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1.
Population size estimates and capture rates by various fishing techniques of mature estuarine bream, Acanthopagrus berda, were determined in the Kosi lakes system using mark-recapture methods. The total population size of mature A. berda was estimated to be 45 257 (95% confidence interval: 31 589-74 429) based on fish recaptured in fish traps and 56 112 (95% confidence interval: 25 505-374 080) using recaptures from recreational anglers. Fish traps were estimated to catch about 5% of the mature population of A. berda annually, while recreational rod and line angling and traditional spearfishing accounted for about 1% and 0.2% of the mature population respectively. Limited mark-recapture data for other species of fishes in the lakes yielded annual capture rates by fish traps ranging from 2.4% to 5.8%. These levels of fishing appear low enough to be sustainable, but evidence from a long-term monitoring programme indicates an increase in overall fishing effort in the Kosi lakes between 1984 and 1996 and a three-fold increase in the proportion of the A, berda population caught annually. However, there is no evidence from available catch per unit effort (CPUE) data that current levels of harvesting of A. berda are unsustainable. This needs to be confirmed through modelling of the A. berda stocks and continued monitoring of CPUE in all components of the Kosi lakes fishery. In the meantime, an increase in fishing effort directed at this species is not recommended.  相似文献   

2.
Ages were estimated for the tropical sparid, Acanthopagrus berda, caught in northern KwaZulu-Natal estuaries. Whole otoliths were used in the age determination. Age estimates were validated by marginal increment analysis and oxytetracycline labelling, which indicated that opaque deposition occurs primarily from September to November each year. The reproducibility of age estimates was described by a coefficient of variation of 10%. The von Bertalanffy growth curve was found to best describe the growth of A. berda. The parameters of the von Bertalanffy growth curve indicated that A. berda in northern KwaZulu-Natal is a slowgrowing species, capable of reaching at least 16 years of age. Longevity of the species, coupled with sex change, late maturation and estuarine dependency, give cause for concern for the continued sustainable utilization of this species.  相似文献   

3.
The gut contents of 313 specimens of Hyporhamphus knysnaensis from Rondevlei were analysed. The total lengths of the collected fish varied between 5,1 and 21,8 cm. It was found that the annual cycle in the occurrence of submerged macrophytes in Rondevlei appears to directly influence the feeding of H. knysnaensis of 9 to 17 cm long. This length- group fed mainly on animal material (mostly amphipods and isopods) in winter and the first half of spring while submerged macrophytes were scarce. After the submerged macrophytes became more abundant, however, the 9 to 17-cm length-group changed to a predominantly plant diet (consisting of Ruppia spiralis and Potamogeton pectinatus). H. knysnaensis between approximately 5 and 9 cm long appeared in summer and fed mainly on animal material (mostly amphipods and isopods). Of the 47 specimens collected in this length-group between December 1978 and March 1979, all had animal material in their gut contents. It was the dominant food in 94% of the specimens and formed 90% of the gut contents. In general, therefore, H. knysnaensis can be considered an omnivore.  相似文献   

4.
The diet of the skink, Eumeces chinensis (Lacertilia: Scincidae), in Xiamen (Amoy), China was examined using stomach analysis during April and May, and its selection of prey size was tested by feeding trials. Insects (primarily Coleoptera, Lepidoptera, and Orthoptera), gastropods and arachnids constituted most of the E. chinensis diet, but earthworms, leeches, crustaceans and fish were also consumed. In the field, male skinks ate more prey items that were 11–20 mm in length than other size classes. When presented with a choice of different‐sized prey in the laboratory, male E. chinensis exhibited a strong preference for prey items 11–20 mm in length over other size classes. The relationship between prey size and handling time was exponential, indicating that there is an upper limit to the ability of E. chinensis to process prey. Mean energy intake for handling different‐sized prey showed that selection of midsizeclass prey items would provide male E. chinensis with the most energy‐efficient prey option. These results indicate that prey size selection in E. chinensis favors maximization of rates of energy intake, which is in agreement with optimal foraging theory.  相似文献   

