Fish Mean Weight Research Articles

Cage culture of sutchi catfish, Pangasius sutchi (Fowler 1937): effects of stocking density on growth, survival, yield and farm profitability

The sutchi catfish, Pangasius sutchi (Fowler 1937) was grown at 10 stocking densities in cages suspended in a river-fed channel during the summer of 2000. Catfish fingerlings (mean length 9.1–9.7 cm and mean weight 5.9–6.7 g) were stocked at densities of 60, 70, 80, 90, 100, 110, 120, 130, 140 and 150 fish m−3. After 150 days, growth and yield parameters were studied and a simple economic analysis was carried out to calculate profitability. The mean gross yield ranged from 15.6±0.27 to 34.5±0.44 kg m−3 and the net yield ranged from 15.2±0.22 to 33.5±0.36 kg m−3 and showed significant variations (P<0.05). The mean weights of fish at harvest were inversely related to stocking density. Both gross and net yields were significantly different and were directly influenced by stocking density but the specific growth rate, survival rate and feed conversion rate were unaffected. Higher stocking density resulted in higher yield per unit of production cost and lower cost per unit of yield. The net revenue increased positively with increasing stocking density. A density of 150 fish m−3 produced the best production and farm economics among the densities tested in this experiment.

Winter ulcer disease of post-smolt Atlantic salmon: An unsuitable case for treatment?

The plasma concentrations of florfenicol (FF) were measured during a 10-day oral administration of this agent to fish in a cage in a commercial salmon farm. The therapy was initiated as part of a management response to an outbreak of winter ulcer disease associated with a Moritella viscosa infection. Twenty healthy, 20 moribund and 10 dead fish were sampled 24 h after the administration of medicated feed on the eighth day of the therapy. Quantifiable concentrations of FF were detected in all 20 healthy fish with a mean plasma concentration of 3.0 ± 1.8 mg/ml. These data are consistent with previously published data and with parallel laboratory trials performed in this work. The mean weight of these healthy fish was 324 ± 89 g but M. viscosa was isolated from only one of them. With respect to the moribund fish, FF could not be detected in 18 of the 20 fish analysed and the mean weight of these fish was 196 ± 48 g. M. viscosa was isolated from 19 of the 20 moribund fish. The mean MIC value for FF against 14 of the M. viscosa isolated was 0.24 mg/l and it is argued that, in the context of this therapy, these bacteria should probably be classified as sensitive to FF. The analysis of the patterns of mortality before, during and after the period of therapy did not provide any unambiguous evidence that the therapy was, however, effective in reducing death in the cage population. The data generated in this work and in a previous study of winter ulcer disease is used to develop a tentative model of the epizootiology of this disease in post-smolts. In both studies there was a strong correlation between the weights of fish and their health. This suggests that, within a cage population, infection by M. viscosa, ulceration and death are largely confined to a sub-population that has adapted poorly to the environment of the marine cage. Further, as this poorly adapted sub-population is not feeding, it is unlikely that orally administered antimicrobial therapy would represent a cost-effective way of limiting losses.

An Economic Comparison of Producing Catfish, Ictalurus punctatusStockers with Either 9-cm, 11-cm, or 13-cm Fingerlings

A pond production study was conducted to analyze the effect of fingerling size at stocking on net yield, growth, final size, and feed conversion ratio of stocker catfish produced on farm. Channel catfish, Ictalurus punctatusfingerlings of either 9-cm, 11-cm, or 13-cm were stocked into 0.04-ha earthen ponds at 100,000/ha for 116 days. Stocking larger fingerlings significantly (P < 0.05) increased total yield, net yield, net daily yield, growth, final weight, final length, and FCR. Total yield was related linearly to size of fingerling at stocking (y = 732.3x – 3513.5; R2 = 0.93). Mean weight of fish at harvest was related linearly to the size of fingerling at stocking (y = 10.841x – 41.159; R2 = 0.83). Total operating costs ($/ha) and breakeven costs per stocker ($/fish) increased with increasing size of fingerling stocked while breakeven price on a weight basis ($/kg) decreased with increasing size of fingerling stocked. The risk of production costs exceeding market price was lower for production of larger stockers, but the greater capital requirements associated with the higher yields of larger stockers may increase financial risk farm wide.

