Final Individual Weight Research Articles

Growth performance and stress response of common sole subjected to varying stocking densities and rearing temperatures

Earlier short-term studies have shown productivity of intensively farmed common sole (S. solea) to be closely dependent on rearing density. Irrespective of fish size, elevating crowding conditions led to declining growth rates while the effect of density on mortality remains controversial. To what extent water temperature could affect productivity of growing sole subjected to varying crowding conditions, warrants investigation as very few studies have tried to quantify the effects of this fundamental rearing parameter on growth and survival in this fish species. This is particularly crucial for developing suitable farming protocols in Italy, where common sole may experience a broad range of water temperatures throughout the rearing cycle. The aim of this study was to evaluate productivity and blood cortisol level as a measure of stress response, in growing sole subjected to different stocking densities and temperature conditions. Six hundred juveniles (ind. weight 21.8±1.5g) were randomly allotted among eight groups kept in 0.38m2 (0.1m3) rectangular vessels, according to a factorial design combining two stocking densities (D, 150 vs 300ind/m2; i.e. 3.3 vs 6.5kg/m2) and two rearing temperature ranges (T, 18-20 vs 22-24°C) with duplicate groups per treatment. Fish were fed over 148 days an extruded dry diet distributed at 1% biomass/d in two meals. After 32 and 134 days on trial, blood samples were obtained after caudal puncture from five specimens per group. Plasma cortisol levels were analysed by EIA. Growth performance, survival, feed conversion rate (FCR) and productivity (biomass gain/m2/d) were calculated per group at the end of the trial. All response variables were subjected to a twofactor ANOVA. No significant interaction was found between main factors for the various response parameters. The different rearing temperature did not affect (p>0.05) growth performance (final individual weight, 59±11g, specific growth rate, 0.67±0.11%d-1), survival (83.5±11%), FCR (1.6±0.2), productivity (35.5±5.8g/m2/d) or plasma cortisol levels (6.6±0.5ng/ml). Doubling the initial stocking density resulted in reduced growth (final weight, 49 vs 68.5g; specific growth rate, 0.59 vs 0.75, p<0.05), lower survival (76 vs 91.3%, p<0.05) and impaired FCR (1.8 vs 1.4, p<0.05). On the opposite, productivity was significantly improved at the higher density (39.1 vs 31.8g/m2/d) while plasma cortisol levels were unaffected by crowding. The results here obtained confirm a density-dependent growth performance in sole which appears unrelated to rearing temperature. Plasma cortisol levels did not suggest rearing density or water temperature to be chronic stressors within the range of values here investigated. In this study, sole was shown to be able to adapt to a wide range of intensive culture conditions. This could provide clues on possible farming strategies aimed at promoting fast growth and/or high productivity by modulating stocking density.

Glass eels (Anguilla anguilla) growth in a recirculating system

On a commercial eel farm, which uses a recirculation system, 400,000 glass eels were farmed for a period of 328 days at 20o – 23o C. The physicochemical parameters of the farm water were kept at normal conditions during the experiment. The NO 2 was kept between 1.0 and 3.0 mg/l. By the end of the experiment, 4,582 kg of fish feed were consumed and 2,939 kg of eels were produced (177,523 eels with mean final individual body weight of 16.6g and mean food conversion ratio of 1.625). The glass eels showed a high variability in their capacity to grow.

Growth, Processing Measurements, Tail Meat Yield, and Tail Meat Proximate Composition of Male and Female Australian Red Claw Crayfish, Cherax quadricarinatus, Stocked into Earthen Ponds