5.
The distribution of Gelidium pristoides, a commercially important seaweed in South Africa, was investigated on St Croix Island in Algoa Bay. Total area of the midlittoral G. pristoides belt was 4241 m2 and total summer standing crop of this perennial seaweed was 265 kg (dry mass). Monthly numerical composition of G. pristoides epifauna at three sites on St Croix is presented and discussed. Nematodes dominated the epifauna throughout the year with harpacticoids the second most abundant taxon. The presence of nauplius, annelid and Diptera larvae as well as juvenile amphipods and molluscs in the epifauna indicates the role of seaweeds as nursery areas for littoral fauna. G. pristoides epifauna averaged 1,77 x 105 animals m-2. Total summer standing stock of G. pristoides epifauna on St Croix was determined by two methods which yielded 6,4 x 108 and 7,3 x 108 animals respectively.  相似文献   

6.
A number of predator–prey studies show that certain prey demographic classes are targeted over others. The possible mechanisms driving these effects can be two-fold. Firstly, a preference for a certain demographic class results in selective predation by a predator. Secondly, different demographic classes exhibit varied behaviour and thus susceptibility to predation risk. To test these mechanisms, a study was conducted on Samara Private Game Reserve to investigate the potential impact cheetah (Acinonyx jubatus) predation has had on the kudu (Tragelaphus strepciseros) population. Kudu age and sex data were collected across both predator-present and predator-absent sections using a spotlight-count method. Results suggest that juvenile kudu and subadult male kudu are selectively hunted by cheetah. This was reflected in significantly lower proportions of these two demographic classes within the predator-present section (both 6.0%, respectively) compared with the predator-absent section (16.8% and 17.4%, respectively). These findings indicate that the shift in the demographics of the kudu population within Samara could be explained by a combination of these two mechanisms.  相似文献   

7.
Horseshoe crabs, the most well-known example of “living fossils”, are iconic and ecologically important macroinvertebrates in coastal and estuarine ecosystems. Their blood is a crucial resource for manufacturing Limulus or Tachypleus amebocyte lysate to detect bacterial endotoxins or fungal contamination in drug and medical devices. An enhanced understanding of their ecological roles and trophic interactions in the food webs is fundamental to facilitate resource management for the declining populations in Asia. Foraging information of the Asian species, however, is mainly derived from preliminary, scattered reports from a limited number of study locations. In this study, resource utilization, trophic niche dynamics, and trophic interaction of the juvenile tri-spine horseshoe crab, Tachypleus tridentatus (instars 1–12, approximately 0.5–8 years old) across ontogeny was assessed in diversified nursery habitats along the northern Beibu Gulf, China, using carbon and nitrogen stable isotopes. Our results suggest that: (i) T. tridentatus are ecological generalists given the vast range of carbon isotopic values and trophic niche width estimates exhibited between multiple instar groups; (ii) juvenile T. tridentatus across most habitat types predominantly assimilated energy from a variety of basal production sources in the food web, but primarily depended on sedimentary organic matter and seagrass resource pools; (iii) ontogenetic shifts in juvenile dietary proportions were evident, with decreased reliance on sedimentary organic matter, coupled with increased reliance on benthic macroinvertebrate grazers, detritivores, and omnivores with age; and (iv) nearly all juvenile instars occupied similar trophic positions in the food web with slight shifts in trophic position present with increasing size. Our findings indicate that resource availability and ontogenetic diet shifts strongly influence horseshoe crab trophic dynamics, and age should be accounted when formulating habitat conservation measures based on resource use for Asian horseshoe crabs.  相似文献   

8.
Digestion rates were determined for natural prey items offered to each of seven species of sea anemones found at Wooley’s Pool in False Bay and to the single species (Bunodactis reynaudi) recorded at Biouberg on the Atlantic coast of the south-western Cape, South Africa.This was done by examining prey items removed from the coelenterons at regular intervals after feeding and assessing their degree of digestion according to a predetermined scale. There was considerable variation in the gut retention times between different anemone species offered the same prey types, with Actinia equina consistently showing the shortest gut retention times (12 h for amphipods, 15 h for pelecypods and 23 h for isopods). Of the various prey categories tested, amphipods tended to be the most rapidly digested group, while molluscs and echinoderms usually remained in the coelenteron the longest. Mean gut retention times in B. reynaudi, the only species found both in False Bay (17°C) and on the cold west coast (12°C) were markedly longer (72 vs 60 h and 43 vs 30 h for pelecypods and gastropods respectively) at the lower temperature.  相似文献   

9.
Forty-six species were recorded in association with Patella spp., but most of these are casual associates, seeking temporary shelter. The shell surface offers an important substrate for algae.

