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1.
Rainbow trout ( Oncorhynchus mykiss) maintained in crowded (100 kg m − 3) and uncrowded (20 kg m − 3) conditions were fed 42 days with five experimental diets having different levels of vitamin E (25.6 and 275.6 mg kg diet − 1), C (0 and 1000 mg kg diet − 1) and HUFA (highly unsaturated fatty acids, 12.5 and 320.5 g kg diet − 1): −E−HUFA, −E+HUFA, +E−HUFA, +E+HUFA, −C+E+HUFA. Cortisol, plasma metabolites, tissue glycogen, fish composition, and tissue fatty-acid profile were evaluated at the end of the experimental period. In general, no changes in cortisol levels were associated with crowding, although +E+HUFA and −C+E+HUFA fish showed higher levels (mean ± SE, 55.5 ± 11.1 and 78.0 ± 11.3 ng ml − 1) as a consequence of a possible interaction between chronic crowding and diet composition. Protein and glucose con-centration in plasma displayed no effect of crowding, but liver glycogen showed a general tendency to decrease in −E−HUFA, −E+HUFA, +E−HUFA, +E+HUFA, −C+E+HUFA crowded groups (70.2 ± 2.1, 52.1 ± 2.5, 73.4 ± 7.4, 91.7 ± 3.3, 74.2 ± 8.4 mg g − 1 tissue, respectively) compared to uncrowded groups (108.9 ± 14.2, 82.7 ± 8.8, 92.4 ± 10.7, 99.1 ± 10.0, 103.5 ± 15.6 mg g − 1 tissue, respectively), thus proving significant in −E+HUFA fish. Variations in total lipids, triglycerides, total cholesterol and HDL as well as LDL cholesterol in plasma were manifested under crowding conditions, displaying a certain influence of vitamin E and HUFA dietary content. Final body composition, in general, showed no change attributable to fish density, but some differences associated with diet composition were found in lipid and moisture percentages of crowded fish. Liver and muscle fatty-acid profile revealed a clear effect of the dietary lipid source that was more evident in muscle than in liver at normal fish density, and in some cases this effect was modulated by dietary vitamin E and C content and fish-culture conditions. 相似文献
2.
To examine the age, growth and reproduction of silky sharks, Carcharhinus falciformis, in the waters off northeastern Taiwan, 469 specimens (213 females and 256 males) were collected from August 2000 to January 2002 at the Nanfanao fish market, northeastern Taiwan. The relationship between body weight ( W) and total length (TL) for both sexes combined was expressed as: W = 2.92 × 10 −6 TL 3.15 ( n = 469, p < 0.01). The relationship between TL and vertebral centrum radius ( R) for both sexes combined data was estimated as: TL = 25.979 + 18.197 R ( n = 250, p < 0.01). Growth bands (including translucent and opaque zones) in precaudal vertebrae formed once a year between December and January and were counted up to 11 and 14 for females and males, respectively. The von Bertalanffy growth function (VBGF) was used to model the observed length at age data. The sexes combined VBGF predicted an asymptotic length ( L∞) = 332.0 cm TL, growth coefficient ( k) = 0.0838 year −1, age at zero length ( t0) = −2.761 year ( n = 250, p < 0.01). Size at 50% maturity for males was estimated to be 212.5 cm based on the logistic curve, which corresponded to 9.3 years. Females matured at 210–220 cm, which correspond to 9.2–10.2 years. The length at birth was estimated to be 63.5–75.5 cm TL. The number of embryos per litter was 8–10 and sex ratio of embryos was 1:1. 相似文献
3.