Small (0.7 g) juvenile red claw, Cherax quadricarinatus, were stocked in earthen ponds (0.04 ha) in Kentucky and grown for 86 days so that measures of growth, survival, processing characteristics, and proximate composition of tail muscle in male and female Australian red claw crayfish could be obtained. A commercial marine shrimp was fed to all red in two separate feedings, each consisting of one-half of the total daily ration between 0800-0830 and between 1530-1600 hours for the duration of the culture period. Total weight and number of red claw from each pond were recorded at the harvest. Forty red claw from each sex were randomly sampled, chill-killed by lowering the body temperature in an ice-bath, and frozen (-20°C) for processing measurements and proximate composition. Red claw were removed from the freezer, thawed, individually weighed to the nearest 0.01 g, and then were hand-processed so that weights of chelae, tail, and tail muscle were obtained to the nearest 0.01 g. After 87 days, red claw had a final average individual weight of 59.6 g, weight gain of 8,413%, survival of 64.0%, yield of 903 kg/ha, and feed conversion ratio (FCR) of 4.63. When analyzed by sex, males had significantly (P < 0.05) higher final individual weight (71.05 g) compared to females (53.65 g); higher (P < 0.05) chelae weight (13.1 g for males compared to 6.84 g for females); higher tail weight (25.53 g for males compared to 20.38 g for females); higher tail muscle weight (18.99 g for males compared to 14.89 g for females); and higher cephalothorax weight (32.41 g for males compared to 26.44 g for females; Table 2). There were no significant differences (P > 0.05) in the percentage moisture, protein, lipid, fiber, and ash in the tail muscle of male and female red claw when analyzed either on a wet-weight basis and averaged 81.0%, percentage protein averaged 16.46%, percentage lipid averaged 0.16%, fiber averaged 0.1%, and percentage ash averaged 1.42%. Results from the present study indicate that red claw can be grown as a commercial aquaculture species in locations with limited growing seasons, and that male red claw grow larger, have larger chelae, and higher tail muscle weights compared to females so that it might be economically advantageous to stock all-male populations of red claw in ponds to achieve maximum production. Further research on growth and processing yields of red claw should be conducted to assist the industry.

On-farm and on-station comparison of wild and domesticated Cameroonian populations of Oreochromis niloticus

Wild (Sanaga River) and domesticated populations of Oreochromis niloticus were compared on-farm and on-station in the Central Province of Cameroon to determine the degree to which genetic deterioration of stocks may have occurred during the process of domestication and subsequent breeding. On-station, average weight at harvest was 284.3±16.2 and 178.1±9.9 g for Sanaga and domesticated populations, respectively. On-station specific growth rate was 0.0660±0.0022 and 0.0555±0.0016 g/day for Sanaga and domesticated populations, respectively. On-station standing stock at harvest was 5747.3±624.4 and 4170.3±233.4 kg/ha for Sanaga and domesticated populations, respectively. Differences in average weight at harvest and specific growth rate on-station are significant at P<0.003. Differences in standing stock at harvest on-station are significant at P<0.015. On-farm, average weight at harvest was 121.1±26.5 and 87.5±17.2 g for Sanaga and domesticated populations, respectively. On-farm specific growth rate was 0.0442±0.0057 and 0.0358±0.0047 g/day for Sanaga and domesticated populations, respectively. On-farm standing stock at harvest was 2454.2±445.6 and 1667.8±352.2 kg/ha for Sanaga and domesticated populations, respectively. Differences in average weight at harvest on-farm are significant at P<0.05. Differences in specific growth rate on-farm are significant at P<0.04. Differences in standing stock at harvest on-farm are significant at P<0.015. The Sanaga River population consistently out-performed the domesticated population. Final individual weight of domesticated fish averaged 39% less than wild fish on-station and 42% less than wild fish on-farm.

A Preliminary Assessment of Growth, Survival, Yield, and Economic Return of Australian Red Claw Crayfish, Cherax quadricarinatus, Stocked at Three Densities in Earthen Ponds in a Cool, Temperate Climate

Juvenile (mean weight 8.1 g) Australian red claw crayfish, Cherax quadricarinatus, were stocked in July at three rates of 12,000/ha, 18,000/ha, and 24,000/ha into two, 0.02-ha earthen ponds in a cool temperature region of the United States (Kentucky) and grown for 70 days. Red claw were fed a pelleted marine shrimp diet twice daily. Ponds had continual aeration provided. Dissolved oxygen and temperature were measured twice daily (0900 and 1530 hours); total ammonia nitrogen (TAN), nitrite, and alkalinity were measured twice weekly; and pH was measured daily. At harvest, there were no significant (P > 0.05) differences in final individual weight, percentage weight gain, specific growth rate, feed conversion ratio, percentage survival, yield, and economic return among all treatments and averaged 58.4 g, 805%, 3.04%/ day, 7.47,42.7%, 461 kg/ha, and -$2659/ha, respectively. There were no significant (P > 0.05) differences in the percentage of males and females harvested from the ponds among any stocking rate with males comprising 48.2% and females comprising 51.8%. Final individual weight of males and females was not significantly (P > 0.05) different among all treatments. These data indicate that there is no advantage to stocking red claw at rates below 24,000/ha in terms of growth, survival, yield, and economic return and that red claw can grow to marketable size in a cooler temperate region of the United States with a short (<110 days) growing season by stocking a larger-size (8 g) red claw.