The amphipod Hyale grandicornis is often associated with Patella, particularly in the juvenile stages. It is a facultative inquiline which vacates its hosts at high tide. The isopods Dynamenella australis and D. scabricula are predominantly associated with limpets and complete their life cycles under limpets. Choice chamber experiments demonstrate their preference for sheltering under limpets. The copepod Scutellidium patellarum is similar, but the association is more marked.

Calliopiella michaelseni (Amphipoda) is commensal and show a preference for certain limpet species. Its colour changes in relation to the host species. Feeding occurs on limpet faeces and algal fragments. The life cycle is completed under the limpet, two reproductive peaks occurring each year. Adults usually occur in pairs and there is a positive correlation between host and amphipod size. Juveniles remain with their parents initially, and then disperse to other limpets. Adult pairs may defend their host, excluding other amphipods. Calliopiella is strongly photonegative and thigmotactic.

The turbellarian Notoplanapatellarum is preferentially commensal with Patella oculus. This can be experimentally demonstrated. It feeds on small Crustacea, including Scutellidium.  相似文献   

10.
The diet of 745 Oreochromis mossambicus (Peters) of less than 0,5 up to 2000 g wet mass, in Hartbeespoort Dam, was determined from stomach content analysis. Samples of fish were selected to cover a whole annual cycle. Small fish fed initially on zoobenthos and zooplankton, but fish with a mass of over 4 g fed increasingly on Microcystis aeruginosa Kutzing and detritus until these food items formed the dominant food source in O. mossambicus over 8 g. Some cannibalism was encountered in fish up to 64 g in the summer months. The ratio of intestinal length to total length of fish ranged from 0,58 in the smaller fish to 11,02 in larger fish and this indicated that there was an ontogenetic adaptation from a carnivorous to a phytoplanktivorous/detritivorous diet. Feeding in juvenile fish studied over 24 h was found to be most intense in the early morning and late afternoon but remained high throughout daylight hours decreasing considerably at night. The daily ingestion rate of food in O. mossambicus in Hartbeespoort Dam was estimated at 453 mg/g of fish. This comprised 45% M. aeruginosa and 55% detritus. It was apparent that of this matter ingested only a small percentage would be assimilated. Oreochromis mossambicus shows feeding and breeding preadaptations which enable it to successfully exploit a lacustrine environment. These adaptations enable it to maintain a large population in Hartbeespoort Dam despite frequent winter mortalities caused by water temperatures below their tolerance limits.  相似文献   

11.
This study investigated vitamin A compounds in the plasma of healthy free‐ranging Central European raptors with different feeding strategies. Plasma samples of nestlings of white‐tailed sea eagle [white‐tailed sea eagle (WTSE), Haliaeetus albicilla) (n = 32), osprey (Pandion haliaetus) (n = 39), northern goshawk (Accipiter gentilis) (n = 25), common buzzard (Buteo buteo) (n = 31), and honey buzzard (Pernis apivorus) (n = 18) and adults of WTSE (n = 10), osprey (n = 31), and northern goshawk (n = 45) were investigated with reversed‐phase‐high‐performance liquid chromatography (RP‐HPLC). In WTSE, northern goshawks and common buzzards retinol were the main plasma component of vitamin A, whilst in ospreys and honey buzzards, 3,4‐didehydroretinol predominated. The median of the retinol plasma concentration in the nestlings group ranged from 0.12 to 3.80 μm and in the adult group from 0.15 to 6.13 μm . Median plasma concentrations of 3,4‐didehydroretinol in nestlings ranged from 0.06 to 3.55 μm . In adults, northern goshawks had the lowest plasma concentration of 3,4‐didehydroretinol followed by WTSE and ospreys. The plasma of all investigated species contained retinyl esters (palmitate, oleate, and stearate). The results show considerable species‐specific differences in the vitamin A plasma concentrations that might be caused by different nutrition strategies.  相似文献   