The haddock ( Melanogrammus aeglefinus) is believed to be a potential candidate for aquaculture in the Atlantic coastal countries including the UK, Norway and Canada. However, under culture conditions, haddock will sexually mature prior to the attainment of a suitable harvest weight. Therefore, a long term tank based experiment was performed where three populations of haddock (hatched spring 2002, approximately 150 fish per population) were exposed to either a simulated natural photoperiod (SNP) or SNP until January or July 2003 and thereafter continuous illumination (Jan LL or July LL respectively) with individual growth rate and maturation status being recorded until July 2004 (27 months post-hatch). While the SNP treated population matured in the spring of 2004 (two years post-hatch) with 88% of the population being observed to release gametes, no mature individuals were observed in either of the LL treated populations and furthermore there was no evidence of gonadal development or elevation in sex steroids (testosterone, estradiol-17β or calcium). The application of LL appeared to directly stimulate the growth rate of haddock (e.g. 14 to 27% increase in weight thermal growth coefficient) and improve food conversion rates. At the end of the trial there was an approximate 50% increase in wet weight (SNP: 647 ± 53 g, Jan LL: 982 ± 34 g and July LL 985 ± 33 g), however no significant difference in weight in relation to the length of LL exposure was observed. Plasma melatonin analysis revealed that the natural diel rhythm had been inhibited in both LL treated populations. Along with highlighting the similarity in reproductive entrainment between haddock and other gadoids, these results demonstrate how photoperiod manipulation could be used as a management strategy to improve growth performance in farmed haddock stocks. 相似文献
5.
The safety and efficacy of emamectin benzoate, administered in-feed to Atlantic salmon smolts, Salmo salar L., held in freshwater, was evaluated as a preventative treatment against sea lice, Lepeophtheirus salmonis, following transfer of fish to seawater. In the safety study, salmon smolts held in freshwater were fed with diets containing emamectin benzoate at nominal doses of 0 (control), 50 (recommended dose) and 250 (5× recommended dose) μg kg−1 fish day−1 for 7 days (days 0–6). Actual dose rates, based on measured concentrations of emamectin benzoate in feed, differences in fish weight, and feed consumed, were 0, 54, and 272 μg kg−1 day−1, respectively. On day 9, fish were transferred to seawater and observed for 14 days. No differences in feeding response, coordination, behaviour, gross and histological appearance were observed between control fish and those that received 54 μg kg−1 day−1. Among smolts that received 272 μg kg−1 day−1, approximately 50% exhibited darker coloration, and one fish (1%) exhibited uncoordinated swimming behaviour. No pathognomonic signs of emamectin benzoate toxicity were identified. In the efficacy study, smolts held in freshwater were fed an unmedicated ration (control group) or emamectin benzoate at 50 μg kg−1 day−1 (treated group) for 7 days (days 0–6). On day 9, fish were re-distributed to eight seawater tanks, each holding 30 control and 30 treated fish. On days 28, 56, 77 and 109, respectively, control and treated fish in two tanks were challenged with L. salmonis copepodites. When lice in each group reached chalimus stage IV, fish were sampled and the numbers of lice were recorded. Fish challenged at day 109 were sampled for the second time when lice were at the adult stage. Efficacy was calculated as the reduction in the mean number of lice on treated fish relative to the mean on control fish. Treatment with emamectin benzoate resulted in an efficacy of 85.0–99.8% in fish challenged at days 28–77, from the start of treatment, and lice counts were significantly lower (P<0.001) on treated fish than on controls. When fish challenged at day 109 were sampled at day 128, efficacy was 44.3%, but survival of chalimus to adult lice on treated fish was lower, and at day 159, efficacy had increased to 73%. These results demonstrate that treatment of salmon smolts with emamectin benzoate in freshwater was well tolerated and highly effective in preventing sea lice infestation following transfer of fish to seawater. 相似文献
6.
The potential of bacteriophage therapy to control bacterial disease in farmed fish was tested using, as an example, furunculosis of Atlantic salmon, caused by Aeromonas salmonicida subsp. salmonicida. In vivo testing with Atlantic salmon and rainbow trout (Oncorhynchus mykiss Walbaum) showed no adverse effects, with bacteriophage generally cleared within 96 h of administration by either intraperitoneal (i.p.) injection or oral in-feed. Juvenile Atlantic salmon were administered a combination of bacteriophage O, R and B (1.9 × 108 pfu fish− 1) by i.p. injection, after they had been challenged with A. salmonicida subsp. salmonicida 78027, also by i.p. injection. The fish that were injected with bacteriophage immediately after challenge died at a significantly slower rate then those that were either not treated with bacteriophage, or treated 24 h post-challenge. However, the end result (100% mortality) was not affected. In further experiments the effects of oral (1.88 × 105 pfu g− 1 fish− 1 daily for 30 days), bath (1.04 × 105 ml− 1 daily for 30 days) and i.p. (6.25 × 107 pfu fish− 1) phage treatment to control furunculosis in experimentally infected Atlantic salmon were compared with antibiotherapy (treatment with 10 mg kg− 1 bw− 1 day− 1 oxolinic acid for 10 days), using an indirect cohabitation challenge. No protection was offered by any of the bacteriophage treatments, compared to the positive challenge group, although significant protection was offered by the oxolinic acid treatment. Analysis of samples taken from the trials demonstrated that bacteriophage were correctly administered to the fish and, on occasion, were isolated from fish that had succumbed to furunculosis. It was also shown that bacteriophage resistant A. salmonicida subsp. salmonicida isolates could be recovered from mortalities in all the treatment groups. The results suggest that, although there were no safety problems associated with the approach, furunculosis in Atlantic salmon is not readily controllable by application of bacteriophage. 相似文献
7.
