Monosex Nile Tilapia Research Articles

Effects of Dietary Protein Level on Growth Performance, Carcass Composition and Survival Rate of Fry Monosex Nile Tilapia, Oreochromis niloticus Reared under Re-circulating System

Fry monosex Nile tilapia ( Oreochromis niloticus ) were fed in five dietary protein levels (21%, 25%, 32% 37% and 45%) to investigate casual effects on growth performance, carcass composition and survival rate. Tests were carried out in 10 glass tank (50 x 25 x 40 cm) containers (50 L) of reticulating system maintained at 30 ± 1°C. At the beginning of tests, one hundred tilapia fry were randomly divided into five different groups with two replicates. Diets were fed to duplicate groups of ten fry with an initial weight of 1.25 ± 0.25 g/fish during 42 days. The results showed significant effects of dietary protein on growth performance of reared fish. Weight gain (WG) and Specific Growth Rate (SGR) increased significantly with increasing dietary protein levels between 32.38% and 37.63%. However, 45.5% of crude protein showed less important increase in growth parameters. The best Feed Conversion Rate FCR (1.26) was noticed in diet containing 37.63% of crude protein. Accordingly, higher survival rate (%) was recorded in fish fed on diets containing 32.38 and 37.63%. There was no significant difference in protein body content of tilapia fed on five diets as compared to the initial fish. Lipid body content increased significantly with high dietary protein levels from 21.88% to 45.50%. The carcass crude lipid was recorded as higher (9.4%) in the fry fed on diet containing 45.50% protein, followed by fish fed on diet having protein 21.88%. From results, diet containing 37.63% crude protein appears to be more suitable for monosex Nile tilapia growth, in related experience conditions. In this line, it is recommended to feed monosex tilapia fry.

Comparative Growth Performance of Mono-sex and Mixed-sex Nile Tilapia (<i>Oreochromis niloticus</i> L.) in Pond Culture System at Sebeta, Ethiopian

Comparative growth performance of hand-sexed male mono-sex and mixed-sex Nile tilapia ( Oreochromis niloticus ) was conducted in six earthen ponds (200 m 2 each) in semi-intensive culture system. Experimental ponds were stocked at a stocking density of 2 fish/m 2 . Fish were cultured for a period of 240 days and fed at a daily rate of 5% of fish body weight. The results of the experiment showed that male mono-sex tilapia showed significantly higher (P<0.05) growth rate (weight, length, DWG, SGR) than mixed-sex group. Generally, male mono-sex fishes reached a larger final individual size (176.20±18.01) g than mixed-sex ((108.20±15.4)g, P<0.05). This difference was more pronounced after the 6 th month during the culture period as the later started reproduction early in the production cycle. Analysis on the economic data indicated that both treatments showed positive net return for the culture periods of 6, 7 and 8 months. However, there was a difference in attaining the optimum net return in culturing Oreochromis niloticus as male mono-sex and mixed-sex. The male mono-sex group attained its optimum net return after 6 months of culture periods, while the mixed-sex group attained after 8 months. Therefore, culturing for extra two months in the later case showed a 32% decline from the optimum net return. Hence growing male mono-sex Oreochromis niloticus for 6 months is profitable under Sebeta, Ethiopia condition.

Effect Some Medicinal Plants Diets on Mono Sex Nile Tilapia (Oreochromis niloticus), Growth Performance, Feed Utilization and Physiological Parameters

