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1.
In this work, we investigated the effects of various feeding treatments on the survival and growth of Huso huso and Acipenser persicus larvae during a 20‐day culture period. Three replicate groups (250 fish/replicate) of first‐feeding larvae were fed according to four main feeding regimes: (1) live food (live nauplii of brine shrimp Artemia urmiana); (2) indirect transition (5–7 days live food followed by gradual transition to formulated diet); (3) direct transition (using different combinations of live and formulated diet from the start feeding onwards); and (4) formulated feed (FD) from the start of feeding. In H. huso larvae, combining live food and manufactured diets (co‐feeding) from the first feeding stage onwards (direct transition) resulted in significantly higher weight gain than the other regimes. Survival was significantly higher in H. huso larvae fed solely live food or the direct transition regimes compared with indirect transition and FD. In A. persicus larvae, growth and survival were higher in the indirect transition feeding regime than in the other regimes. On the basis of the results of this study, we recommend co‐feeding of H. huso immediately from the commencement of exogenous feeding, but co‐feeding of A. persicus should start 7 days after prior feeding with live food.  相似文献   

2.
Growth performance and survival of alligator gar (Atractosteus spatula) larvae fed Artemia nauplii, two artificial diets (with different protein content and buoyancy) and a control under starvation at first feeding [5 days after hatching (5 DAH)] were studied. All larvae under starvation (C) died at 10 DAH, while survival was near 60% for the rest of the treatments at the end of the experimental period. By the end of the experimental period morphological variables (total length, snout length, wet weight and dry weight) were better in larvae fed the artificial diets compared to live food. These results were confirmed by means of nucleic acid indexes and digestive enzymatic activity. The importance of the relationship between diet size and snout gape was evidenced from these results. Differences between artificial diets were attributed to different digestibility values. Alligator gar larvae are able to grow and survive satisfactorily when fed artificial diets from the start of exogenous feeding, provided that these have an adequate size, buoyancy and quality.  相似文献   

3.
Alligator gar, Atractosteus spatula, are a new aquaculture species with many aspects about rearing unknown. Alligator gar are cannibalistic during their larval stage and methods to minimize cannibalism should be developed to increase overall survival. Growth and survival were determined for larvae fed pelleted floating food only or fed pelleted floating food supplemented with live Artemia spp. nauplii for the first 7 d of exogenous feeding (5 d after hatching [d.a.h.] to 12 d.a.h.). Total length, weight, condition, and specific growth rate (SGR) was determined at 12 and 20 d.a.h. Fish supplemented with Artemia were larger by 12 d.a.h. and continued to be at 20 d.a.h. than fish fed only floating food. SGR was higher at both 12 and 20 d.a.h. for fish that received the Artemia supplement. Survival was higher for fish supplemented with Artemia (71%) than for the floating food only treatment (43%). Cannibalism was the primary cause of mortalities and was higher in fish fed floating food only (44%) compared to Artemia supplemented fish (19%). Artemia may elicit a stronger feeding response and improve acceptance of pelleted floating foods. Results suggest an improved feeding regime compared to previous feeding regimes used in rearing larval alligator gar.  相似文献   

4.
The study investigated the combined effect of weaning from live feed to a commercial dry pellet at 10, 15, 20, 25 or 30 days posthatching (dph) and co‐feeding for 1, 3 or 6 days on survival and growth of Coregonus peled larvae. Additional groups fed only live Artemia sp. nauplii (ART), and only Biomar LARVIVA ProWean 100 (DRY) were included. A final survival rate of 66.4%–85.5% was observed in groups weaned after 20 dph. Final body weight (BW) and total length (TL) were significantly lower in groups weaned at 10 and 15 dph, regardless of the duration of co‐feeding. Larvae reached 29–37 mg BW and TL of 17.7–19.0 mm in groups weaned at 20, 25 and 30 dph. The recommended minimum duration of feeding with live food, based on these results, is 20 days. Based on the significantly higher yield of larvae weaned after 20 dph irrespective of co‐feeding duration, it can be concluded that abrupt weaning to dry food after 20 days of feeding with live prey can provide adequate production while reducing the effort and costs associated with live feed.  相似文献   

