchange on Oreochromis niloticus (L.) growth and water quality in outdoor concrete tanks

Fingerlings of Oreochromis niloticus (L.) (av. wt. 19.0 g) were stocked in 3.75-m 3 outdoor concrete tanks at 240/tank, and reared for 98 days to evaluate the effects of rate of water exchange on growth, feed conversion and water quality. The average harvest weight of fish ranged from 122.4 to 87.6 g. The best growth was obtained with a continuous flow rate of 11/min per kg biomass (specific growth rate (SGR) 1.80, average daily gain (ADG) 1.06 g/day), closely followed by fishes receiving 0.5 l/min per kg (SGR 1.74, ADG 0.94 g/day). The poorest growth (SGR 1.46, ADG 0.7 g/day) occurred when the water was batch changed once every 24 h. With two batch changes daily, the average SGR and ADG were 1.63 and 0.86 g/day respectively. The feed conversion ratios ranged from 1.7 to 2.3, being low in tanks with continuous flow and high in tanks with batch exchange. As there was no significant difference in growth performance in two sets of flow-through tanks, a flow rate of 0.5 l/min per kg appears to be desirable for intensive culture of tilapia.

Effects of feeding supplementary diets containing varying levels of lipid on growth, food conversion, and body composition of Nile tilapia, Oreochromis niloticus (L.)

Young, male tilapia, Oreochromis niloticus (L.) were stocked in 3500-litre outdoor concrete tanks at densities of 1.7 fish/m 2 and fed diets containing 5, 9 and 12% lipids, or 34, 29 and 26 mg crude protein/kJ DE at a rate of 3% of their wet biomass per day. The diets were labelled the low-lipid (LL), medium-lipid (ML), and high-lipid (HL) diet. Increasing the dietary lipid level produced no significant effects on growth rate (SGR from 1.55 to 1.58%/day), food conversion ratio (FCR from 0.60 to 0.65 g gain/g feed), and protein gain (e.g. Trial 1: % PD from 20.8 to 23.0%). In contrast, percent energy retained varied between the trials ( P<0.05), and between fish fed the different diets (e.g. Trial 1:35.8–40.4%), being highest in fish fed the LL and ML diets in Trial 1, and in fish fed the ML diet in Trial 2 ( P<0.05). It was recognized that the effects of the diets may have been masked by an unquantified input of food energy from the natural production of micro-algae within the water of the tanks. Changes in body composition were not significant with respect to moisture and protein content of the carcass (moisture 73–75%; protein 13.8–15.2% in Trial 1 and 16.2–16.6% in Trial 2 with a significant difference between the trials [ P<0.05]). Increasing the dietary lipid level effected a significant increase in the level of carcass and visceral lipid (carcass lipid from 1.2% in control fish to 4.5–7.9% in fish fed the supplementary diets; visceral lipid from 1.3% to 10.7–18.5% in control and supplementary-fed fish, respectively). It was concluded that the tilapia were able to store significant quantities of lipids in the carcass and the viscera, but were not able to utilize this energy source to improve growth or food utilization efficiency, at least in diets containing adequate levels of protein, or under conditions where it was possible for natural productivity in the water to add unknown, but possibly considerable quantities of dietary protein and energy. Diets for tilapia culture may therefore have to be compounded on the basis of protein rather than energy considerations.

Culture of Nile tilapia, Oreochromis niloticus (L.), at three stocking densities in outdoor concrete tanks using drainage water

. Effects of stocking density on water quality and on the growth, survival and food conversion of Oreochromis niloticus (Linnaeus) were evaluated. Fingerlings of tilapia (average weight 40.25 ± 94 g) were stocked in six 3.75-m3 concrete tanks at 16, 32 and 42.6/m3 and reared for 164 days. A water flow rate of 1 l/min/kg fish biomass was maintained in all the tanks. The growth rate was inversely related to stocking density with mean weights of 337.25g, 327.0g and 323.5g at the low, medium and high densities respectively. At harvest, standing crop biomass averaged 5.36 kg, 10.44kg and 13.24kg for the three densities. The respective food conversion ratios (FCR) were 1.85, 1.88 and 1.95, while the survival rates were 99.2, 99.6 and 95.9%. However, the survival rate, growth rate and food conversion efficiencies were not significantly different at the three stocking densities. Water quality did not deteriorate in different tanks as the oxygen was continuously replenished and metabolites and waste products removed by the water flowing through the tanks. These data suggest that culture of tilapia at a density of 42.6/m3 and production of 13.24 kg/m3 in 164 days with a production of 18–20 kg/m3 in a growing season (April-October) of 210 days is possible using the drainage water in flow-through water systems.