Thirteen experimental diets containing 30% crude protein and 438.09 Kcal gross energy/100g were formulated to contain six different medical plants fenugreek meal (FM),Trigonella foenum-graecum; fenugreek sprouts meal (FSM); eucalyptus fresh leaves (EFL), Eucalyptus citriodora; hot pepper meal (HPM) Capsicum frutescens L. var. abbreviatum; thyme seeds meal (TSM) Thymus vulgaris and chamomile flowers meal (CFM), Matricaria recutita Lat three different levels (0.00; 1.00 and 2.00%) from each of such medicinal plant on the growth performance,feed utilization and whole body composition and physiological parameters of Nile tilapia Oreochromis niloticus fry. Fish were reared in twenty six glass aquaria with an average initial weight of 0.82 ± 0.3g/fish. The results of the present study illustrated that the averages of growth performance and feed utilization values as affected with medicinal plant sources indicate that FSM showed the highest growth performance and feed utilization values (P≤0.05) followed in a significant decreasing order by fenugreek meal (FM) and eucalyptus fresh leaves (EFL) then by hot pepper meal (HPM)and both Thyme meal (TM) and Chamomile flowers meal (CFM),respectively. Regardless of medicinal plants sources, The analysis of variance for medicinal plant levels (MPL) indicate that supplementation level of 1% revealed significant (P≤0.05) the highest growth performance and feed utilization values followed in a significant (P≤0.05) decreasing order by 0.00 and 2.00% level,respectively. Concerning the interaction between medicinal plants sources and their levels (0.00,1.00 and 2.00%) the highest growth performance and feed utilization values (P≤0.05) were obtained by group 1% FSM (diet No.4),while the lowest was recorded by the group 2% TSM (diet No.11).On the other hand, the interactions between medicinal plants sources and their levels observed the lowest total plasma protein(g/dl), total plasma lipid (g/dl), Hb (g/dl), Ht (%), AST (U/L), ALT (U/L) and uric acid concentrations (mg/dl) parameters were obtained by group 1% FSM (diet No.4),while the highest parameters were recorded by the 2% TSM (diet No.11). In general, and based on the obtained results it could be concluded that addition of 1% LMP to the diet which contain FSM is considered optimal for growth of mono-sex Nile tilapia,O. niloticus,fingerlings without any adverse effect on fish health.

Growth of Mixed-Sex and Monosex Nile Tilapia in Different Culture Systems

Growth of 17α-methyltestosterone treated monosex Nile tilapia, Oreochromis niloticus was compared with hormone untreated mixed-sex fish in four different culture systems. The experiment had 2 X 4 factorial design: the first factor was presence or absence of hormone treatment (monosex and mixed-sex fish), the second factor was related to culture system (cistern, flow-through, pen and pond). Fish were cultured under similar feeding regime and stocking density for six months and different growth parameters such as body weight, length, daily weight gain (DWG), specific growth rate (SGR), proximate body composition and survival rate were analyzed. Monosex tilapia showed significantly higher (P-value 0.05) among mixed-sex and monosex fish and between different culture systems. Monosex tilapia in pond culture system showed the highest weight, DWG and protein content while mixed-sex tilapia in cistern culture system showed the lowest weight, DWG and protein content. Considering the results of this study, culture of monosex tilapia in earthen ponds might be considered the ideal method for tilapia culture in India.

Effect of Stocking Density on Monosex Nile Tilapia Growth during Pond Culture in India

Effect of Stocking Density on Monosex Nile Tilapia Growth during Pond Culture in India

Polyculture of Nile Tilapia, Oreochromis niloticus, Either Confined in Cages or Unconfined in Freshwater Prawn, Macrobrachium rosenbergii, Ponds