Growth of redclaw crayfish Cherax quadricarinatus (Von Martens 1868) (Decapoda: Parastacidae) juveniles fed isoproteic diets with partial or total substitution of fish meal by soya bean meal: preliminary study

Growth of juvenile redclaw Cherax quadricarinatus fed 400 g kg−1 crude protein isoproteic diets substituting fish meal with soya bean meal at various levels (250, 500, 750 and 1000 g kg−1) was evaluated under laboratory conditions. Juvenile crayfish were reared individually in 1-L plastic containers for 56 days. Total survival was recorded for all treatments at the end of the experiment. There were no significant differences (P > 0.05) for the specific growth rate among the treatments, although the animals fed with the control diet (100% fish meal) obtained the highest mean daily weight gain (0.055 g day−1), individual final weight (4.12 g), molts per individual (0.04 molts day−1) and molting frequency (23.57 days) values at the end of the experiment. Dietary inclusion of soya bean meal at the tested levels hampered the C. quadricarinatus juvenile growth.

Potato protein concentrate with low content of solanidine glycoalkaloids in diets for Atlantic salmon ( Salmo salar)

Previous testing of standard potato protein concentrate (PPC) in salmonid diets resulted in severe appetite loss. This has been attributed to the solanidine glycoalkaloids (SGA) in the PPC, among which α-solanine and α-chaconine are the best known. The present study investigated the nutritional value of a PPC with reduced SGA content (SGA<100 μg g −1) as a partial fish meal (FM) substitute in diets for Atlantic salmon. FM and wheat were replaced by low-SGA PPC in increments, producing four extruded diets containing 0%, 7%, 14%, and 21% PPC. Each diet was fed to triplicate groups of 82 g salmon maintained in 8–13 °C seawater. The experiment lasted 84 days, divided into three periods. Appetite, feed conversion, and retention of N and energy were not affected by dietary treatment. All groups of fish grew to final individual weights ranging 249–256 g. There were no significant differences in apparent macronutrient or amino acid digestibility among groups fed different diets. In conclusion, low-SGA PPC is well suited for partial FM substitution in salmon diets.

Complete Replacement of Fish Meal by Soybean Meal with Dietary L‐Lysine Supplementation for Nile Tilapia Oreochromis niloticus (L.) Fingerlings

AbstractThe effect of complete replacement of fish meal by soybean meal (SBM) with the dietary L‐lysine supplementation in prepared diet was studied in Nile tilapia fingerlings. Five isonitrogenous (33.2% crude protein) and isocaloric (4.8 kcal gross energy/g of diet) diets were formulated. Diet 1 was similar to a high quality commercial tilapia diet, containing 20% fish meal and 30% SBM. Diets 2–5 contained 55%, 54%, 53%, and 52% SBM and 0.5%, 1.0%, 1.5%, and 2.0% L‐lysine supplementation, respectively. After 10 wk, there was a significant difference in the final individual weight, final body length (cm), weight gain (%), specific growth rate (SGR), feed conversion ratio (FCR), protein effkiency ratio (PER), and food intake among flsh groups (P≤ 0.05). The best bal individual weight, final individual length (cm), weight gain (%), specific growth rate, feed conversion ratio, protein efficiency ratio (PER), and food intake were recorded in fish fed diet 2, which contained 55% SBM and 0.5% L‐lysine. There was a significant difference between it and diet 1 (control). Moisture in fish flesh was not significantly different (P &gt; 0.05) among treatments and averaged 75.13%, while percentage protein was significantly dltrerent (P≤ 0.0% and the best result was achieved in flsh fed diet 2 and diet 1 (control). The highest values of digestibility coefficients of protein, fat and energy were recorded in groups of fish fed diet 2. These suggest that a diet with 55% SBM supplemented with 0.5% L‐lysine can totally replace fish meal in a diet for Nile tilapia fingerlings, without adverse effect on fish performance.