Growth performance and food conversion efficiency (FCE) were investigated in juvenile spotted wolffish ( Anarhichas minor Olafsen), mean (S.D.) initial weight 15.7 (4.8) g, reared at four levels of carbon dioxide (CO 2(aq)) for 10 weeks at 6 °C and 33‰. CO 2 levels averaged 1.1 (control), 18.1 (low), 33.5 (medium) and 59.4 (high) mg l −1, with corresponding pH values of 8.10, 6.98, 6.71 and 6.45, respectively. In addition, kidneys from sampled fish were examined macroscopically for gross signs of calcareous deposits, i.e. nephrocalcinosis, at the start and end of the experiment. Growth was significantly reduced at the highest concentration ( P<0.0001), as compared to all other groups, while no overall differences in growth rate or mean weight were seen in the range of 1.1–33.5 mg CO 2 l −1 at the end of the experiment. Daily feeding rates and total food consumption were reduced at the highest concentration ( P<0.001), whereas food conversion efficiency did not vary significantly between groups. Plasma chloride levels displayed a significant decrease with increasing CO 2 levels, from 151.3 mmol l −1 (1.1 mg CO 2 l −1) to 128.3 mmol l −1 (59.4 mg CO 2 l −1) at the end of the experiment, whereas plasma osmolality in the high CO 2 group was significantly higher compared to the control group at the end of the experiment (371.4 and 350.8 mOsmol kg −1, respectively). Nephrocalcinosis was observed in all groups at the end of the experiment, but was most pronounced in the medium and high CO 2 group. 相似文献
8.
The culture of the mulloway ( Argyrosomus japonicus), like many other Sciaenidae fishes, is rapidly growing. However there is no information on their metabolic physiology. In this study, the effects of various hypoxia levels on the swimming performance and metabolic scope of juvenile mulloway (0.34 ± 0.01 kg, mean ± SE, n = 30) was investigated (water temperature = 22 °C). In normoxic conditions (dissolved oxygen = 6.85 mg l − 1), mulloway oxygen consumption rate (M·o 2) increased exponentially with swimming speed to a maximum velocity ( Ucrit) of 1.7 ± < 0.1 body lengths s − 1 (BL s − 1) ( n = 6). Mulloway standard metabolic rate (SMR) was typical for non-tuna fishes (73 ± 8 mg kg − 1 h − 1) and they had a moderate scope for aerobic metabolism (5 times the SMR). Mulloway minimum gross cost of transport (GCOT min, 0.14 ± 0.01 mg kg − 1 m − 1) and optimum swimming velocity ( Uopt, 1.3 ± 0.2 BL s − 1) were comparable to many other body and caudal fin swimming fish species. Energy expenditure was minimum when swimming between 0.3 and 0.5 BL s − 1. The critical dissolved oxygen level was 1.80 mg l − 1 for mulloway swimming at 0.9 BL s − 1. This reveals that mulloway are well adapted to hypoxia, which is probably adaptive from their natural early life history within estuaries. In all levels of hypoxia (75% saturation = 5.23, 50% = 3.64, and 25% = 1 .86 mg l − 1), M·o 2 increased linearly with swimming speed and active metabolic rate (AMR) was reduced (218 ± 17, 202 ± 14 and 175 ± 10 mg kg − 1 h − 1 for 75%, 50% and 25% saturation respectively). However, Ucrit was only reduced at 50% and 25% saturation (1.4 ± < 0.1 and 1.4 ± < 0.1 BL s − 1 respectively). This demonstrates that although the metabolic capacity of mulloway is reduced in mild hypoxia (75% saturation) they are able to compensate to maintain swimming performance. GCOT min (0.09 ± 0.01 mg kg − 1 m − 1) and Uopt (0.8 ± 0.1 BL s − 1) were significantly reduced at 25% dissolved oxygen saturation. As mulloway metabolic scope was significantly reduced at all hypoxia levels, it suggests that even mild hypoxia may reduce growth productivity. 相似文献
9.