Polyculture of Nile tilapia, Oreochromis niloticus, confined in cages suspended in prawn, Macrobrachium rosenbergii, ponds has been shown to reduce phytoplankton densities, pH levels, and increase prawn production when compared to prawn monoculture ponds. However, as filter feeders, tilapia grazing might be more efficient if allowed free access to all portions of the water column, positively impacting both phytoplankton control and tilapia growth. This study was designed to compare the effects of confined and unconfined tilapia, in polyculture with freshwater prawns, on prawn growth, tilapia growth, algae populations, and water quality. Juvenile prawns were stocked into each of nine, 0.04 ha ponds as 60 d nursed juveniles (0.8 ± 0.3 g) at 62,000/ha. Three control ponds contained only prawns (MONO). In three other ponds, monosex (male) Nile tilapia (89.2 ± 23.6 g) were stocked unconfined into three ponds at 4400/ha (POLY-UNC). In three additional ponds, the same size and number of tilapia were stocked but confined in two, 1 m3 cages at 100 fish/cage (POLY-CON). Prawns were fed a sinking pellet (28% protein) twice daily at a standardized rate for 114 d. Tilapia were fed a floating pellet (32% protein) twice daily to apparent satiation for 106 d. In the POLY-UNC treatment, average prawn harvest weight (26 g) and prawn production (1625 kg/ha) were significantly lower (P 0.05) between the MONO and POLY-CON treatments in terms of prawn harvest weight, production and feed conversion ratio with combined averages of 38 g, 2465 kg/ha, and 1.9, respectively. Average harvest weight and production of adult tilapia were not significantly different (P > 0.05) in the POLY-CON and POLY-UNC treatments averaging 485 g and 2293 kg/ha, respectively. Tilapia in the POLY-CON treatment had a significantly higher (P 0.05) among water quality variables or phytoplankton populations. Lower prawn production in the POLY-UNC is likely due to competition for food with the large number of tilapia juveniles. Despite the use of Genetically Modified Tilapia (GMT) monosex males, several cohorts of juvenile tilapia were produced in each of the POLY-UNC ponds, resulting in over 2500 kg/ha of juveniles in the POLY-UNC treatment. No wild spawn tilapia juveniles were found in the POLY-CON ponds. In summary, confinement of tilapia in cages appears preferable when tilapia are polycultured with freshwater prawn.

Effect of fresh or dried garlic as a natural feed supplement on growth performance and nutrients utilization of the Nile Tilapia (Oreochromis niloticas)

he present investigation aimed to study the effect of dietary fresh or dried garlic (Allium sativum) supplementation in the Nile tilapia (Oreochromis niloticus) diets at different levels, on growth performance, nutrients utilization,carcass traits and whole bodies' chemical composition. The study was performed in four concrete ponds (7.5 × 2.25 × 0.70 m). All experimental ponds were divided into four partitions with a water volume of each partition of 3 m3 (1.875 × 2.25 × 0.70 m). The experiment included five dietary treatments i.e the control (C); treatment 2 fed on the basal diet supplemented with 5g. fresh garlic/kg diet (FG5); treatment 3 supplemented with fresh garlic at 3g/kg (FG3) and treatments 4 and 5 supplemented with dried garlic at levels of 5 and 3g/kg (DG5) and (DG3), respectively. Fresh and dried garlic were supplemented to the basal diet and mixed with the basal diet thoroughly. Each dietary treatment was applied in triplicates and stocked with healthy mono-sex Nile tilapia fry (0.26g initial weight) at a rate of 60 fry each replicate i.e 20 fry / m3. The basal diet was formulated to contain about 33% crud protein and 4500 kcal gross energy. The experimental diets were fed at daily rates of 30; 10; 6 and 4% of the fish biomassfor fish weights from 0.26 to 1g; 1-5g; 5-20g and 20g till the end of the experiment after 22 weeks, respectively. The experimental diets were offered daily in equal parts at 9am; 11am; 1pm and 3pm, respectively.Results obtained are summarized in the following:1- The highest (P<0.05) final weights (90.02g); total weight gain (89.76g); dailyweight gain (0.58g); specific growth rate (3.81) and survival rate 93.89% wererecorded with the group fed on the basal diet supplemented with fresh garlic at3g/kg level, while the lowest value (P<0.05) was recorded by the control unsupplementedgroup. All garlic supplemented groups recorded significantlyhigher condition factor compared to the control group.2- The group fed on the diet supplemented with dried garlic (5g/kg) recordedsignificantly the best feed conversion ratio; protein efficiency ratio and proteinproductive value; while the control group recorded the worst value of the testedfeed utilization parameters.3- Garlic supplementation of Nile tilapia diets released significant effects ondressing percentages for the favor of dried garlic at levels 5 and 3g/kg while the control group recorded the lowest (P<0.05) value, garlic supplementationshowed significant effects on by-products; flesh percentages and hepato somaticindex.4- Supplementation of Nile tilapia diets with fresh or dried garlic had nosignificant effects on moisture; dry matter and ash contents of fish whole bodies,while it released significant effects on the whole body protein and fat comparedto the control group.5- Dietary fresh or dried garlic supplementation showed significant effects ontilapia serum total protein; total albumen; total globulin and total lipids.6- Supplementing Nile tilapia diets with fresh garlic at levels of 5 or 3g/kg anddried garlic at levels of 5 or 3g/kg reduced the costs of production one kg of fishgain by 6.39; 6.02; 9.72 and 6.05% compared to the control group, respectively.Based on the present results, supplementation of growing Nile tilapia dietswith dried garlic at 5g/kg diet level is recommended to achieve better growthperformance; feed utilization and to reduce the costs of production of onekg/gain in weight.