Effects of dietary carnitine and protein energy:nonprotein energy ratios on growth, ammonia excretion and respiratory quotient in African catfish,Clarias gariepinus(Burchell) juveniles

Two separate feeding experiments were carried out to determine the effects of dietary carnitine supplements on growth rates, total ammonia nitrogen (TAN) excretion and respiratory quotient rates (RQ) in the African catfish, Clarias gariepinus (Burchell), juveniles fed various diets differing in protein energy:nonprotein energy ratio (PE:NPE). In Experiment 1, 540 fish (20.9 ± 1.0 g) were evenly distributed into six dietary groups and fed in duplicate aquaria (N = 12 aquaria) to apparent satiation over a 41-day period, until all fish attained an individual final weight of 156.9 ± 10.8 g. Diets were formulated to contain two levels of carnitine (80 and 660 mg kg−1) and three levels of PE:NPE (0.7, 0.9 and 1.4). Sampling was divided into two size ranges, according to the predicted individual end-weight of 60 g (days 0–16) and 160 g (days 16–41). In Experiment 2, 240 fish (16.5 ± 0.2 g) were distributed in four 140-L aquaria connected to a respirometer and preconditionally fed twice a day at a restricted feeding level of 24 g kg−0.8 day−1 for a 25-day period (final weight of 77.5 ± 1.5 g). Four isonitrogenous diets (368 g kg−1 crude protein) were formulated to contain two levels of fat (85 and 175 g kg%−1) and two levels of carnitine (40 and 600 mg kg−1), in a 2 × 2 factorial design. From days 20–25, three respirometric trials were carried out, during which total ammonia nitrogen (TAN) and RQ were determined over 24 h. In both experiments, carnitine supplemented fish accumulated 2.5−4 times more carnitine in their tissues than fish fed a basal level (P < 0.05). In Experiment 1, the smallest fish (<60 g) fed 660 mg carnitine showed significantly higher growth rates and lower feed conversion rates than 80 mg carnitine supplemented fish only when the dietary PE:NPE ratio was low (0.7). Additionally, dietary carnitine significantly increased protein:fat ratios in the whole body, suggesting a protein-sparing action. In Experiment 2, high carnitine supplements decreased both TAN excretion and RQ rates in fish <80 g.

Estimating digestible protein requirements of silver perch, Bidyanus bidyanus Mitchell

In this study, we estimated requirements for digestible protein, using intact protein sources, at one digestible energy content. Using digestibility data for silver perch (Bidyanus bidyanus Mitchell) for a large number of ingredients, we formulated a ‘summit’ diet to contain between 1.4 and 1.8 times the ‘expected requirements’ for digestible essential amino acids (based on requirements for channel catfish, Ictalurus punctatus Rafinesque). A ‘diluent’ diet was formulated to contain 0.4–0.5 times the expected requirements of digestible essential amino acids. Both ‘summit’ and ‘diluent’ diets contained similar digestible energy (14.7 MJ digestible energy kg−1 for the summit and 13.4 MJ digestible energy kg−1 for the diluent). Six diets were prepared with the following amounts of summit–diluent diets: 100:0, 80:20, 60:40, 40:60, 20:80 and 0:100. A practical diet widely used by commercial farmers was also included as a control. Ten juvenile fish (2.1–2.6 g) were stocked into each experimental 70-L acrylic aquarium, and each dietary treatment was randomly assigned to five replicate aquaria. Fish were fed twice daily to apparent satiation for 54 days. Final individual fish weight ranged from 4–15.5 g. Results were analysed using intersecting linear regression analysis. The optimum digestible dietary protein for diets with 13.4–14.7 MJ digestible energy kg−1, after which protein deposition did not increase significantly, was 28%. Although this study did not determine requirements for individual amino acids, for diets with the digestible energy content used here, requirements for individual amino acids obviously did not exceed the content in the 28% protein diet. These contents are useful as an estimate of ‘recommended levels’ for silver perch diets with 13.4–14.7 MJ digestible energy kg−1. The proximate composition of fish was affected by diet. Whole body protein and moisture increased, whereas lipid content decreased with increasing dietary protein content (and increasing protein–energy ratio and decreasing lipid). Fish size was also affected by diet; however, the changes in whole carcass proximate composition also occurred for fish fed diets 60:40, 80:20 and the summit diet which were a similar final weight.