Nutrient release and resuspension generated by ruffe (Gymnocephalus cernuus) and chironomids

Summary1. Benthivorous fish may play an important role in internal nutrient loading. Ruffe are highly specialised, feeding exclusively on bottom animals; thus all nutrients released via their feeding are derived from the bottom and are new to the water column. The fish can also release nutrients from the sediment through resuspension while searching for food.2. The aim of this study was to estimate experimentally in the laboratory the effect on water quality of resuspension and nutrient release by ruffe and bottom animals (chironomids).3. Ruffe released nutrients during 8 h experiments as follows: total P 1.4, dissolved PO4 0.6, total N 24.0 and NH4‐N 15.9 μg g−1 WW h−1. A decreasing trend in mass‐specific release was observed over time, probably because of starvation. The mass‐specific release of total N and NH4‐N decreased as the mean weight of fish increased. The mean ratio of excreted N : P was 32.4. In 26 h experiments with sediment and both ruffe and chironomids, ruffe increased nutrient concentrations and turbidity values significantly but chironomids had an effect only on turbidity. Neither ruffe nor chironomids affected the ratio of inorganic N : P concentrations. An interaction between ruffe and chironomids was found for turbidity.5. According to these results, benthivorous fish may increase nutrient concentrations in the water column and need to be taken into account when estimating internal loading.

Deep-water fish assemblages in the Mediterranean Sea

Data collected during the DESEAS survey carried out in three areas of the Mediterranean Sea (Balearic Sea, western and eastern Ionian Sea) were used to describe the structure and spatial distribution of the fish assemblages at depths between 600 and 4000 m. A total of 55 species (8 chondrichthyes and 47 teleost fish) were sampled, 38 of them in the Balearic Sea, 30 in the western Ionian and 37 in the eastern Ionian. Multivariate analysis showed a clear pattern of zonation with depth and geographic area. Three main assemblages were identified across the vertical gradient investigated: on the upper slope around a depth of 600 m, on the middle slope between 800 and 1300 m, and on the lower slope below 1300 m. The geographic characterisation of the ichthyofauna structure was mainly observed on the upper and middle slope. The highest abundance and biomass values were found at depths of 1000-1200 m due to the presence of larger species with high energy requirements, such as Alepocephalusrostratus, Mora moro and Galeus melastomus. On the middle slope, significant differences in the abundance, biomass and mean fish weight were detected between the three areas. Significant differences for these parameters were also shown between the middle and lower slope assemblages. A significant decrease in species richness and diversity was shown with increasing depth, indicating an impoverishment of the megafauna with depth and a higher similarity between the Balearic Sea and the Ionian Sea with regard to the greatest depths. The dominant species on the deepest bottoms were Bathypteroismediterraneus, Chalinura mediterranea and Coryphaenoides guentheri. On the lower slope, the shark Centroscymnuscoelolepis was also found to be relatively abundant off the Balearic Islands, Etmopterusspinax in the eastern Ionian Sea and the teleost fish Cataetyx laticeps throughout the three study areas. The deepest bottoms of the Mediterranean Sea shelter an ichthyofauna dominated by small-medium species living in a food scarce environment in which some large mobile fishes are widespread. The results are discussed in relation to previous studies mostly carried out in the Atlantic and western Mediterranean.

Effect of dietary carbohydrate-to-lipid ratios on growth, lipid deposition and metabolic hepatic enzymes in juvenile Senegalese sole (Solea senegalensis, Kaup)