5.
Histological changes of the digestive tract were studied in shi drum (Umbrina cirrosa) from hatching until 41 days post hatching (dph), when the fry had a mean (±S.D.) total length (TL) of 32 ± 2 mm and wet weight (WW) of 0.42 ± 0.07 g. Larvae were reared using the mesocosm technique, the most natural among commercially employed rearing methods for marine larvae. Shi drum opened their mouth at 2 dph (2.78 ± 0.09 mm TL), at which time 90% of the larvae already had an inflated swim bladder. The differentiation of the digestive tract into buccopharynx, esophagus, and anterior and posterior intestine was completed by 3 dph (2.82 ± 0.07 mm TL), 1 day after the onset of exogenous feeding. The alimentary canal started coiling and formed its first loop at 2 dph, while the pancreas and liver were differentiated at 3 dph. Yolk sac reserves lasted until 7 dph (4.3 ± 0.1 mm TL), suggesting a brief period of endogenous and exogenous feeding. The first esophageal goblet cells appeared at 7 dph containing acid mucins and at 8 dph taste buds appeared on the buccopharyngeal epithelium. The stomach was morphologically differentiated at 9 dph (5.5 ± 0.1 mm TL) when gastric glands became abundant in the cardiac region, and the first pyloric caeca appeared at 14 dph (10.1 ± 0.9 mm TL). Supranuclear eosinophilic vacuoles were observed in the posterior intestine between 3 and 11 dph (6.3 ± 0.9 mm TL). Their number decreased as the stomach differentiated, suggesting a change in the protein digestion mechanism. The results of the study suggest a rapid development of shi drum and its digestive system and underline the possibility of weaning larvae to artificial feed even earlier than the 12 dph employed in the present study.  相似文献   

6.
Marine Fish Larvae Feeding: Formulated Diets or Live Prey?   总被引：7，自引：0，他引：7  
In the rearing of larval marine fish, any diet that reduces dependance on live prey production is of technical and economic interest. Weaning juveniles with a completely developed digestive tract to a conventional diet, (i.e., "late weaning") can be successful in any marine fish species. For example, weaning one-month-old sea bass (20 mg) to the study's reference diet, Sevbar, resulted in over 85% survival (40% from hatching) and 1.25 g fish at day 90 (at 19 C)
In contrast, "early weaning" of larvae to special microdiets during the first month is still difficult. The best way to reduce live prey utilization in sea bass is to wean larvae at about 3–4 mg in size (day 20). If weaning could be accomplished 15 days earlier, Artemia savings could be as high as 80%. However, this introduces risks relative to growth retardation (30% weight loss) and lower juvenile quality, including greater size variability and skeletal abnormalities. Similar results have been obtained with commercial microparticles (Fry Feed Kyowa) and experimental microbound diets (MBD) made from raw materials (alginate MBD) or preferably from freeze-dried protein sources (zein MBD).
Total replacement of live prey is still impossible in marine fish. Sea bass larvae fed formulated diets exclusively from first feeding (0.3 mg larval wet weight), or even from their second week of life onwards, exhibited low survival and poor growth. Better results can be obtained when formulated diets are used in combination with live prey from first feeding, although the optimal ratio of live prey to formulated diet is still to be specified.  相似文献   

7.
Two experiments were carried out to test microparticulate diets forweaning hatchery-produced larvae and juveniles of bullseye pufferSphoeroides annulatus. The diets were formulated with differentprotein sources: diet 1 with a combination of decapsulated cysts ofArtemia and fishmeal, and diet 2 with a combination offishmeal, squid, tuna gonad and shrimp meal. In the first experiment60-days-old fish were weaned with the microdiets over five days. Fishsurvival after 11 weeks of feeding was 92% for diet 1, 85%for diet 2, and 95% for the control fish fed Artemianauplii. Once it was determined that bullseye puffer can be adequatelyreared with artificial dry diets, diet 1 was used to test earlier timesfor weaning to reduce the period of Artemia feeding. In thesecond experiment, three different times were tested for initiation ofweaning in sibling fish larvae, i.e., at 29, 34, and 39 days post-hatch.Small differences in weight, length and survival were found amongweaning treatments after 23 days of feeding. When weaned at day 29post-hatch, fish larvae grew from an initial weight of 38.4 mg andlength of 11.1 mm to a final weight and length of 405.7 mg and 25.1 mmrespectively. Final survival in this treatment was 49.3%. Thereduced period of Artemia feeding would provide an economicalalternative for the species to take into consideration for its cultureat commercial scale.  相似文献   