Efeito de períodos de cultivo e densidades de estocagem sobre o desempenho do catfish (Ictalurus punctatus) nas condições climáticas do litoral de Santa Catarina

Foram realizados dois experimentos com o objetivo de estudar o efeito do período de cultivo e da densidade de estocagem sobre o crescimento de juvenis de catfish, Ictalurus punctatus. No primeiro experimento, em delineamento estatístico fatorial inteiramente casualizado, estudaram-se os efeitos de duas densidades de estocagem (0,5 e 0,75 peixes/m²) e de dois períodos de cultivo subseqüentes (com cinco e quatro meses de duração, respectivamente). No segundo experimento, compararam-se duas densidades de estocagem(0,5 e 0,75 peixes/m²) em um período de cultivo equivalente ao somatório dos dois períodos de cultivo do primeiro experimento. No primeiro experimento, houve efeito estatístico significativo para períodos quanto ao ganho de peso individual, peso médio, biomassa final e ganho de biomassa. Foi observado efeito de densidade de estocagem quanto à biomassa final e ganho de biomassa, não havendo efeito interativo entre as duas variáveis estudadas. O peso individual final e ganho de peso no período de cinco meses de cultivo, com densidades de 0,50 e 0,75 peixes/m², foram de 608,1 e 531,4 g e 550,2 e 473,5 g, respectivamente, e no período subseqüente de quatro meses, de 274,2 e 188,3 e 211,3 e 182,3 g, respectivamente. Para biomassa final e ganho de biomassa, os valores observados no período inicial foram, respectivamente, de 298,0 e 262,1 e 397,9 e 354,5 g/m², e no período subseqüente, de 132,9 e 89,9 e 179,9 e 119,9 g/m², respectivamente. No segundo experimento, não houve efeito estatístico significativo para os parâmetros estudados; os valores de peso individual final, ganho de peso, biomassa final e ganho de biomassa foram, respectivamente, para as densidades de 0,50 e 0,75 peixes/m², 941,1 e 758,1; 885,1 e 701,2; 491,7 e 587,1; e 463,1 e 535,4 g/m². A sobrevivência média foi de 98% e os parâmetros físico-químicos da água mantiveram-se dentro da normalidade. Concluiu-se ser viável a produção do Ictalurus punctatus nas condições climáticas em que foi conduzido o estudo.

Fertilization, hatching, survival and growth rates in reciprocal crosses of two strains of an African catfish Heterobranchus longifilis Valenciennes 1840 under controlled hatchery conditions

A diallelic cross between two strains [Layo strain (LS) and Noun strain (NS)] of the catfish Heterobranchus longifilis Valenciennes was carried out under controlled hatchery conditions to estimate their reproductive performance and aquaculture potential in terms of fertilizability, hatchability, survival, growth and heterosis. The average fertilization rate of all mating groups was as high as 90.4%, the fertilization rate of the purebred NS (95.2%) being significantly higher than that of the purebred LS or the reciprocal crosses (P < 0.05). The average hatching rate of all genetic groups was as high as 84.7%, the hatching rate of NS (89.4%) being significantly higher than that of the purebred LS or the reciprocal crosses (P < 0.05). The mean survival rate of all crosses from hatching up to the onset of exogenous feeding stood at 94.2%, without showing a significant difference (P > 0.05) between the crosses. During the larval rearing period, which extended from the onset of exogenous feeding up to 15 days of age, NS displayed a significantly lower growth rate (P < 0.001) than that of the purebred LS and their reciprocal hybrids. There was no significant difference (P > 0.05) in survival rate (mean 84.7%) between the four crosses at the end of the larval rearing period. During the juvenile rearing phase, the mean growth performance of all crossbreds was similar to that of the purebred LS and significantly different from that of the purebred NS (P < 0.001). The final individual weights attained by LS, NS, LS × NS and NS × LS were 3.31, 0.71, 3.97 and 3.66 g respectively. The increase in weight attained by the fast-growing crossbred LS × NS was 562.2%, 20.4% and 8.7% more than that of NS, LS and NS × LS respectively. The survival rate of NS (57.1%) was significantly lower (P < 0.001) than that of all the rest of the crosses. The crossbreds displayed about 15.1% heterosis in mean body weight relative to the fast-growing purebred LS. It was concluded that cross-breeding of H. longifilis strains could be advantageous because of the hybrid vigour in the progeny.

Differences in Growth in Blue Catfish Ictalurus furcatus and Channel Catfish Z. punctatus Fed Low‐Protein Diets With and Without Supplemental Methionine and/or Lysine