A study was undertaken to determine the effect of various dietary carbohydrate-to-lipid ratios on growth performance, whole-body composition and tissue lipid content in Senegalese sole (Solea senegalensis) juveniles. Data on the dietary regulation of key hepatic enzymes of the lipogenic and glycolytic pathways (glucose-6-phosphate dehydrogenase, G6PD; malic enzyme, ME; fatty acid synthetase, FAS; pyruvate kinase, PK and glucokinase, GK) were also generated. Four isonitrogenous (crude protein: 52% dry matter (DM)) diets were formulated to contain one of two lipid levels (11% and 21% DM). Within each dietary lipid level, the nature of the carbohydrate fraction (raw or extruded peas) was varied. Triplicate groups of 54 sole (initial body weight: 23.6±1.2 g) were grown in recirculated seawater over 67 days. Fish were fed using automated feeders. At the end of the study, whole-body, liver, viscera and muscle samples were withdrawn for analyses. During the experimental period, the mean fish weight about doubled in all treatments. No significant differences were found in growth performance (ranging from 1.1% to 1.4% body weight day−1) among dietary treatments. High-fat diets increased whole-body fat content. Similarly, daily fat gain ranged from 0.54 to 0.78 g kg−1 day−1 and highest values were found in fish fed high-lipid diets. Dietary treatments also affected tissue lipid content (liver, viscera and muscle), with highest values in fish fed high-fat diets. The nature of dietary carbohydrates had little influence on performance criteria, but affected tissue lipid deposition. The activities of G6PD, ME and FAS were depressed by elevated levels of dietary lipid, confirming the inhibitory effect of dietary fats on lipid biosynthesis. At both dietary lipid levels, ME and FAS activities were little affected by dietary carbohydrate. Activities of PK and GK were not affected by the starch level of the diets. In Senegalese sole juveniles, the lipogenic pathway is more susceptible to modulation by dietary means (particularly through lipid intake) than the glycolytic pathway.

Efficacy of Streptococcus agalactiae (group B) vaccine in tilapia ( Oreochromis niloticus) by intraperitoneal and bath immersion administration

We evaluated the effectiveness of a Streptococcus agalactiae vaccine in tilapia ( Oreochromis niloticus) for prevention of streptococcal disease. The vaccine was prepared from formalin-killed cells and concentrated extracellular products (greater than 3 kDa) of a single isolate of S. agalactiae (ARS-KU-MU-11B). Intraperitoneal (IP) and bath immersion (BI) vaccine trials were conducted at two temperatures, 32 and 26 °C, and mean fish weights, 5 and 30 g. Control tilapia were injected with tryptic soy broth. Thirty gram tilapia vaccinated and challenged by IP injection with 1.5×10 4 colony-forming units (CFU)/fish of Streptococcus agalactiae at 30 days post-immunization had a relative percent survival (RPS) of 80. Smaller tilapia vaccinated and challenged under similar conditions had an RPS of 25. An RPS of zero was noted in 30 g fish IP vaccinated with Streptococcus iniae and IP challenged with S. agalactiae. The 5 and 30 g tilapia bath immunized with S. agalactiae and IP challenged with 3.6×10 5 and 1.7×10 6 CFU/fish of S. agalactiae had RPS values of 34. Intraperitoneal administration of the vaccine provided efficacious protection only in the 30 g tilapia regardless of whether the fish were immunized and challenged at 26 or 32 °C. Bath immunization of both 5 and 30 g tilapia resulted in RPS values that were two times lower than those achieved with IP vaccination. The results of this study suggest that there is a lack of cross-protection of S. iniae bacterins against S. agalactiae challenge. Protection against S. agalactiae infection is, however, provided through vaccination with a S. agalactiae modified bacterin vaccine.

Effect of periphyton on growth performance of grey mullet, Mugil cephalus (Linn.), in inland saline groundwater ponds