Comparative Growth Performance of Mixed-Sex and Monosex Nile Tilapia Population in Freshwater Cage Culture System under Indian Perspective

Cage culture is one of the important methods for intensive culture of tilapia in large water impoundments. But,information related to growth performance of androgen-treated monosex tilapia population during cage culture underthe ecological conditions of India is limited. The aim of this study was to compare the growth potential of control,mixed-sex and androgen-treated, monosex tilapia in confined environment of cages. Control and hormone treated fishwere stocked separately in mesh cages at a density of 50 fry / m3 and it was found that the androgen treated monosexfish grew significantly larger than their control mixed-sex counterparts. The monosex population showed a significantlyhigher weight, length, depth, specific growth rate, daily weight gain, protein efficiency ratio and body protein contentthan the mixed-sex tilapia population. Thus, culture of hormone treated monosex tilapia in cages can be consideredideal for augmented production of the fish under Indian context.

Effect of replacing soybean meal protein with jojoba seed meal in diets of growing mono-sex Nile tilapia (Oreochormis niloticus) on growth performance and nutrient utilization

he study aimed to investigate the effect of replacing soybean meal (SBM) protein by treated Jojoba seed meal (JSM) in diets of Nile tilapia (Oreochromis niloticus) on growth performance, nutrient utilization, carcass traits, body chemical composition and digestibility of nutrients of Nile tilapia, reared under semi-intensive conditions in fiber glass tanks. The experimental tanks (1m x 2m x 0.5m) each contains one m 3 water volume, were used in this study. The three tanks represented three dietary treatments, the first tank served as a control, where the experimental fish were fed on the control diet containing soybean meal (SBM) as a source of plant protein with fish meal as a source of animal protein. Fish of the second and third tanks were fed on diets containing the Jojoba seed meal (JSM) to replace 25 and 50% of SBM protein, respectively. The experimental tanks were stocked with Nile tilapia fingerlings at a density of 50 individuals in each tank. The experimental period lasted 18 weeks after start. The initial weight of the experimental fish ranged between 7.20 ± 0.09 g and 7.5 ± 0.08 g and they were allotted randomly into the experimental tanks. The experimental rations contained 30% crude protein and 4500 kcal gross energy/ kg diet and the experimental diets were formulated to be almost isonitrogenous isocaloric. The experimental diets were fed at a rate of 3% of tank fish biomass 6 days a week, in two portions, at 9:00 a.m. and 3:00 p.m. The results of this study revealed that, the highest (P<0.05) final weights, specific growth rate, protein and nutrient utilization were recorded by JSM 25% group followed by the control group and the JSM 50% groups, respectively. The same trend was observed in apparent digestibility coefficients. Therefore, these results suggest that up to 25% of soybean meal can be replaced by treaded Jojoba seed meal protein in Nile tilapia diets without any adverse effect on growth performance, feed and protein utilization, body composition and digestibility of nutrients.

PARTIAL REPLACEMENT OF SOYBEAN MEAL WITH BLACK SEED AND ROQUETTE SEED MEALS IN NILE TILAPIA (Oreochromis niloticus) FINGERLINGS DIETS.