AbstractThree feeding experiments were conducted to evaluate growth and body composition in blue caffish Ictalurus furcatus or channel caffish I. punctatus when fed diets containing 22% protein with or without supplemented methionine and/or lysine. All experiments were conducted in 110‐L aquaria that were part of a recirculating system. In Experiment 1,15 juvenile blue catfish (2.7 g) were randomly stocked into aquaria and fed one of three diets containing different (22%, 27%, and 32%) percentages of protein. Fish were fed twice daily to excess for 10 wk. In Experiment 2, juvenile blue catfish (5.4 g) were randomly stocked into aquaria and fed one of six diets containing either 22% (diet 1) or 32% (diet 2) protein. The diet containing 22% protein (diet 1) had either 0.3% crystalline L‐methionine (diet 3), 0.4% crystalline L‐lysine (diet 4), or 0.3% L‐methionine + 0.4% L‐lysine (diet 5) added. A sixth diet was formulated to contain 32% protein and 0.2% crystalline L‐methionine. Fish were fed in excess for 12 wk. In Experiment 3, juvenile channel caffish (10.3 g) were stocked and fed diets 14 from Experiment 2, twice daily in excess for 8 wk.In Experiment 1, after 10 wk, final individual weight, weight gain (%), and specific growth rate (SGR) of blue catfish fed diets containing three protein levels were not significantly different (P &gt; 0.05) and averaged 12.9 g, 378%, and 2.2%/d, respectively. Fish fed the diet containing 27% protein had higher (P &lt; 0.05) whole‐body protein (65.4%) compared to fish fed diets containing either 22% or 32% protein. In Experiment 2, final weight, weight gain (%) and SGR of blue catfish were not significantly (P &gt; 0.05) different among diets and averaged 24.7 g, 355%, and 1.8%/d, respectively. Percentage whole‐body protein and lipid were not significantly (P &gt; 0.05) different between fish fed diets containing 22% or 32% protein. In Experiment 3, channel caffish fed a diet containing 32% protein had significantly (P &gt; 0.05) higher final individual weight, weight gain (%), and SGR compared to fish fed diets containing 22% protein, with and without supplemental methionine or lysine.Results indicate that blue catfish may be able to utilize a diet with 22% protein, and that addition of crystalline methionine and/or lysine did not improve growth. However, channel catfish grown in aquaria did not appear to have similar growth when fed a diet containing 22% protein compared to fish fed 32% protein, even when supplemental methionine or lysine was added. Further research on blue catfish and the use of a low‐protein diet (22% protein) needs to be conducted in ponds.

The culture performance of monosex and mixed-sex new-season and overwintered fry in three strains of Nile tilapia ( Oreochromis niloticus) in northern Vietnam

Two experiments (E1, E2) to evaluate the performance of new-season and overwintered fry in three strains (Viet, GIFT and Thai) of Nile tilapia ( Oreochromis niloticus) were conducted at Research Institute for Aquaculture No.1 (RIA-1) in northern Vietnam. The performance of both mixed and monosex fish of the three strains was also compared. The experiments were carried out from May to November (E1) and August to November 1997 (E2) with overwintered and new-season fry, respectively. Each experiment included a comparison of production in fertilized earthen ponds (6×300 m 2) and cages (18×1.2 m 3) suspended within a single pond (1200 m 2). In the pond trials, the three strains were stocked communally as either monosex or mixed-sex groups, whereas treatments (strain×sex) were separated into replicate cages. Individual size of fish stocked was 11.8±0.8 g (E1) and 9.4±0.4 g (E2). Floating pellets were fed at 5% (b.wt. day −1, 30% crude protein) initially, and declined to 2% by the third month of culture. Water quality and fish growth were monitored monthly. Overwintered fingerlings, both mixed and monosex, of all three strains performed well. Daily weight gain (DWG) ranged between 1.8 and 2.3 g day −1 in both ponds and cages. Among the three tilapia strains, the GIFT fish attained a significantly ( P<0.01) larger individual final weight (387.7±21.0 g in ponds; 410.6±35.1 g in cages) compared to the Thai (351.6±26.1 g in ponds; 373.2±30.4 g in cages) and Viet strains (359.5±33.2 g in ponds; 350.3±33.4 g in cages). Overall, monosex fish of the three strains grew significantly faster than mixed-sex fish ( P<0.05). DWG of new-season fingerlings (E2) in ponds ranged from 1.6 to 1.8 g day −1, showing slower growth compared to overwintered fingerlings. There was no significant difference in the growth between the three strains, and between mixed and monosex fish in ponds. Growth of all three strains was significantly slower in cages than ponds (overall DWG=0.8–0.9 g day −1; P<0.01). The results suggest that the performance of overwintered seed compare well with new-season fry. These results are discussed in the context of developing appropriate strategies for tilapia seed productions for northern Vietnam.