Summary The present study attempts to assess the potential of artificial substrates to enhance fish production in inland saline groundwater ponds through periphyton production. Grey mullet, Mugil cephalus, was cultured for 100 days in ponds with substrate (treatment ponds) and without substrate (control ponds). To enhance the surface area, bamboo poles were used as substrate. The periphyton population, pigment concentration and hydrobiological characteristics of pond water were monitored. The studies revealed little difference in most of the water quality parameters observed in the two treatments. However, turbidity (27.0 ± 0.1–35.0 ± 0.1 Nephalo Turbidity Unit (NTU)), chlorophyll ‘a’ (6.6 ± 0.6–7.6 ± 0.6 μg L−1), plankton population (phytoplankton 8.4 × 103–9.4 ×103 numbers L−1; zooplankton 4.0 × 103–5.1 × 103 numbers L−1) and NH4–N (2.0 ± 0.2–2.3 ± 0.1 mg L−1) were high in the treatment with no additional substrate; however, in the treatment with substrate the total Kjeldahl nitrogen (9.8 ± 0.8–10.8 ± 0.7 mg L−1) and o-PO4 (0.1 ± 0.01–0.1 mg L−1) remained significantly (P < 0.05) higher. Highest periphyton biomass in terms of dry matter (DM) (0.8 ± 0.01–1.4 ±0.01 mg cm−2), ash free DM (0.4 ± 0.0–0.6 ± 0.01 mg cm−2), chlorophyll ‘a’ (3.1 ± 0.2–8.1 ± 0.8 μg cm−2) and pheophytin ‘a’ (1.9 ± 0.4–3.9 ± 0.5 μg cm−2) was observed at 50 cm depth in ponds provided with additional substrate. Fifteen plankton genera showing periphytic affinity colonized the bamboo substrates. Fish growth (mean fish weight 524.3 ± 8.7 g and SGR 2.5 ± 0.1) was significantly (P < 0.05) higher in ponds provided with additional substrate compared with control ponds (387.2 ± 6.0). Length–weight relationship (LWR) (W = cLn) also showed that the exponential value (‘n’) of length was high in substrate-supported ponds (n = 2.36) in comparison with controls (n = 1.09). These studies suggest that a periphyton-supported aquaculture system can be used successfully for the culture of herbivorous brackishwater fish species like M. cephalus in inland saline groundwaters and thus could contribute to the development of sound and sustainable aquaculture technology.

High-rate algal pond treatment for water reuse in an integrated marine fish recirculating system: effect on water quality and sea bass growth

A high-rate algae pond (HRAP) was tested as a second loop of water treatment in a recirculating fish rearing system to reduce water requirements and nutrient discharge levels. Three duplicated groups of sea bass (mean initial body weight 35±11 g) were reared under different system conditions (flow-through system, recirculating system and recirculating system with HRAP) for 1 year. Fish survival rate was higher in the system with HRAP, and their mean body weight was statistically higher ( p<0.05) during the month of maximal climatic conditions for algae photosynthesis. After 266 days of experiment, mean fish weight was significantly higher ( p<0.05) in the flow-through system than in the recirculating systems. Final fish weight was 15% higher in the flow-through system than in recirculating systems and was related to a higher daily-ingested food. The comparison of mean annual nutrient concentrations in the recirculating systems gives a statistically significant reduction of 25% of nitrogen ( p<0.01) and 9% of phosphates ( p<0.01) due to the HRAP. Absorption of nitrate form is responsible for nitrogen removal and is related to climatic conditions for algae growth. The phosphate precipitation at high pH (above 8) was not considered. The maximal removal rates were 0.5±0.2 g N m −2 day −1 and 0.03±0.02 g P m −2 day −1 for nitrates and phosphates, respectively, and were obtained during the optimal climatic conditions and the shortest algae harvesting frequency. These results are favourable to complete reuse of the HRAP treated water, all year long, in the recirculating rearing systems. In order to improve nitrate and phosphate removal rates, a periodic harvesting of algae is necessary and a higher water inflow in HRAP should partly make up for inorganic carbon depletion in high nitrate and phosphate effluents.

Growth testing of two breeds of common carp, Cyprinus carpio L. (Hungarian mirror and Třeboň scaly carp), in ponds with low and high stocking density

The growth of two breeds of common carp, Cyprinus carpio L., was tested in ponds under the climatic conditions of South Bohemia. Třeboň scaly carp (TR) and Hungarian mirror carp (M2) were kept in both low and high stocking densities during the second growing season and then stocked together for communal testing during the third growing season. Before the communal testing, the mean initial weights of fish from low- and high-density stocks differed significantly (374.1 vs. 227.7 g for the TR breed and 766.7 vs. 317.3 g for the M2 breed respectively, P<0.01). After communal testing, mean weights of fish from low- and high-density stocks gained 761.8 vs. 543.8 g for the TR breed and 1339.7 vs. 706.7 g for the M2 breed respectively. These observed weights were also significantly different (P<0.01). However, the test of corrected weight gain, i.e. gain not related to the initial weight of fish, revealed insignificant differences (P>0.01) between the weight gains after correction, i.e. the effect of different initial weights was successfully eliminated. These results seem to confirm the applicability of this method for the assessment of growth of purebred common carp under the climatic conditions of Central European fish farms.