Black seed meal (Nigella sativa) and roqutte seed meals (Eruca sativa) were tested to replace soybean meal (SBM) in diets for mono sex Nile tilapia fingerlings (Orecreomis niloticus). Nine isonitrogenous (30% CP), isocaloric (460 kcal GE/100g) diets were formulated to contain black seed (BSM) and roquette seed meals (RSM) as a partial replacement of soybean meal at different levels (0, 5, 10, 15 and 20%) forming 9 treatments, 4 with BSM and 4 with RSM and the control. The diets were fed daily at a rate of 4 % of fish body weight in triplicate groups with 15 Nile tilapia fingerlings each (3.14g/fish), in 80 l glass aquaria for 90 days period. Data collected were on growth rate, feed utilization and body composition along with simple economic evaluation. Results of growth performance showed that SBM substitution with BSM and RSM were nearly similar. Survival rate was not affected greatly but it seems that all levels of BSM substitution were more favorable than the other RSM substitutions. As for feed utilization most treatments used showed similar results to the control. The 20 % RSM replacement (instead of SBM) showed the lowest values. Carcass CP content was not affects by all levels of BSM and 5 to 15% levels of RSM that substituted SBM. Carcass fat content showed no significant differences among all groups and the control group. The highest ash content in fish body was obtained by fish fed T9 diet which contained 20% RSM as a partial replacement of SBM. The present study suggest that BSM and RSM have were more economic efficiency when replacing SBM at levels of 20% and 15%, respectively in Nile tilapia fingerlings diets.

Effect of Dietary Protein Levels on Growth Performance and Body Composition of Monosex Nile Tilapia, Oreochromis niloticus L. Reared in Fertilized Tanks

Effect of Dietary Protein Levels on Growth Performance and Body Composition of Monosex Nile Tilapia, Oreochromis niloticus L. Reared in Fertilized Tanks

Effect of initial weight and stocking density on growth performance of mono sex nile tilapia reared in semi intensive system

he present investigation was carried out at Wady El Raian, Fayoum Governorate, Egypt in order to test the effects of initial weight and stocking density on growth performance and pond productivity of Nile tilapia (Oreochromis niloticus) in semi intensive system. The experiment was carried out in 12 earthen ponds each of a total area of one feddan (4200 m 2 ) to represent six treatment groups in replicates each. The first; second and third two ponds (T1; T2 and T3) were stocked with Nile tilapia fingerlings of an average initial weight of 9.6 g and stocking density 30; 40 and 50 thousands respectively. The second; fourth and sixth tow ponds (T4; T5 and T6) were stocked with Nile tilapia fries of 0.3g and stocking density 30; 40 and 50 thousands respectively. The fish were fed three times daily on a commercial diet containing 27% protein at a rate of 3% of fish biomass. The experiment lasted for 26 weeks from the start. Results obtained are summarized in the following: 1- Water quality (physical and chemical) lied within the permissible levels required for optimum growth and development of Nile tilapia. 2- The highest final weight was obtained by T4; T1; T2; followed in a significant decreasing order by T5; T4 and T6 respectively. 3- Averages of gain in weight; daily gain; specific growth rate and condition factor were influenced significantly with tilapia initial weight and stocking density. 4- Total fish production/feddan was the highest for 50 thousand fingerlings/feddan, stocking density followed by 40 and 30 thousand fingerlings/feddan. 5- The highest net returns were by the 30 thousand fingerlings/feddan stocking density (T1) and 40 thousand fingerlings/feddan stocking density (T2) due to the high contribution of super size and grade 1 fish in the harvest, compared to other densities and initial weights.

Nutrition evaluation of sesame seed meal, Sesamum indicum (L.) as alternative protein source in diets of juvenile mono-sex Nile tilapia (Oreochromis niloticus).