The aim of this study was to analyze the effect of a probiotic bacterium, Enterococcus faecium ZJ4 on growth performances and immune responses of tilapia ( Oreochromis niloticus). The tilapias were treated with E. faecium ZJ4 at a final concentration of 1 × 10 7 cfu ml − 1 in aquaria water every 4 days. Six aquaria with three replicates for treated and controls were used. After 40 days, the tilapias supplemented with the probiotic showed significantly better final weight and daily weight gain (DWG) than those fed the basal diet (Control) ( P < 0.05). There was no remarkable difference ( P > 0.05) in the total serum protein, albumin content, globulin concentration and A/G ratio between the treated and control tilapias. The result of lysozyme activity assay was similar to these biochemical indexes. However, the complement component 3 content, myeloperoxidase (MPO) activity and the respiratory burst activity of blood phagocytes were higher ( P < 0.05) in E. faecium treated tilapias (trial 1) than the controls. 相似文献
10.
A study was conducted to evaluate the effect of partial replacement of dietary fish meal by crystalline amino acids on growth performance, feed utilization, body composition and nitrogen utilization of turbot juveniles. Four diets were formulated to be isolipidic (12% DM) and isonitrogenous (8% DM). A fish meal based diet was used as control. In the experimental diets, a crystalline amino acid (AA) mixture was used to partially replace fish meal, corresponding to a non-protein nitrogen content of 19, 37 and 56%, respectively (diets 19AA, 37AA and 56AA, respectively). The overall amino acid profile of the experimental diets resembled that of the whole-body protein of turbot. Each experimental diet was fed to triplicate groups of 20 fish (initial body weight of 31.8 g) twice daily to apparent satiation for 42 days. During the trial water temperature averaged 18 °C. Final body weight, weight gain (g kg ABW− 1 day− 1) and specific growth rate were not different between the control and 19AA diet but significantly decreased with the increase of crystalline-AA inclusion from 19 to 56%. Feed intake and feed efficiency of fish fed the control and diet 19AA were similar and significantly higher than those of fish fed the 56AA diet. At the end of the growth trial, there were no significant differences in whole-body composition among groups. Hepatosomatic index was also unaffected by dietary treatments. Nitrogen retention (g kg ABW− 1 day− 1) of fish fed the control and the 19AA diets were similar and significantly higher than that of fish fed the other diets. Expressed as a percentage of the nitrogen intake, N retention was significantly higher with the control than with the 37AA and 56AA diets. Daily ammonia excretion (mg kg ABW− 1 day− 1) of fish fed the control diet was significantly higher than that of fish fed the 37AA and 56AA diets, while daily urea excretion (mg kg ABW− 1 day− 1) did not significantly differ among treatments. Non-fecal nitrogen (ammonia + urea) excretion (mg kg ABW− 1 day− 1) was significantly higher for fish fed the control diet than in those fed the 37AA and 56AA diets. However, as percent of N intake, ammonia excretion and non-fecal N excretion were significantly higher in fish fed the 56AA diet than in those fed the control and 19AA diets. Specific activity of glutamate dehydrogenase, alanine and aspartate aminotransferases did not significantly differ among experimental groups. In conclusion, in diets with an overall amino acid profile resembling that of the whole-body protein of turbot, crystalline-AA may replace 19% of dietary protein without negatively affecting growth performances or feed utilization efficiency. However, higher protein replacement levels of protein-bound-AA by crystalline-AA severely depressed growth performance. 相似文献
11.