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.

Development and Laboratory Evaluation of a Bioenergetics Model for Subadult and Adult Smallmouth Bass

A previously developed bioenergetics model for smallmouth bass Micropterus dolomieu (Hewett and Johnson 1992) was originally constructed with data exclusively from age-0 fish but has since been used to predict growth and food consumption for both age-0 and older fish, including adults. We developed a bioenergetics model for subadult and adult smallmouth bass and compared the abilities of the two models to predict growth and food consumption for fish weighing from 100 to 270 g. Model-independent laboratory growth and food consumption data for individual subadult and adult fish were used to evaluate the performance of both models. Experimental fish were subjected to three consecutive 3-week feeding regimes: an ad libitum ration at 22°C, a ration of 2.5% wet body weight/d at 22°C, and a ration of 2% wet body weight/d at 27°C. Overall, the bioenergetics model developed for subadult/adult smallmouth bass produced significantly greater accuracy in estimates of relative growth rate and cumulative consumption for subadult and adult fish than did the age-0 model. The subadult−adult model tracked observed changes in mean fish weight more closely than did the model developed for age-0 fish, and the mean percentage errors in predicting cumulative consumption were consistently lower for the subadult−adult model. Our findings are consistent with previous studies, which have also found that bioenergetics models developed for a particular life stage of a species can yield substantially inaccurate predictions of growth and consumption for other life stages of that species. The model developed for subadult and adult fish produced better agreement with observed growth and food consumption by subadult and adult smallmouth bass than the model developed for age-0 fish and is recommended for applications involving fish weighing more than 50 g.

Oilcakes as protein sources in supplementary diets for the growth of Cirrhinus mrigala (Ham.) fingerlings: laboratory and field studies.

Five isonitrogenous diets (1-5) with 40% protein using oilcakes as protein sources were formulated and fed to Cirrhinus mrigala fingerlings maintained both under laboratory and field conditions. Water soaking of oilcakes for 24 h before incorporation in the diets helped in the reduction of antinutrient factors (phytase and tannins). Live weight gain in fish fingerlings fed on a diet containing groundnut oilcake (GNOC) was significantly (P < 0.05) enhanced in comparison to the other dietary treatments when examined at the end of a feeding schedule. Laboratory studies have further revealed that APD, PER, GPR and GER values were significantly (P < 0.05) enhanced, while those of feed conversion ratio were significantly (P < 0.05) reduced in fish fed on diet 1 containing GNOC. An analysis of water samples collected at two hourly interval from the aquaria revealed low levels of total ammonia (N-NH4+) excretion and reactive phosphate (O-PO4) production in fish fed on diet 1. Proximate carcass composition also revealed high accumulation of protein, fat, energy and phosphorus in fingerlings fed on a diet containing GNOC. Even in field studies a significant (P < 0.05) increase in mean fish weight gain and specific growth rate (SGR% d(-1)) was observed in fingerlings fed on diet 1, followed by canola (2), sunflower (3), mustard oilcake (4) and sesame (5). Water and sediment quality characteristics also correlated well with fish growth.

Initial Mortality of Black Bass in B.A.S.S. Fishing Tournaments

We studied the initial mortality of black bass Micropterus spp. that were captured, weighed in, and released in fishing tournaments conducted by the Bass Anglers Sportsman Society between 1972 and 1998. Mean annual initial mortality (i.e., mortality before weigh-in and release) ranged from 1% to 30%. Initial mortality was greatest during the 1970s (15.2%) and decreased during the 1980s (5.7%) and 1990s (1.9%). Because initial mortality was uniformly low (≤5%) after 1982, we used results for 1983–1998 to assess relationships involving initial mortality. Initial mortality was correlated with bag size, mean fish weight per angler, and number of fish per angler. Logistic regression showed that these three variables and their interactions explained significant portions of the variation in black bass initial mortality. Our results suggest that the initial survival of black bass caught in tournaments can be improved by reducing the number or total weight of fish that anglers can hold in their live wells during the day. This could be accomplished by decreasing tournament bag limits.