he main objective of this study was to evaluate the effect of partial and total replacement of fish meal protein by sesame seed meal (SSM) protein in commercial diets on growth performance, feed utilization and bodycomposition of juvenile mono sex Nile tilapia, Oreochromis niloticus (L.). Fish of an average initial weight of 0.60 ± 0.01 g were stocked in 15 glass aquaria (80 l each) at a rate of 15 fish per aquarium. Fish meal protein (18% of the diet) wasused as the sole source of animal protein in the control diet. Percent replacements of fish meal by sesame seed meal on the basis of crude protein were as follows: 0 % (control diet A), 25 % (diet B), 50 % (diet C), 75 % (dietD) and 100 % (diet E). All tested diets were almost isonitrogenous and fed at a rate of 4 % of fish body weight, and then gradually reduced to 3 % of the total fish biomass daily, for a period of 16 weeks. The results of this study revealedthat, fish fedon diet A (100 % FM) had the highest average body weight, specific growth rate (SGR), weight gain %, feed conversion ratio (FCR), and protein efficiency ratio (PER), but the lowest was obtained with fish fed diet E (100 %SSM). The same parameters of fish fed on diets B (25 % SSM) and diet C (50 % SSM) were not significantly different (P > 0.01) from those of fish fed on the control diet A. Proximate composition of the whole body moisture and ashcontents were not significantly affected (P>0.05) by the dietary treatments.Whole body protein contents for fish fed on diets B, C and D were superior to the control diet. Incorporation of sesame seed meal in the fish diets increasedsignificantly whole body fat content. Incorporation of sesame seed meal in the diets significantly increased apparent digestibility coefficients of crude protein, crude fat and energy. Therefore, these results suggest that up to 50 % of fishmeal protein can be replaced by sesame seed protein in mono sex Nile tilapia diets without any adverse effect on growth performance and feed utilization,body composition and digestibility.

Subacute Intoxication of a Deltamethrin‐Based Preparation (Butox® 5% EC) in Monosex Nile Tilapia, Oreochromis niloticus L.

The monosex Nile tilapia, Oreochromis niloticus L., was exposed to subacute concentration (1.46 microg/l) of a pyrethroid insecticide, deltamethrin for 28 consecutive days. Behavioural, clinical, haematological, serum biochemical and histopathological consequences were assayed at a regular interval of 7 days. The abnormal behavioural responses and toxic symptoms were described. Exposure to deltamethrin not only significantly decreased lymphocyte and basophile percentages, total leucocytic and total erythrocytic counts, haemoglobin percentage and packed cell volume value, but also caused serious effects in the form of hypoproteinaemia, hypoalbuminaemia, hypercholesterolaemia, hyperglycaemia and significantly increased serum aspartate aminotransferase, alanine aminotransferase and alkaline phosphatase activities. Moreover, the histopathological results indicated that the haemobiotic organs were affected by deltamethrin, primarily liver and gills. Our data suggest that subacute exposure to deltamethrin exerts a serious metabolic distress on the fish corresponding to the exposure period. In addition, the assayed parameters and histopathological findings can be as good biomarkers of pyrethroid ecosystem pollution.

Effects of Two Densities of Caged Monosex Nile Tilapia, Oreochromis niloticus, on Water Quality, Phytoplankton Populations, and Production When Polycultured with Macrobrachium rosenbergii in Temperate Ponds

Abstract The effects of different densities of caged Nile tilapia, Oreochromis niloticus, on water quality, phytoplankton populations, prawn, and total pond production were evaluated in freshwater prawn, Macrobrachium rosenbergii, production ponds. The experiment consisted of three treatments with three 0.04‐ha replicates each. All ponds were stocked with graded, nursed juvenile prawn (0.9 ± 0.6 g) at 69,000/ha. Control (CTL) ponds contained only prawns. Low‐density polyculture (LDP) ponds also contained two cages (1 m3; 100 fish/cage) of monosex male tilapia (115.6 ± 22 g), and high‐density polyculture (HDP) ponds had four cages. Total culture period was 106 d for tilapia and 114 d for prawn. Overall mean afternoon pH level was significantly lower (P ≤ 0.05) in polyculture ponds than in CTL ponds but did not differ (P &gt; 0.05) between LDP and HDP. Phytoplankton biovolume was reduced in polyculture treatments. Tilapia in the LDP treatment had significantly higher (P ≤ 0.05) harvest weights than in the HDP treatment. Prawn weights were higher (P ≤ 0.05) in polyculture than prawn monoculture. These data indicate that a caged tilapia/freshwater prawn polyculture system may provide pH control while maximizing pond resources in temperate areas.