8.
The early foraging ecology of alligator gar (Atractosteus spatula) is poorly documented, with little information available on young‐of‐year food habits or ontogenetic diet shifts. We conducted laboratory experiments to quantify prey selection and foraging behaviours of larval and early juvenile alligator gar (16–80 mm TL) simultaneously offered zooplankton, chironomid larvae and one of three densities of fish prey. The smallest size groups of alligator gar consumed zooplankton almost exclusively, but with increasing size, selection for zooplankton declined and selection for fish prey increased. At higher densities of fish prey, alligator gar exhibited lower selection for zooplankton and positively selected for fish at smaller sizes. Ingestion efficiencies for chironomids were considerably lower than for zooplankton or fish prey, resulting in low rates of consumption and negative selection for chironomids by all size groups of alligator gar. Fish prey elicited a different foraging response from alligator gar than zooplankton or chironomids, as alligator gar pursued and struck at fish over longer distances than for other prey types. With increasing size, alligator gar used a wider vertical range of the water column for foraging, changed their strike tactics and exhibited decreased handling times for zooplankton and fish. These observations indicate that alligator gar undergo several functional and behavioural changes during early ontogeny that facilitate a rapid transition to piscivory, but fish prey density strongly affects prey consumption patterns and the size at which alligator gar transition to piscivory.  相似文献   

9.
The effect of burbot weight (BW) and length (TL) on the efficiency of weaning under controlled conditions was investigated. Growth, survival rate, cannibalism and histological analysis of digestive tract were examined. The experiment lasted 49 days (40–89 days post hatch [DPH]). The fish (BW 0.12 g; TL 14.1 mm) were divided into four groups: a control group (C) exclusively fed Artemia sp. nauplii and groups F40, F47 and F54 that were weaned to dry feed on 40, 47 and 54 DPH, respectively. The highest survival rate was observed in groups C (78%) and F54 (58%). In group F54, similar TL (53.8 mm) and higher BW (1.36 g) at the end of experiment, in comparison with group C (43.9 mm, 0.84 g for TL and BW, respectively), were obtained. At the end of the experiment, the length of enterocytes in groups C and F54 was at a similar level (over 23 μm), whereas in group F47 was significantly lower (approximately 20 μm; P < 0.05). This study for the first time presents successful weaning of the burbot. The data indicate that live food should be offered until the fish reach 25 mm and 0.20 g.  相似文献   

10.
Abstract. European grayling, Thymallus thymallus L., larvae, after hatching, were fed solely on a dry food diet and compared to those fed live zooplankton. After 28 days of rearing at temperatures ranging from 15·0°C to 18·3°C (mean, 16·4°C) fish fed the dry diet reached 0·21 g individual wet weight and 31mm in total length; those fed zooplankton reached 0·13g and 27·5 mm respectively. The survival rate of fish fed the dry diet was higher (56·6%) than that of fish fed the live food (40·7%). Results are discussed in the light of the development of the alimentary tract in the early ontogeny of grayling.  相似文献   

11.
The leopard grouper is an endemic species of the Mexican Pacific with an important commercial fishery and good aquaculture potential. In order to assess the digestive capacity of this species during the larval period and aid in the formulation of adequate weaning diets, this study aimed to characterize the ontogeny of digestive enzymes during development of the digestive system. Digestive enzymes trypsin, chymotrypsin, acid protease, leucine–alanine peptidase, alkaline phosphatase, aminopeptidase N, lipase, amylase and maltase were quantified in larvae fed live prey and weaned onto a formulated microdiet at 31 days after hatching (DAH) and compared with fasting larvae. Enzyme activity for trypsin, lipase and amylase were detected before the opening of the mouth and the onset of exogenous feeding, indicating a precocious development of the digestive system that has been described in many fish species. The intracellular enzyme activity of leucine–alanine peptidase was high during the first days of development, with a tendency to decrease as larvae developed, reaching undetectable levels at the end of the experimental period. In contrast, activities of enzymes located in the intestinal brush border (i.e., aminopeptidase and alkaline phosphatase) were low at the start of exogenous feeding but progressively increased with larval development, indicating the gradual maturation of the digestive system. Based on our results, we conclude that leopard grouper larvae possess a functional digestive system at hatching and before the onset of exogenous feeding. The significant increase in the activity of trypsin, lipase, amylase and acid protease between 30 and 40 DAH suggests that larvae of this species can be successfully weaned onto microdiets during this period.  相似文献   