Evaluation of raw and hydrothermically processed leguminous seeds as supplementary feed for the growth of two Indian major carp species

To study the effect of four different raw and hydrothermically processed leguminous seeds, namely Glycine max (soybean), Vigna radiata (moong), Vigna ungiculata (cowpea) and Cyamopsis tetragonaloba (guar) on growth in the fingerlings of Cirrhinus mrigala (mrigal) and Labeo rohita (rohu), two experiments were conducted. The first experiment was conducted under laboratory conditions (LD 12:12 at 25 °C) and the mrigal fingerlings were fed @2% BW d−1 for 30 days. Before using the seeds as feeds, they were hydrothermically processed (15 lbs at 121 °C for 15 min) for the elimination of antinutrient factors (ANF). The results indicate that 15 minute autoclaving significantly reduces the trypsin inhibitor activity. Phytase-phosphorous and tannins were also analysed from raw and treated beans. Studies on mrigal have revealed that weight gain was significantly low (P < 0.05) in the fish fed on raw beans compared with the fingerlings fed on processed bean proteins. Among the various raw diets used, significantly highest growth (P < 0.05) was observed in fish fingerlings fed on raw moong, followed by raw soybean, cowpea and guar. On the other hand, when beans were processed, the highest growth was observed in fingerlings fed on processed soybean. Studies have further revealed that hydrothermal processing also affected the values of the feed conversion ratio, gross conversion efficiency, protein efficiency ratio, gross protein retention, gross energy retention and ammonia excretion. Proximate composition of the carcass revealed high accumulation of protein, fat and energy in fingerlings fed on processed soybean in comparison with other diets. Keeping in view the higher weight gain in fish fed on hydrothermically processed bean proteins, only processed bean diets were fed to the fingerlings of mrigal and rohu stocked in fish ponds (experiment 2). A significant (P < 0.05) increase in mean fish weight, and specific growth rate was observed in fingerlings fed on hydrothermically processed soybean, followed by moong and cowpea. Weight gain for mrigal fingerlings remained significantly low in comparison to the rohu fingerlings fed on similar diets. An investigation on the effects of feeds on water quality parameters indicate that the trophic status of the ponds where soybean was used as fish feed remained high in comparison to the other treatments. A significant positive correlation of nutrients, NPP and plankton population with fish growth was also observed.

The Effect of Rearing Density on Growth, Survival, and Feed Conversion of Juvenile Atlantic Sturgeon

Abstract We investigated the effect of rearing density on the growth and survival of juvenile Atlantic sturgeon Acipenser oxyrinchus using initial rearing densities ranging from 10 to 30 fish per tank or 3.6–10.9 kg/m2 of substrate. The mean weight of fish at the start of the trial was 368.7 g. After 7 weeks of rearing, density ranged from 6.5 to 16.3 kg/m2 (14.7–36.6 g/L). Fish reared at the lowest density had significantly higher mean weight and length at the end of the trial. Growth over the 7-week experiment was modeled as a function of time, and growth rate was inversely proportional to density. The mean increase in total biomass was 63.14%, and the mean daily length gain was 0.23%. Overall survival was 99.7%, and calculated feed conversion rates ranged from 1.93 to 2.65. However, feed conversion rates were likely not at maximum levels due to the selection of a relatively high experimental feeding rate (2.5% of body weight per day).

Effects of Reduced Levels of Dietary Protein and Menhaden Fish Meal on Production, Dressout, and Biochemical Composition of Phase III Sunshine Bass Morone chrysops ♀× M. saxatilis ♂ Cultured in Earthen Ponds1