Effects of Replacing Fish Meal in Diets on Growth and Body Composition of Palmetto Bass (Morone saxatilis × M. chrysops) Raised in Cages

ABSTRACT Juvenile palmetto bass (Morone saxatilis X M. chrysops) with an average weight of 20 g were stocked into 12 floating cages (1.2 × 1.2 × 2.4 m) and fed one of four practical diets formulated to contain various percentages (0,15, 30, or 45%) offish meal (FM). Diets were formulated to be isonitrogenous (43% protein) and isocaloric (3.9 kcal available energy/g). Fish were fed twice daily, all they would consume in 40 minutes (0900 and 1730), for 125 days. Final individual weight and specific growth rate (SGR) of fish fed diets containing 15, 30, or 45% fish meal were not significantly different (P > 0.05) and averaged 342 g and 2.3%/day, while growth of palmetto bass fed a diet containing soybean meal (SBM), and meat-and-bone meal, without FM, was significantly (P <0.05) lower (282 g and 2.1%/day). There were no significant differences (P >0.05) in percentage moisture, protein, and lipid in fillet from palmetto bass in the four treatments, of which these values averaged 75.1%, 80.7%, and 14.5%, respectively. Amino acid composition of fillets was similar among treatments. These data suggest that a diet containing 15% FM is sufficient for diet palatabiiity and good growth in juvenile palmetto bass. Additional research on diet formulations without FM should be conducted.

Competition Between Triazine-Resistant and -Susceptible Common Waterhemp (Amaranthus rudis)

The relative competitiveness of triazine-resistant (TR) and -susceptible (TS) common waterhemp, as a component of fitness, was assessed using TR and TS biotypes collected from the same field in Fillmore County, Nebraska. Competition between biotypes was evaluated under greenhouse conditions using a set of replacement series experiments with five ratios of TR:TS (1:0, 3:1, 1:1, 1:3, and 0:4) and four plant densities (50, 100, 150, and 300 plants m−2). No difference in final individual plant weight between TR and TS plants was observed in the absence of interbiotypic competition at all plant densities examined. Interbiotypic competition was indicated by ANOVA of plant weight and modified relative crowding coefficients (RCC) for plant weight, height, and volume. Replacement series diagrams showed TS plants were more competitive than TR plants, as measured by plant weight at densities of 50, 100, and 150 plants m−2. TS and TR plants were equally competitive at 300 plants m−2. Individual TS plant weight for 50, 100, and 150 plants m−2was greatest at the 3:1 ratio (TR:TS) and decreased as the proportion of susceptible plants increased. Individual TR plant weight for 50, 100, and 150 plants m−2was greatest at the 1:0 ratio and decreased as the TR proportion decreased. Lack of interbiotypic competition at 300 plants m−2and decreasing TS plant weight with increasing ratios suggest intrabiotypic competition. RCC values for volume and height were calculated weekly during the experiment and indicated the competitive advantage of TS plants was constant from transplanting through harvest.

Ascorbic acid metabolism in fish: is there a maternal effect on the progeny?

High maternal ascorbic acid intakes have been shown to ‘condition’ the ascorbic acid requirement of guinea pig offspring. To examine whether a similar effect exists in fish, and what the relative importance of both maternal and offspring ascorbic acid intake is on offspring performance, rainbow trout offspring from females fed high (360 mg kg −1) or ascorbic acid free (0 mg kg −1) diets were maintained on both a high (500 mg kg −1) or marginal (20 mg kg −1) ascorbic acid diet. A high ascorbic acid status of the egg protected hatched fry against increased mortality due to a marginal ascorbic acid intake. Mortality of high ascorbic acid offspring was not affected by the dietary ascorbic acid level until after 18 weeks of initiation of exogenous feeding. However, the marginal diet did result in a significantly lower individual weight starting at Week 7 (final body weight: 2.5 ± 0.4 g, marginal ascorbic acid and 4.8 ± 0.6 g, high ascorbic acid intake). Ascorbic acid deficient offspring fed a marginal ascorbic acid diet showed continuously high mortalities, reaching 92.3 ± 1.9% after 15 weeks. Feeding the high ascorbic acid diet to the ascorbic acid deficient offspring led to significant growth recoveries. Final individual fish weight was not significantly different between the ascorbic acid deficient or the high ascorbic acid offspring fed a high ascorbic acid diet. Survival of both groups fed a high ascorbic acid diet were identical from Week 7 onwards. However, the initially higher mortality in the low ascorbic acid offspring resulted in a significantly higher (71.1 ± 2.2% vs 59.6 ± 6.4%) cumulative mortality. Experiments with radiolabeled ascorbic acid did not reveal significant differences in ascorbic acid conservation after 3 months of feeding.