The growth and survival of hatchery-reared Ostrea edulis L. spat in relation to environmental conditions at the on-growing site

Growth and survival of hatchery-reared Ostrea edulis L. spat were compared at three sites in North Wales during 1983. Two sites, at Tal-y-foel and the Inland Sea, were natural. The third site, at Conwy, was a more controlled environment in outdoor concrete tanks containing fertiliser-enriched sea water. Newly planted spat, 1.2–5.7 mg live weight, usually grew better at Inland Sea than at Conwy. Spat exceeding 300 mg live weight in the natural area grew less well than expected for the pre-vailing sea water temperatures because of an inadequate food supply. At Conwy, however, spat with a larger weight than 300 mg continued to grow well because phytoplankton was plentiful. Growth at Tal-y-foel was usually less than expected for the prevailing temperature. The possibility that growth was suppressed by high levels of particulate inorganic material (PIM) in the water is discussed. Greatest mortalities of spat normally occurred during the month after planting.

DEVELOPMENTAL STAGES IN THE FLORAL BIOLOGY S.L. OF DUTCH NYMPHAEACEAE (NYMPHAEA ALBA L., NYMPHAEA CANDIDA PRESL, NUPHAR LUTEA (L.) SM.)

Acta Botanica NeerlandicaVolume 35, Issue 2 p. 111-113 Brief Communication DEVELOPMENTAL STAGES IN THE FLORAL BIOLOGY S.L. OF DUTCH NYMPHAEACEAE (NYMPHAEA ALBA L., NYMPHAEA CANDIDA PRESL, NUPHAR LUTEA (L.) SM.) G. van der Velde, G. van der Velde Laboratorium voor Aquatische Oecologie, Katholieke Universiteit, Toernooiveld, 6525 ED NijmegenSearch for more papers by this author G. van der Velde, G. van der Velde Laboratorium voor Aquatische Oecologie, Katholieke Universiteit, Toernooiveld, 6525 ED NijmegenSearch for more papers by this author First published: May 1986 https://doi.org/10.1111/j.1438-8677.1986.tb00467.xCitations: 10AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat Citing Literature Volume35, Issue2May 1986Pages 111-113 RelatedInformation

Ecology and Rearing of a Leaflike Shrimp Nebalia sp.

A leaflike shrimp Nebalia sp., which belongs to the most primitive genus of Malacostraca, has been found abundantly at the base of Bryopsis sp. growing in an outdoor concrete tank used for Homarus culture at Sanriku. The species is considered to be desirable as a living food organism for larval rearing because of its suitable size and tolerance to deterioration of the bottom condition.Sampling was done in the pond from July to December of 1983. Water temperature ranged from 22.3°C in summer to 4.5°C in winter. The animals were found throughout the season with the highest occurrence of egg-bearing females in October. The larvae were reared successfully at water temperature between 15°C to 25°C in combination with the salinity between 20‰ to 33‰ under the continuous darkness. The larvae showed the best growth at 25°C in combination with 33‰. The most effective food for the larval rearing in the laboratory was the fine particles of the dried food as shrimp pellet and krill.The larvae hatched out as adult form. Number of segments in the flagellum branches of the first antenna and the second antenna increased from 3:3, expressed as segmentation formula, at I stage to 4:3, 5:4, 6:5, 7:6 and 8:7 at II, III, IV, V and VI stages, respectively. After VII stage, the increase became irregular.

Androgen-induced sex-inversion of Oreochromis (Trewavas) hybrid fry stocked into cages standing in an earthen pond

Gonadally undifferentiated Oreochromis niloticus × O. aureus hybrid fry (F 2 generation), were fed a single level of androgen-treated diet (60 mg/kg 17-α-ethynyltestosterone), in earthen pond cages, an indoor tank and outdoor concrete tanks. All fry fed androgen-treated diets had populations consisting of ≥ 96% males, whilst those populations fed control diets had sex ratios which were not significantly different from an expected 1:1. No all-male broods were obtained, but populations composed of 96% and 99% males were produced in earthen pond cages following 25- and 28-day treatment periods, respectively, at a mean temperature of 30°C. Fry in outdoor pond cage treatments appeared to grow faster than those inside. Additional, naturally occurring food in the ponds is considered partly responsible for this. Survival of fry during androgen treatments depended upon size and density at stocking. Larger and more vital fry survived better than newly hatched fry.

Effects of estrogens on Tilapia aurea: Implications for production of monosex genetic male tilapia

Three naturally occurring estrogens, estriol, estrone and 17-Beta estradiol, were each administered perorally at three concentrations for 3- or 5-week periods to fry of Tilapia aurea, 8–11 mm long. Estrogen treatment neither affected survival nor altered growth of fry. Post-treatment stocking in outdoor concrete tanks revealed no apparent differences in survival between hormone-treated and untreated fish after 99–148 days. Gonadal examination of treated and untreated groups after growth trials revealed no aberrant sex ratios in the groups treated with estrogen, but in all treatment groups there were significant proportions of males with a female-like urogenital papilla. Greater proportions of such ‘atypical’ males occurred at the higher estrogen dosage levels and in the longer treatment period. No atypical males were found in the control groups. Sexing of fish that died after treatment indicated no difference in the death rate of the sexes. Histological examination of gonads revealed no alteration of normal male and female germ cell development; pseudo-oocytes were present in both treated and untreated groups. No ovotestis condition was observed. Male and female homogamety among different tilapia species and a method for producing monosex genetic males from matings of sex-reversed brood stock are discussed.