AbstractThe responses of phase III sunshine bass Morone chrysops ♀× M. saxatilis ♂ to diets containing reduced levels of menhaden fish meal (30–10%, dry weight) and crude protein (40–36%, dry weight) were evaluated in two separate experiments. Reductions in fish meal were compensated by increase in dietary soybean meal, a meat and blood meal product, and additional amounts of a 1:1 catfish oil:menhaden oil mixture sprayed on as a top dressing. Fish were cultured in earthen ponds and fed commercially manufactured, extruded diets to apparent satiation. In Experiment 1, dietary crude protein was reduced from 40 to 36% and the menhaden fish meal ingredient was reduced from 30 to 15% (dry weight). The mean weight of fish stocked into each pond ranged from 144 to 188 g, the stocking density was 8641/ha, and the duration of the growout was 172 d. In Experiment 2, both dietary treatments contained 40% crude protein (dry weight) and either 30% or 10% menhaden fish meal. The mean weight of fish stocked into each pond ranged from 42 and 77 g, the stocking density was 8,500/ha, and the duration of the growout was 175 d. Simultaneous reductions in dietary menhaden fish meal and crude protein resulted in significant decreases in all production indices except survival and percent weight increase. Weights of filet, carcass, liver and intraperitoneal fat, expressed as a percent of total body weight, were not significantly different. A 66% reduction in dietary menhaden fish meal while the crude protein level was maintained at 40% did not significantly affect growth, production, and weights of filet, carcass, liver and intraperitoneal fat, expressed as a percent of total body weight, and represents a 6% decrease in the cost of feed. In both experiments, levels of protein, lipid, moisture, and ash of the whole body and the filet were not significantly different. Fatty acid composition of the filet and livers from fish fed the control and experimental diets in Experiment 2 were highly comparable. The comparable level of performance of fish fed diets believed to be deficient in HUFA suggests that the dietary levels reported to be required may not be totally applicable to diets formulated for pond culture.

The effect of whole body lipid on early sexual maturation of 1+ age male chinook salmon ( Oncorhynchus tshawytscha)

Early sexual maturation of male chinook salmon (maturation 1 to 4 years prior to females in the same age class) results in reduced effectiveness of stock enhancement programs and a financial loss to the salmon farming industry. Previous studies in Atlantic salmon have shown that the age of maturity in males is affected by growth and/or body energy stores, but the relative roles of these two factors are not well understood. Therefore, an experiment was designed to determine when spermatogenesis was initiated, to characterize the endocrine changes during the onset of puberty in male salmon, and to determine if the level of whole-body lipid affects the incidence of early male maturation in a wild stock (Yakima River) of 1+ spring chinook salmon. Fry were fed a commercial diet from February until August and were then divided into groups of 320 fish (mean weight, 5.6 g) and fed one of five experimental diets (two replicate groups/diet) containing 4%, 9%, 14%, 18% or 22% lipid and 82%, 77%, 73%, 69%, or 65% protein for 13 months. Fish were reared on natural photoperiod and ambient temperature (6°C to 16°C), and pair-fed to a level based on the tank with the lowest feed consumption. Fish were weighed monthly and sampled to determine body composition, pituitary follicle-stimulating hormone (FSH) and luteinizing hormone (LH) levels, plasma insulin-like growth factor I (IGF-I) levels, and stage of gonadal development. Throughout the experimental period the mean fish weight was similar among treatment groups. However, from December through the end of the experiment in the following September, maturing males were significantly larger than nonmaturing fish. Initial lipid levels in 0-age experimental fish were near 6%, which is similar to wild fish of the same stock and age captured in the Yakima River during August. Fish fed diets containing more than 4% lipid increased in whole-body lipid content during the first 2 months of feeding and then maintained at relatively constant levels during the course of the experiment. Whole-body lipid levels for the dietary treatment groups averaged 5.6%, 7.1%, 8.2%, 9.4%, and 9.6% from October through the following September. Based on histological examination of the testes of experimental fish, type B spermatogonia and primary spermatocytes were first observed in some of the yearling males during November. These were designated maturing males. Pituitary FSH levels were significantly higher in maturing than nonmaturing males at this time and for the remainder of the study. Pituitary FSH levels increased as spermatogenesis proceeded in maturing fish, whereas pituitary LH levels increased in maturing 1+ males only during July and August, when testes were in late stages of spermatogenesis and in September during spermiation. Plasma IGF-I levels were significantly higher in maturing males than nonmaturing fish from December through the end of experiment. Since maturing males were significantly larger than nonmaturing fish of both sexes from December through September, the difference in IGF-I levels could be due to differences in growth or due to maturation. The percentage of maturing males was significantly influenced by whole-body lipid, increasing from 34% in fish fed the 4% lipid diet to 45% in fish fed the 22% lipid diet. These data suggest that whole-body lipid levels influenced the incidence of maturation of male spring chinook salmon. In addition, both endocrine and histological indicators suggest that maturation was initiated in males approximately a full year prior to the time the fish will spawn.