12.
Problems of limited number of dry feeds as supplement or replacement of live feeds have led to poor larval nutrition in many species of fish. Therefore, the suitability of co‐feeding 8‐day‐old African catfish (Clarias gariepinus) posthatch larvae using live feed (Artemia salina) and formulated dry diet containing freshwater atyid shrimp (Caridina nilotica) during weaning was investigated. The experiment ended after 21 days of culture and respective groups compared on the basis of growth performance, survival, feed utilization and nutrient utilization. Larvae co‐fed using 50%Artemia and 50% formulated dry diet resulted in significantly (P < 0.05) better growth performance, food gain ratio (FGR), protein efficiency ratio (PER) and productive protein values (PPV) than other treatments. The lowest growth performance occurred in larvae weaned using 100% formulated and commercial dry diets. Better survival of over 90% was obtained in larvae weaned using 50%Artemia and 50% dry diet, while abrupt weaning using 100% dry diets resulted in lower survival (<75%). These results support a recommendation of co‐feeding C. gariepinus larvae using a formulated dry diet containing C. nilotica and 50% live feed when weaning is performed after 8 days posthatching period.  相似文献   

13.
Two experiments were conducted to identify appropriate experimental and practical diets for bluegill Lepomis macrochirus and hybrid bluegill L. cyanellus × L. macrochirus reared in aquaria. In the first study, four experimental diets and five commercial diets were evaluated in juvenile hybrid bluegill initially weighing 4.8 g/fish. The experimental diets contained casein (CAS), casein + gelatin (CAWGEL), casein + L‐arginine‐HCI (CAS/ARG), or casein + gelatin + crystalline amino acids (CAS/AA) as sources of crude protein. The commercial diets included three diets formulated to meet the nutritional requirements of rainbow trout Oncorhynchus mykiss and two diets formulated to meet the nutritional requirements of channel catfish Ictalurus punctatus. Each diet was fed twice daily at a rate of 4% of body weigh/d to triplicate groups of fish. At the end of the 8‐wk feeding trial, weight gain was significantly higher in fish fed the best commercial rainbow trout diets (205–217%) compared to fish fed diets formulated for channel catfish (87–104%). Weight gain and feed efficiency (FE) of fish fed the experimental diets (5346% and 0.19–0.32, respectively) were significantly lower than those of fish fed the commercial rainbow trout diets (143–217% and 0.49–0.64, respectively). In the second experiment, the same dietary treatments were fed for 8 wk to juvenile bluegill initially weighing 3.7 g/fish. Each diet was fed twice daily at a rate of 4% of body weight/d to triplicate groups of fish. Weight gain was significantly higher in fish fed commercial trout diets (291–402%) compared to fish fed diets formulated for channel catfish (164–191%). Weight gain and FE of fish fed CAS/ARG were significantly higher than those of fish fed the commercial catfish diets, but significantly lower than those of fish fed the best commercial trout diets. Results of this study indicate that commercial rainbow trout diets are preferable to commercial channel catfish diets for culture of bluegill and hybrid bluegill. More research is needed to identify appropriate experimental diets for this group of fishes.  相似文献   

14.
The tongue sole Cynoglossus semilaevis, an inshore fish in China, has showed great potential in aquaculture recently. However, poor survival was recorded during the period of weaning from live Artemia to artificial diets. In this paper, the influence of co‐feeding larvae with live and inert diet on weaning performance was described. The C. semilaevis larvae were reared at 21 ± 1 °C and fed four different feeding regimes from 6 days post‐hatching (dph): A, Artemia (10 individuals mL?1); B, Artemia (5 individuals mL?1); C, mixed diet (10 Artemia individuals mL?1 and 12 mg L?1 inert diet); and D, mixed diet (5 Artemia individuals mL?1 and 12 mg L?1 inert diet). Rotifers were also supplied in all cases during the first days of feeding. Mixed diets of commercial formulated feed and live prey (rotifers and Artemia) allowed larvae to complete metamorphosis, achieving similar specific growth rate (SGR) (18.5 ± 1.4% and 18.7 ± 1.6%) and survival (40 ± 7.6% and 48.5 ± 6.8%) compared with larvae fed on live feed alone (SGR of 18.3 ± 1.2%, 19.3 ± 1.9% and survival of 41.2 ± 11.3%, 38 ± 4.9%). However, in metamorphosed fish, when live feed was withdrawn on 31 dph, there was significant difference (P < 0.05) in survival and growth among treatments. Metamorphosed fish, previously fed mixture diets during larval stages, had similar survival (62.1 ± 7.6% and 62.8 ± 3.9% for regimes C and D, respectively) but higher than that obtained for fish that previously fed on live feed (49.3 ± 2% and 42.1 ± 3.9% for regimes A and B, respectively) after weaning (day 60). The SGR of weaned fish previously fed live feed was similar (3.1 ± 0.6% and 2.92 ± 0.6% for regimes A and B, respectively) but lower than that recorded for fish that was fed from day 6 to day 30 on the mixed diet (4.5 ± 1.1% and 4.9 ± 0.3% for regimes C and D, respectively). It is suggested that weaning of C. semilaevis from early development would appear to be feasible and larval co‐feeding improves growth and survival.  相似文献   