12.
A 12‐week trial with 120 [(Landrace×Yorkshire)×Duroc] pigs (45.65 ± 1.93 kg) was conducted to evaluate the effects of Astragalus membranaceus, Codonopsis pilosula and allicin mixture (HM) supplementation on growth performance, nutrient digestibility, faecal microbial shedding, immune response and meat quality in finishing pigs. Pigs were allocated to one of three treatments with 0, 0.025% (HM1) and 0.05% (HM2) HM supplementation in a randomized complete block design according to sex and BW. Each treatment contained 10 replications with four pigs (two barrows and two gilts) per pen. Dietary HM resulted in a higher G:F (p < 0.05) than CON group during weeks 7 to 12 and the overall periods. Pigs fed HM2 diet had higher ADG than pigs fed CON diet. Pigs fed HM2 supplementation diet led to a higher (p < 0.05) apparent total tract digestibility (ATTD) of dry matter (DM) and gross energy (GE) than pigs fed CON diet at week 6, while the supplementation of HM led to a higher (p < 0.05) ATTD of DM and GE than pigs fed CON diet at week 12. The faecal E. coli counts were reduced, and Lactobacillus counts were increased by increasing HM supplementation (p < 0.05). Pigs fed HM1 diet had higher (p < 0.05) WBC concentration than those fed CON and HM2 diets at week 6. Pigs fed HM‐supplemented diet had higher (p < 0.05) IgG and IgA concentrations than those fed CON diet at week 12. Pigs fed HM diet noted better (p < 0.05) meat colour and redness value than pigs fed CON diet. Pig fed HM2 reduced (p < 0.05) the lightness value compared with CON group. In conclusion, dietary HM supplementation exerted beneficial effects on growth performance, nutrient digestibility, intestinal microbial balance (increased Lactobacillus counts and decreased E. coli counts), immune response and meat quality.  相似文献   

13.
The purpose of this study was to evaluate the effects of dietary administration of the live yeast, Rhodotorula sp. C11, on growth and disease resistance against Vibrio splendidus infection in juvenile Japanese spiky sea cucumber Apostichopus japonicus. Sea cucumbers were fed diets containing Rhodotorula sp. C11 at 0 (control), 104, 105, and 106 CFU/g of feed for 45 d. There were three replicate tanks per dietary treatment. The specific growth rates were higher in all sea cucumbers treated with Rhodotorula sp. C11 than in the controls. Following a challenge with V. splendidus NB13, the cumulative prevalence and mortality of sea cucumbers fed diets supplemented with Rhodotorula sp. C11 were lower than in animals fed the basal diet. In sea cucumbers fed diets supplemented with Rhodotorula sp. C11 for 42 d, the only viable yeast found in the intestine was Rhodotorula sp. C11, which had counts of 1.58–1.98 × 104 CFU/g. No yeast was isolated from the intestine of animals fed the basal diet. For the colonization study, 20 sea cucumbers from each dietary treatment were removed to separate tanks and fed the control diet from day 16 to day 46. The viable yeast (Rhodotorula sp. C11) counts in the intestine decreased to 60–80 CFU/g by day 37. Moreover, as demonstrated by denaturing gradient gel electrophoresis, Rhodotorula sp. C11 colonization of the intestine could be detected until day 46. The differences in culture and PCR-denaturing gradient gel electrophoresis may be due to differences in the sensitivity of both methods. The present result showed that Rhodotorula sp. C11 was able to successfully colonize the intestine of juvenile Japanese spiky sea cucumbers by dietary supplementation, which improved its growth and disease resistance.