Economic profitability of Nile tilapia (Oreochromis niloticus L.) production in Kenya

Economic profitability of Nile tilapia production in Kenya was analysed using a model that simulated individual fish growth and took fish population dynamics in the pond into account. The results suggest that the currently practiced mixed-sex tilapia culture is economically unsustainable. It is suggested that research and extension efforts be geared towards developing monosex Nile tilapia production systems. Nile tilapia culture with African catfish predation should be viewed as an intermediate step towards all-male Nile tilapia culture. This will allow accumulation of both physical and human capital to support all-male tilapia culture. Under all-male culture, economic returns are high enough to justify investment in Nile tilapia culture using borrowed capital. However, the success of monosex culture will depend on the availability and affordability of quality fingerlings and low-cost fish feeds. The results have a wide application in Sub-Saharan Africa where mixed-sex Nile tilapia culture is common.

Acute intoxication of deltamethrin in monosex Nile tilapia, Oreochromis niloticus with special reference to the clinical, biochemical and haematological effects

Deltamethrin, a synthetic pyrethroid pesticide, potential toxic pollutant and significant direct risk to the aquatic ecosystems, was investigated in the present study for its toxic impact on adult monosex Nile tilapia on the basis of acute static bioassay test, and comparison of clinical, biochemical and haemato logical examinations with deltamethrin-free control group. The 96 hLC 50 value of deltamethrin for monosex tilapia was 14.6 μg/L. The abnormal behavioral responses and toxic symptoms were described. Fish exposed to the higher deltamethrin concentration (15 μg/L) for 96 h showed significantly higher lymphocytes, total leucocytic and erythrocytic counts, haemoglobin percentage and packed cell volume content and significantly lower neutrophils compared to the control group. Deltamethrin caused adverse effects in the form of hypoproteinemia, hypoalbuminemia, hypercholesterolemia, hypoglycemia and significant increase of serum aspartate aminotransferase, alanine aminotransferase, and alkaline phosphatase activities. The results provide evidence that deltamethrin pollution may have adverse impacts and was highly toxic to monosex tilapia.

Impact of nutrition and season on pond culture performance of mono-sex and mixed-sex Nile tilapia ( Oreochromis niloticus)

A 2×2×2 factorial experiment was carried out in a 16 earthen pond system to determine the effect of poor and improved nutrient inputs on the performance of mixed-sex and mono-sex Nile tilapia over both wet and dry seasons in Central Thailand. The poor nutrient level consisted of fresh ruminant manure only (50 kg dry matter ha −1 day −1) and the improved also received inorganic fertilisers and ricebran as supplementary feed. Artificially incubated first feeding hatchlings were nursed under similar conditions to produce mixed-sex and mono-sex fry before stocking in 200 m 2 ponds at 3 fish m −2. Growth and net yields after 5 months were affected by nutrient level but not by sex (mono- or mixed-sex). However, ponds stocked with mixed-sex fish had a significantly greater proportion of small fish (<15 cm TL) than mono-sex that had more large size class fish (>15 cm TL). Mean weights of fish in each size class were not different overall but if ponds with improved nutrition were considered alone, survival and use of mono-sex affected the mean size of recruits (i.e. individuals <10 cm) and stocked fish (10–20 cm) harvested. Individual harvest size was inversely related to survival. The lack of major differences in performance of mono-sex and mixed-sex was linked to the presence of piscivorous fish and the method of seed production. The pattern of survival among the different treatments was possibly related to the movement of the air-breathing fish between ponds. The homogeneous and young age of the mixed-sex seed may explain the relatively low levels of reproduction, indicated by numbers of fry, observed in the trial. The importance of nutrient levels, rather than the use of mono-sex fish in the Chitralada strain, was demonstrated, provided young mixed-sex seed are used. The study has implications for promoting smallholder tilapia production; both the nature of demand for fish and the resource base need to be understood before developing tilapia hatchery strategies.