Effects of feeding the repartitioning agent L644,969 on growth and body composition of blue catfish, Ictalurus furcatus, fed diets containing two protein levels reared in cages

Juvenile blue catfish with an average initial weight of 110 g, were stocked into 3.5-m 3 floating cages at a rate of 200 fish/cage and fed one of four diets. Diets contained either 27 or 36% protein and either 0 or 3 mg/kg of the beta-adrenergic agonist (BAA) L644,969. There were three replicates per diet. Fish were fed all they would consume in 40 min for 94 days. There was no significant effect of protein, L644,969, or their interaction ( P > 0.05) on final individual weight, percentage weight gain, survival, and specific growth rate (SGR). No difference ( P > 0.05) in whole body composition was found between protein levels; however, fish fed diets containing L644,969 had a higher ( P < 0.05) fillet dressout and a lower ( P < 0.05) percentage of abdominal fat than fish fed control diets. The fish fed 3 mg L644,969/kg diet had 15% more protein and 28% less lipid in the fillet than fish fed control diets ( P < 0.05). Fish fed diets containing L644,969 also had a significantly higher ( P < 0.05) percentage of protein and a lower percentage of lipid in viscera than fish fed diets without the BAA. These results indicate that blue catfish reared to 485 g in cages can be fed as much as they will consume of a diet containing 27% protein without adversely affecting growth, and that the addition of 3 mg L644,969/kg to diet containing either 27 or 36% protein reduces lipid deposition in muscle and visceral depots while increasing protein accretion in muscle.

Comparative growth of reciprocal carp hybrids between Catla catla and Labeo fimbriatus

Intergeneric hybrids between catla ( Catla catla) and fimbriatus ( Labeo fimbriatus) were produced by employing the technique of hypophysation and dry stripping. Detailed investigations on their embryonic and larval development, taxonomic characters and aquaculture potential in terms of growth, feed utilization, body carcass composition, meat yield etc. were carried out. The growth experiment was conducted in concrete tanks (5 × 4 × 1.2 m) in triplicate following normal rearing practice for a period of 154 days. Growth was assessed at 14-day intervals. At the time of fish sampling, water and plankton were also analyzed. It was revealed that the growth of the hybrids was intermediate to the parental species. The final individual weights attained by catla, fimbriatus, catla X fimbriatus (male parent named first) and fimbriatus X catla were 64.2, 24.1, 39.8 and 57.8 g, respectively. Among the hybrids, the growth of fimbriatus X catla was faster than the slow-growing parent fimbriatus and the reciprocal cross hybrid and slightly less than fast-growing catla. The increase in weight attained by fimbriatus X catla was 153.4 and 45.0% more than fimbriatus and the reciprocal hybrid, respectively, but not different from catla. During the course of the investigation it was also observed that the hybrids combined desirable qualities such as the small head of the fimbriatus and the deep body of the catla and exhibited heterosis in terms of meat yield with higher flesh content than either of the parents. Hence the hybrids appear to be of considerable importance to aquaculture.

Growth of control and androgen-treated Nile tilapia, Oreochromis niloticus (L.), during treatment, nursery and grow-out phases in tropical fish ponds

. Masculinization of sexually undifferentiated tilapia fry is achieved by oral administration of the androgen 17-α methyltestosterone (MT). An anabolic response to androgen treatment of tilapia has been reported. Growth of control and MT-treated tilapia was evaluated during consecutive treatment, nursery, and grow-out phases under conditions approximating commercial, semi-intensive tilapia farms in Central America. Oreochromis niloticus (L.) fry were fed a 0 or 60 mg/kg MT diet for 28 days. Growth curves for control and MT-treated fish did not have significantly different slopes. Mean harvest fry weights were similar, averaging 0·1 g/fry for both treatments. Fry were subsequently stocked into 0·2-ha nursery ponds for 94 days growth. Slopes of control and MT-treated fish growth curves were not significantly different. Mean final individual weights did not differ significantly between treatments. Control fish did not deviate significantly from the1:1 male: female ratio, but MT-treated fish were 97% males. Control male and MT-treated male fingerlings were stocked for grow-out into 0·1-ha organically fertilized earthen ponds. No significant difference in growth was observed between control and MT-treated fish. Mean gross yields after 150 days and mean final individual weights were similar for both treatments.