Received August 11, 2014; accepted November 14, 2014  相似文献   


14.
The objective of the present study was to assess the feeding effects of garlic leaf on microbial N supply (MNS), turnover rates of plasma phenylalanine (PheTR) and tyrosine (TyrTR) and whole body protein synthesis (WBPS) in sheep. The sheep were fed either mixed hay (Hay‐diet, as control) or hay plus garlic leaf diet (GL‐diet, at a ratio of 9:1) in a crossover design each for a 21 day period. The isotope dilution method using [2H5]Phe and [2H2]Tyr was performed on the 21st day of each dietary treatment. Nitrogen intake remained similar between the diets and N absorption and N digestibility were higher (P < 0.05) in the GL‐diet than Hay‐diet. Total purine derivatives excretion and MNS were greater (P < 0.05) in the GL‐diet than the Hay‐diet. Plasma PheTR tended to be higher (P = 0.06) during GL feeding and TyrTR did not differ between the diets. Further, WBPS tended to be greater (P = 0.05) for the GL‐diet compared with the Hay‐diet. Hence, the present results suggest that garlic leaf may have positive effects on N metabolism by influencing MNS in sheep and could be used as a potential ruminant feed in the future.  相似文献   

15.
The effects of supplementing a basal diet of guineagrass (Panicum maximum cv Ntchisi) (diet 5) with Stylosanthes guianensis (diet 1), Lablab purpureus (diet 2), Aeschynomene histrix (diet 3) and Centrosema pubescens (diet 5) on West African dwarf goats were evaluated. Parameters measured were feed intake, nutrient digestibility and nitrogen balance. Voluntary intake (g/kg W0.75/day) of dry matter (DM) 138.73, crude protein (CP) 25.86, neutral detergent fiber (NDF) (96.29) and acid detergent fiber (ADF) (65.73) of diet 1 were not significantly different (P > 0.05) from the other diets with legume supplements. The feed intake of goats on diet 5 was lower (P < 0.05), having corresponding values of DM (108.21), CP (17.33), NDF (77.68), and ADF (53.55). Weight gain (g/day) differed (P < 0.05) in goats placed on the diets. The lowest weight gain was obtained in diet 5. The digestibilities of DM, CP, ADF and acid detergent lignin (ADL) differed (P < 0.05) in diet 1–5 except for NDF digestibility. Nitrogen balance (g/kg W 0.75/day) ranged from 0.29 in diet 5 to 0.83 in diet 2 (P < 0.05). Similarly, nitrogen retention percentage was highest in diet 2 (35.17), with the lowest value in diet 5 (20.71). It could be concluded that a diet consisting of Panicum maximum with Lablab purpureus supplementation gave the highest performance in weight gain, nitrogen digestibility and nitrogen utilization. However, any of the herbaceous legumes in this study would lead to increased productivity of ruminant livestock.  相似文献   

16.
The purpose of this study was to investigate the effects of feeding Bacillus subtilis on rumen fermentation, blood metabolites, nutrient digestibility, and energy and nitrogen balances in non-lactating crossbred (Holstein-Friesian × Bos indicus) cows. Four cows were assigned to the control and B. subtilis diets in a crossover design, and respiratory and metabolic experiments were conducted. For the B. subtilis diet, B. subtilis DSM15544 spores were added at the rate of 1.0 × 1010 CFU/head/day to the control diet. At 4 hr after feeding, cows fed the B. subtilis diet had increased levels of i-butyric acid in the rumen fluid and tended to have lower concentrations of plasma non-esterified fatty acids when compared with cows fed the control diet. This suggests that feeding B. subtilis could improve energy efficiency. However, there was no effect on energy retention in this study. Although there were no effects on nutrient digestibility, nitrogen balance, or methane production, heat production was significantly higher in cows fed the B. subtilis diet than in those fed the control diet.  相似文献   