15.
Successful rearing of larval fish requires culture conditions and feeding strategies matching the ontogenetic status of larvae. This study describes the external morphology and development of organs and structures involved in the feeding process (i.e. sensorial organs, mouthparts and digestive system) from hatching until first feeding in Pacific red snapper. Hatching occurred 26 h after fertilization at 26°C and total length (TL) was 2.45 ± 0.08 mm. The larvae showed an undifferentiated eye and digestive tract. At 48 hah, TL was 3.31 ± 0.12 mm. Yolk and oil globule were still present. The mouth was still closed, but the Meckel's, quadrate, hyoid and hyomandibular cartilages were present. The retina was formed by 5 layers, and a thin layer of pigment epithelium was observed in the outer nuclear layer (ONL). At 70 hah, TL was 3.44 ± 0.22 mm. A remnant of oil globule was still present. The mouth and anus were open. At 93 hah, the number of cones in the ONL of the retina have increased and there was more pigment in the pigment epithelial layer. A joint between Meckel's and the quadrate cartilage and also a joint between the hyomandibular cartilage and the skull were present. The presence of live feed was detected in the digestive tract of these larvae. Based on these observations, the Pacific red snapper larvae is functional to start ingesting live feed between the 3rd and 4th day after hatching.  相似文献   

16.
This study was aimed to develop captive breeding and nurture the young of stonesucker (Garra ceylonensis, Bleeker), a small threatened freshwater fish species endemic to Sri Lanka. Breeding of stonesucker was possible under indoor conditions without hormonal stimulation. They were single spawners having a fecundity of 562±176 eggs per fish (total length of 7.9±0.6 cm) with an egg size of 770–1877 μm. Duration of development stages were, egg to hatchling 36–48 h, hatchling to postlarva stage 3–4 days, postlarva to juvenile stage 5–64 days and adult stage in 300–365 days at 26–28°C. Juveniles exhibited bottom dwelling habit in 70–75 days. Postlarva fed with formulated feed exhibited the highest growth (P<0.05) compared with live diets, Artemia and microworm (Anguillula sp.). Although the juveniles revealed a significantly high growth performance (P<0.05) with swine liver diet up to day 45 compared with formulated feed and combination of detritus and plankton, formulated feed exhibited an increase in growth from day 50. Therefore, formulated feed could be used for rearing of postlarva and juvenile stages without any live feeds.  相似文献   

17.
Summer flounder is a new aquaculture species, the culture of which could be made simpler by the replacement, to the greatest extent possible, of live feed with formulated diets. Previous work has shown that development of the summer flounder stomach can be accelerated by treatment of the larvae with thyroid hormone. Two series of experiments were conducted. In the first experiment, 2-week feeding trials were conducted beginning with fish (which were not treated with thyroid hormone) 14, 21, 28, 35, or 42 days after hatch (DAH) to determine when they could begin to utilize commercially available formulated diets. In the second experiment, two groups of sibling larvae, one treated with thyroid hormone, the other not, were placed in similar 2-week feeding trials at 25, 30 or 35 DAH to test whether survival of thyroid hormone-treated larvae would surpass those of untreated larvae. The first series of experiments demonstrated that the larvae could not effectively utilize the formulated diets until 35 DAH. The second series of experiments indicated that thyroid hormone-treated larvae do not exhibit significantly greater survival than untreated larvae.  相似文献   