The aim of this study was to investigate the effect of continuous light at different stages during the production cycle of Atlantic halibut Hippoglossus hippoglossus L. on growth, age at first maturity, endocrine parameters and flesh quality. A group of juvenile halibut [mean (SD), initial weight 191.3 g (44.7)] was reared in indoor tanks under ambient temperature conditions for 38 months until harvesting (mean final weight, 4.6 kg). The entire photoperiod experiment was divided into four phases, where the fish in each phase were exposed to either natural photoperiod (62°33'N) or continuous light (L). Thus, the following five photoperiod combinations were tested: (a) Control group (NNNN), (b) Group 2A (NLNN), (c) Group 2B (NNLN), (d) Group 2C (NNNL) and (e) Production group (LNNN). Exposure to continuous light stimulated growth, and the final mean weights of Groups 2A and 2B were 23% and 11% higher than those of the Control group (NNNN). The final plasma 11-ketotestosteron levels were lower in Groups 2A (2.94 ng mL −1) and 2B (2.46 ng mL −1) compared with the Control (5.29 ng mL −1), Group 2C (5.09 ng mL −1) and the Production group (4.78 ng mL −1) during spring 2007 (age 4 years), indicating higher age at first maturity in Groups 2A and 2B. Photoperiod regime had only a minor, and transient, effect on flesh-quality traits of the fish, whereas a significant seasonal effect was seen with a tendency towards increased gaping, lower pH, lower hardness and lower shear force in July compared with December and March. 相似文献
12.
Behavioral and ventilatory parameters have the possibility of predicting the stress state of fish in vivo and in situ. This paper presents a new image-processing algorithm for quantifying the average swimming speed of a fish school in an aquarium. This method is based on the alteration in projected area caused by the movement of individual fish during frame sequences captured at given time intervals. The image enhancement method increases the contrast between fish and background, and is thus suitable for use in turbid aquaculture water. Behavioral parameters (swimming activity and distribution parameters) and changes in ventilation frequency (VF) of tilapia ( Oreochromis niloticus) responded to acute fluctuations in dissolved oxygen (DO) which were monitored continuously in the course of normoxia, falling DO level, maintenance of hypoxia (three levels of 1.5, 0.8 and 0.3 mg l −1) and subsequent recovery to normoxia. These parameters responded sensitively to acute variations in DO level; they displayed significant changes ( P < 0.05) during severe hypoxia (0.8 and 0.3 mg l −1 level) compared with normoxic condition, but there was no significant difference under conditions of mild hypoxia (1.5 mg l −1 level). There was no significant difference in VF between two levels of severe hypoxia 0.8 and 0.3 mg l −1 level during the low DO condition. The activity and distribution parameters displayed distinguishable differences between the 0.8 and 0.3 mg l −1 levels. The behavioral parameters are thus capable of distinguishing between different degrees of severe hypoxia, though there were relatively large fluctuations. 相似文献
13.
Integrated mariculture is a feasible method to maintain sustainable and high productivity of aquaculture. The choice of cultured animals and biofilters in the integrated system has to be made on the basis of their nutrient release rates and the clearance rate of each component of the system. We are examining the nutrient release rates among fish (mangrove snapper, Lutjanus russeli, and sea perch, Abudefduf septemfasciatus), abalone ( Haliotis diversicolor), scallops ( Chlamys noblis), and green mussels ( Perna viridis) in the laboratory. Fish feed is the major sources of inorganic nutrient input in fish farms. The orthophosphate and ammonia release rates of minced trash fish (1593 μg P g −1 day −1 and 150 μg N g −1 day −1) were respectively 6–12 times and 4–88 times higher than those of cultivated fish. Mangrove snapper had the overall highest nutrient release rate, followed by sea perch, abalone, scallops, and mussels for nitrite and nitrate; and followed by abalone, sea perch, mussels, and scallops for orthophosphate and ammonium. Among mollusks, abalone had the highest orthophosphate (162 μg P g −1 day −1), nitrate (1.4 μg N g −1 day −1), nitrite (1.6 μg N g −1 day −1) and ammonium (25.0 μg N g −1 day −1) release rates per gram wet weight per day. Abalone released large amounts of orthophosphate, nitrite and nitrate in the experiment. Scallops and green mussels had low nutrient release rates. 相似文献
14.