17.
The study of predator–prey interactions is commonly analyzed using functional responses to gain an understanding of predation patterns and the impact they have on prey populations. Despite this, little is known about predator–prey systems with multiple prey species in sites near the equator. Here we studied the functional response of cougars (Puma concolor) in relation to their main prey, armadillo (Dasypus novemcinctus), coati (Nasua narica) and white‐tailed deer (Odocoileus virginianus). Between 2004 and 2010, cougar scats were collected along 5 transects to estimate the consumption of different prey species. A relative abundance index (RAI) was calculated for each prey species and cougar using 18 camera traps. We compared Holling type I, II and III functional response models to determine patterns in prey consumption based on the relative abundance and biomass of each prey species consumed. The 3 main prey species comprised 55% (armadillo), 17% (coati) and 8% (white‐tailed deer) of the diet. Type I and II functional responses described consumption of the 2 most common prey species armadillos and coati similarly well, while a type I response best characterized consumption of white‐tailed deer. A negative correlation between the proportions of armadillo versus coati and white‐tailed deer biomass in cougar scats suggests switching to consume alternative prey, confirming high foraging plasticity of this carnivore. This work represents one of the few studies to compare functional responses across multiple prey species, combined with evidence for prey‐switching at low densities of preferred prey.  相似文献   

18.
Eighteen Duroc × Landrace × Yorkshire barrows, with an average initial body weight (BW) of 75.4 ± 2.0 kg, were randomly allotted to one of three diets with six replicates per treatment for 25 days. The diets comprised a normal protein diet (NP, 14.5% crude protein), a low crude protein diet supplemented with 0.27% alanine (LP + Ala, 10.0% crude protein), or a low crude protein diet supplemented with 0.40% leucine (LP + Leu, 10.0% crude protein). The whole‐body protein synthesis rate, whole‐body protein breakdown rate and protein deposition rate in pigs fed the LP + Leu diet were similar to the NP diet (P > 0.05), and both were significantly higher than pigs fed the LP + Ala diet (P < 0.05). The Longissimus muscle area (LMA) of pigs fed the LP + Leu diet was larger than those fed the LP + Ala diet (P = 0.05). In addition, drip loss and intramuscular fat of pigs fed the LP + Ala diet were higher than that of the others (P < 0.05). In conclusion, supplementation of leucine in low protein diet could stimulate protein deposition and improve the meat quality of finishing pigs more than an alanine‐supplemented one.  相似文献   

19.
Species richness of the intertidal macroinfauna of exposed sandy beaches around South America is reviewed in relation to geographic location. This macroinfauna is dominated by cirolanid isopods (Excirolana), bivalves (Mesodesma and Donax) and opheliid and spionid polychaetes. In general, the upper shore of tropical and subtropical beaches is characterized by crabs (Ocypodidae), whereas on temperate beaches it is dominated by talitrid amphipods and cirolanid isopods. The middle shore is primarily occupied by cirolanids and bivalves, and hippid crabs, bivalves and amphipods dominate the lower beach. Generally, species richness increases from upper to lower beach levels. Studies carried out on exposed sandy beaches of south-central Chile (ca. 40°S) show that different beach states harbour differences in species richness, with the greatest species richness on dissipative beaches, and the least on beaches with reflective characteristics, a pattern also observed in Uruguay.  相似文献   

20.
The present study examined the effects of substituting kraft pulp (KP) with corn silage (CS) on dry matter intake (DMI), ruminal mat and rumen fermentation characteristics, and rumination. Four non‐lactating, rumen‐cannulated Holstein cows were fed a CS diet comprising 36% grass silage (GS) and 64% CS or a KP diet comprising 36% GS, 57% KP, and 7% soybean meal. DMI was significantly lower in cows fed the KP diet than in those fed the CS diet (p < 0.05), whereas rumination time did not significantly differ between the treatments. Dry matter content in the rumen immediately before and 3 h after feeding was significantly higher in cows fed the KP diet than in those fed the CS diet (p < 0.05). The consistency and thickness of the ruminal mat did not significantly differ between the treatments. The ruminal mean retention time of feed particles tended to be longer in cows fed the KP diet than in those fed the CS diet (p < 0.10). The ruminal digestion rate of KP was comparable to that of GS and CS. Because ruminal mat was formed and rumination was stimulated, KP was considered to have the equivalent physical effectiveness as CS.  相似文献   

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