18.
Three 30‐day experiments were conducted to evaluate decapsulated Artemia cysts with different quality (high or low hatch‐rate) as food for tench (Tinca tinca L.) larvae from the onset of exogenous feeding. In experiment 1, three diets were tested: Artemia nauplii‐only or cysts‐only for 30 days, and nauplii for the first 7 days and cysts thereafter. The cysts used had 86% hatching rate (high hatch‐rate cysts). The same feeding treatments were replicated in experiment 2 but with low hatch‐rate cysts (10% hatching rate). In experiment 3, five diets were tested: high hatch‐rate cysts only or low hatch‐rate cysts only for 30 days, and nauplii for the first 7, 4 or 2 days and low hatch‐rate cysts thereafter. In overall, survival was high, except with the low hatch‐rate cysts only diet. Feeding tench larvae with cysts resulted in higher growth and lower FCR compared to feeding with live nauplii only. High hatch‐rate Artemia cysts are a suitable food from the onset of exogenous feeding and low hatch‐rate cysts can be successfully used after 2–7 days feeding on nauplii.  相似文献   

19.
Intensive tank rearing of channel catfish (Ictalurus punctatus Rafinesque) fry can be successfully accomplished with commonly available ‘salmonid’ starter diets. Ingredient substitution in starter diets is less important from the cost perspective but growth, survival and health of fish are major concerns. Several combinations of fish meals and animal protein substitutes were evaluated in diet formulations for hatchery rearing of catfish fry. Sub‐optimal thermal conditions were used which are characteristic for the north‐central USA where catfish culture is important for stocking purposes and live‐fish markets. A diet formulated on the basis of menhaden fish meal (29.1%), herring fish meal (25.1%) and animal by‐product mixture (16.38%) gave numerically the highest growth rate after 13 weeks of feeding, although growth reductions in fish fed diets exclusively with mehaden meal (77.6%) as protein or substituted with 50% animal by‐product protein were not significant. Instantaneous mortality rates were the highest between weeks 2 and 4 of rearing and increased almost proportionally with the increased fish meal protein substitution. A diet based on menhaden fish meal had the highest concentration of phosphorus and several other essential minerals, but these were not reflected in the mineral composition of the fish body at the termination of feeding. Among activities of digestive enzymes, trypsin was depressed in fish offered diets with 75–100% fish meal protein replacement. A diet superior in terms of fish performance was defined in the present study and it was concluded that the initial feeding can greatly affect physiological status of juvenile channel catfish.  相似文献   

20.
Juvenile, 1-g Colossoma macropomum (Cuvier) were fed two different diets: one with fish meal and another with soya meal as the main dietary protein source. Both diets were provided at ad libitum feeding level, and at two restricted feeding levels of ～ 80% and 60% of the ad libitum level. The experiment was performed in 30 aquaria, each stocked with 12 fish. For each treatment (two diets X three feeding levels), there were five replicates. Fish were fed three times daily at 0900, 1300 and 1700 h. At sampling days (days 14, 29, 44) in each aquarium in one of these feedings, chromic-oxide-marked feed was used. Shortly after the last meal, fish were weighed and four fish were taken from each aquarium for determination of the chromic oxide content in their digestive tract. Fish fed the fish meal diet attained a higher weight but had a lower body protein content. At the ad libitum feeding level, feed intake of the fish meal diet was higher, but feed and protein utilization efficiency were lower than with the soya diet. However, statistical analysis of the data of both the ad libitum and the two restricted feeding levels revealed that the reduced voluntary feed intake of the soya diet was the cause of its better utilization with ad libitum feeding. There is no evidence that soya protein is more freely available than fish meal protein. The chromic oxide data showed that 15 min after feeding, all of the feed (99.8%) could be traced back in fish fed the lowest feeding level, while at the ad libitum feeding level the recovery was only 72%. These data confirmed the hypothesis that at high feeding levels, considerable amounts of feed remain uneaten. Feed losses were not significantly different between the two diets. The chromic oxide recovery data of the 0900 h and 1300 h feedings showed that the feed passage rate in the digestive tract was similar for the three different feeding levels. Due to the high feed losses at high feeding levels, the relation between feed ration and feed utilization is determined mainly by the percentage of feed losses at the different feed rations.  相似文献   

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