The growth and survival of three size classes of wild caught western rock lobster, Panulirus cygnus (post-pueruli: mean 2.14 ± 0.07 g, 13.2 ± 0.1 mm CL; year 1: post-settlement juveniles, 57.1 ± 1.1 g, 38.7 ± 0.28 mm CL; and year 2 post-settlement juveniles, mean 138.2 ± 2.26 g, 51.9 ± 0.25 mm CL) were examined at combinations of two stocking densities (post-pueruli: 50 and 100 m − 2; year 1: 11 and 23 m − 2; year 2: 10 and 19 m − 2) and two shelter types (a novel rigid plastic mesh shelter or bricks) over a period of 6 months. Survival of lobsters held at the lower densities (90–95%) was significantly greater than for lobsters held at higher densities (post-pueruli = 78%, year 1 = 86%, year 2 = 88%). Post-pueruli survival was significantly higher in tanks with mesh shelters (91.7%) than brick shelters (75.8%) with a similar trend exhibited by year 1 and year 2 lobsters. Densities tested did not significantly affect lobster growth for any size class. Growth of post-pueruli was considerably higher in tanks with mesh shelters (641.7% weight gain; specific growth rate 1.07 BW day − 1) ( p < 0.05) but there was no difference in the growth of year 1 and year 2 lobsters between mesh and brick shelters. Feed intake (g pellet dry matter lobster − 1 day − 1) was not significantly different between densities. This study has shown that P. cygnus is well suited for aquaculture based on the collection and ongrowing of wild caught pueruli, as this species exhibits good survival at high densities (up to 100 m − 2) without adverse effects on growth, and shows no captivity-related health problems. We recommend mesh shelters, with stocking densities of 50 m − 2 for post-pueruli and between 20 and 25 m − 2 for year 1 and year 2 juveniles, to maximise survival and production. 相似文献
15.
The nutritional response of Litopenaeus schmitti larvae to substitution of Chaetoceros muelleri by Spirulina platensis meal (SPM) was evaluated. The substitution levels (S) were 0%, 25%, 50%, 75% and 100%, dry weight basis. Final larval length (FL) ranged from 1.98 to 3.16 mm for the different substitution levels. There was a significant relationship between S and FL, described by the following quadratic equation: FL = 2.853 + 0.01598 S − 0.000233 S2. The substitution level ( S) yielding maximum FL was 34.2%. Development index (DI) values ranged from 2.84 to 3.93 and were dependent on substitution level. The corresponding equation was DI = 3.799 + 0.00945 S − 0.000189 S2 ( P < 0.01). Maximum DI was obtained at 25.0% substitution. Survival was high (82–87%) and no significant differences were found between treatments. Protein digestibility of either microalgae was high, with 92% for SPM and 94% for C. muelleri, with no significant differences between them. The results in this study indicate that an adequate balance of nutrients in relation to the requirements of the species is critical. To simultaneously improve FL and DI, a 30% substitution of C. muelleri by SPM is suggested. This is equivalent to feeding 0.15 mg larvae − 1 day − 1 dry weight basis of a 70% C. muelleri/30% SPM diet, representing 0.078 mg protein larvae − 1 day − 1, 0.026 mg lipids larvae − 1 day − 1 and 2.732 J larvae − 1 day − 1. 相似文献
17.
Atlantic halibut, Hippoglossus hippoglossus L., eat larger satiation meals (mean 11.7% body weight) than lemon sole, Microstomus kitt (Walbaum), (2.6% body weight). Total gut clearance time was about 120 h for halibut and 72 h for lemon sole. There are marked differences in feeding behaviour between the two species; halibut feed in midwater and require several body lengths of approach swimming before taking large items of food, while lemon sole eat only off the bottom. In shared tanks, no aggressive interaction was observed. A duoculture system holding small numbers of lemon sole with the more valuable halibut is recommended as a means of minimizing food waste and tank fouling. Oxygen uptakes of 0.07-0.11 ml O 2 g fish wt −1 h −1 (depending on nutritional state) were recorded for the two species. Ammonia nitrogen outputs were also similar. Starved halibut excreted 2.32 μg N g −1 h −1, fed animals 5.08 μg N g −1 h −1. The corresponding values for lemon sole were 3.26 μg N g −1 h −1 and 6.37 μg N g −1 h −1, respectively. 相似文献
18.