Influence of dietary fat and adiposity on feed intake of juvenile red sea bream Pagrus major

A two-phase experiment was conducted to examine the effects of dietary fat and adiposity on feed intake of red sea bream. In Phase 1, juveniles (9.7 g, 20 fish tank −1, 4 replicates) were fed low fat (LF; 15.3% fat, 60.6% protein, 22.2 kJ g −1 energy, 0.61 g ml −1 density) or high fat (HF; 24.6% fat, 54.9% protein, 24.2 kJ g −1 energy, 0.68 g ml −1 density) diets for 4 weeks to produce fish which differed in adiposity. In Phase 2, all groups were fed the LF and HF diets alternately for 8 days. Fish were fed to apparent satiation by hand twice daily and daily feed consumption was recorded. Fish were weighed at the start, weekly during Phase 1 and at the end of Phase 2. Proximate composition was determined at the start of the experiment and after Phase 1 and 2. In Phase 1 the amount (18.6±0.35 vs. 17.1±0.19 g) and volume (30.6±0.58 vs. 25.2±0.28 ml) of feed consumed was significantly greater in fish fed the LF diet; energy intakes (LF, 412±7.8; HF, 413±4.7 kJ) and terminal mean fish weights (LF, 28.2±0.5; HF, 27.7±0.1 g) were similar. Fish fed the HF diet had a significantly higher proportion of visceral (37.6±1.5 vs. 28.9±1.2%) and carcass fat (9.7±0.3 vs. 8.0±0.3%). In Phase 2, fish fed the LF diet in Phase 1 consumed more of both the LF diet (2.9±0.2 vs. 2.4±0.1 g, P<0.05) and HF diet (3.2±0.1 vs. 2.9±0.1 g, P<0.07). Within each treatment fish consumed equal volumes of HF and LF feed, but the fish fed the LF diet in Phase 1 consumed a significantly greater total volume of feed (9.5±0.4 vs. 8.1±0.3 ml). Fish weights at the end of Phase 2 did not differ (LF, 34.6±0.9 vs. HF, 33.8±0.4). Our results indicate that the fish ate to meet an energy demand during Phase 1 and suggest that stomach volume increased in fish fed the lower energy (LF) diet, allowing increased meal size. This increase in meal size persisted when these fish were fed alternating HF or LF diets for 8 days (Phase 2). We were unable to unequivocally demonstrate an effect of adiposity on appetite during Phase 2, although this can be inferred since the fish fed the HF diet in Phase 1 should also have had the ability to increase their feed intake during Phase 1, but did not.

Effects of acute exposure to fluoranthene-contaminated sediment on the survival and genetic variability of fathead minnows (Pimephales promelas)

One-month-old fathead minnows (Pimephales promelas) were exposed to fluoranthene-contaminated sediment (1.24 mg/gm organic carbon) during a 96-h exposure. Of the 909 minnows exposed to fluoranthene, 684 (75%) minnows died during the exposure. Horizontal starch-gel electrophoresis was used to determine genotypes at six variable enzyme loci (β-GAL*, GPI-1*, GPI-2*, IDHP-1*, MDH-2*, and PGM*). Statistical analyses were used to evaluate the relationships between the genetic data and weight, length, and time to death (TTD) offish using an accelerated failure time regression model (LIFEREG). The GPI-1*, MDH-2*, and PGM* loci were found to be significantly related to TTD. Multilocus heterozygosity was also related to TTD. Lower heterozygosity was related to a longer TTD and a greater chance of survival. Fish weight was strongly related to TTD and survival. Larger fish had a longer TTD and a greater chance of survival. Mean fish weight differed significantly among genotypes at each locus. This resulted in large differences between LIFEREG regression models that factored weight out and those models that did not separate weight from the genotypes or multilocus heterozygosity. The results of the study indicated that differential survival to fluoranthene was genetically related. The frequencies of several genotypes were significantly different in the survivors of the fluoranthene exposure compared with those in the initial population.