The effects of feed intake level on energy and nitrogen partitioning were studied in juvenile Atlantic cod (250 g) fed two fish meal based diets differing in protein and lipid content (54:31 and 65:16) at 10 °C. Replicate groups of cod were feed deprived for 32 days or fed one of the two diets at 25, 50, 75 or 100% of group satiation for 60 days. Feed intake and oxygen consumption were measured daily and weights and chemical composition of carcass, liver, viscera and whole body were measured at start and end. Diet digestibilities were assessed in a separate experiment. The whole body and carcass growth rates at a given feed intake did not differ between dietary groups, but the liver grew faster in the fish fed the low protein diet, resulting in higher hepatosomatic indices at the end of the experiment in the groups fed this diet. The efficiency of utilisation of digestible nitrogen for growth (kDNg) was higher for the low protein diet (0.73 ± 0.02) than for the high protein diet (0.53 ± 0.05), resulting in higher nitrogen retention at a given nitrogen intake. No difference in percentage nitrogen retention was seen in full-fed fish however (31.2 ± 2.5 and 28.4 ± 1.6% for the low protein and high protein diets, respectively). This can be explained by higher nitrogen intake in the fish fed the high protein diet, resulting in a smaller proportion of the intake being used for maintenance. There was no difference in energy utilisation between dietary groups. The digestible energy requirement for maintenance (DEmaint) was 53.8 ± 0.9 kJ kg− 1 d− 1 (42.3 ± 0.7 kJ kg− 0.8 d− 1) and the utilisation efficiency for growth (kDEg) was 0.80 ± 0.02. The energy retention in full-fed fish was 31.3 ± 3.5 and 31.7 ± 1.0% for the low protein and high protein diets, respectively. The deposited energy was distributed in approximately equal proportions in the liver and carcass, whereas viscera accounted for a minor proportion. At a given energy intake, the fish fed the high protein diet deposited more energy in the carcass and less in the liver than did those fed the low protein diet. 相似文献
19.
Photoperiod enhancement of growth is becoming an area of increasing interest as a means of enhancing rainbow trout production efficiency in commercial practice. This paper examines the possible implications of shortening periods of constant light (LL) exposure on rainbow trout growth during autumn–spring grow-out under ambient water temperatures in freshwater to portion size. Triplicate groups of juvenile all-female rainbow trout were permanently exposed to LL in October, November, December or January. Growth was monitored and compared with those maintained under a simulated natural photoperiod (SNP) until the following May. Permanent exposure to LL (all treatments) resulted in significantly greater weight gain of rainbow trout than those under SNP. Furthermore, greatest growth was achieved when fish were left permanently exposed to LL from October. These findings suggest there may be implications for fish farmers if the period of photoperiod exposure is reduced, or timing of application is not considered with regards to ambient water temperatures. 相似文献
20.
Rings on 323 sectioned otoliths (sagittae) were used to determine the ages of greater amberjack, Seriola dumerili, sampled from headboats and commercial handline vessels operating out of ports from North Carolina through the Florida Keys. Age and growth determinations were difficult. Rings were identified and counted on 71% of the samples, but measurements could be made on only 48%. The oldest fish examined was 17 years old and was 1552 mm total length (TL). Back-calculated mean lengths at annulus formation were 366, 873, 1207 and 1471 mm TL for ages 1, 5, 10 and 15, respectively. The von Bertalanffy equation describing theoretical growth for TL was Lt = 1648(1 − e−0.119(t + 1.230)), where T = years. The equation using fork lengths (FL) was Lt = 1514(1 − e−0.115(t + 1.178)). The weight-length relationship for greater amberjack was W = 7.2 × 10 −8L2.700, where W is the whole fish weight (in kg), and L is the total length (in mm). Conversion of total length to fork length may be obtained using the equation: FL = −4.807 + 0.887(TL), and fork length to total length: TL = 20.110 + 1.111(FL). Greater amberjack are fully recruited to the fishery by age 8. Estimates of total instantaneous mortality (Z) ranged from 0.60 to 0.65 depending on the year. 相似文献
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