摘要:

Morphologically, the digestive tracts of the king angelfishHolacunthus passerand the Cortes angelfishPomacanthus zonipectusare similar, yet the king angelfish intestine is almost 30% longer than that of the Cortes angelfish. Both pomacanthids have a small mouth with villiform teeth, a short oesophagus, a well‐defined stomach, and a terminal sac at the end of the digestive tract. The terminal sac, the acid pH in the stomach, and the long intestine may facilitate efficient use of seaweed nutrients. Stomach contents were analysed to determine diets and interspecific overlap. Seventy‐one species were found in the stomachs of the king angelfish and 53 in the stomachs of the Cortes angelfish. Because of the wide range of species in their diets, both angelfish must be regarded as omnivorous. The most frequent foods were seaweed and sponges, but for the king angelfish, crustaceans were also important. A cluster analysis was done to determine whether the diets of these fish were similar by sex, size, or season. No similarities were found. Dietary overlap is high in relation to other pomacanth

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1996.tb01477.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

As part of an experimental study of the direct and indirect effects of piscivory on prey fish, the diets of crucian carpCarassius carassiuswere compared across sections of a divided pond; two sections were stocked with crucian carp alone and two with crucian carp plus perchPerca fluviatilis. Analysis of crucian gut contents indicated that the composition of invertebrate prey did not differ in the presencev. absence of perch. However, crucians, particularly small individuals (<10cm) that were most vulnerable to predation, displayed a lower intake of invertebrate prey in sections with perch. Although diet composition differed between crucians caught in inshore v. offshore habitats (with habitat use being related to crucian size and the presence or absence of perch), no clear pattern existed between habitat and total food intake. Overall, the major effects of predators on the diet of crucian carp appeared to be caused by increased ecological density (resulting from confinement of small crucians inshore) and reduced activity levels, rather than simple shifts to safer habitats.

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1996.tb01478.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Endproducts of anaerobic fermentation, volatile fatty acids (VFAs), occur in the intestines of fish but no direct comparisons exist between VFA levels in fish with differing feeding ecologies during different seasons. We measured intestinal concentrations of six types of VFA in the upper and lower intestines of two freshwater omnivores (Cyprinus carpioiandDorosoma cepedianum), and one piscivore (Micropterus salmoides) during the spring, summer and autumn. Acetate occurred in all species, and was highest inM. salmoides. In all species, concentrations were similar between upper and lower guts and higher during the summer. All three species contained anerobic bacteria andC. carpioandD. cepedianumcontained cellulolytic types. Scanning electron microscopy revealed extensive colonization and suggested microbial breakdown of digesta inM. salmoides. In radio‐tracer experiments,C. carpiodosed orally with [2–14C] acetate contained label in liver, muscle and blood tissues. Amounts of intestinal VFA did not appear to increase in species with refractile diets, and low VFA inD. cepedianumsuggests fermentation plays a minimal role in the nutrition of this species. Low levels of intestinal VFA during cool seasons are consistent with the hypothesis that temperature limits fermentation in these Spec

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1996.tb01479.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Both male and femaleParablennius sanguinolentus parvicorniswere ready to mate by the end of May. Seventy‐five per cent of the 1‐year‐old males were mature, but only 25% of the females reached maturity at this age. In females, gonads formed an increasingly greater proportion of the total weight with age, but in males the proportion decreased. A bimodal distribution of gonadosomatic indices classes was observed in 2‐year‐old males (intermediate size), which reflected the lower opportunity that intermediate size males have to spend the ejaculates than have the younger and older males. The liver played an important role in the storage of energy before the reproductive season and reserves were utilized during the breeding season. Physical condition was at its lowest in July in both sexes, but in May, just before the breeding season began, large maturing females had significantly lower eviscerated condition than males. This could be due to females investing in oocyte development, while the priority for the males was to reserve their energy for the parental activities to come. In both males and females, older and bigger animals had lower hepatosomatic and body conditions than you

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1996.tb01480.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

The activity patterns and habitat selection of tench in a shallow eutrophic lake were determined by radio telemetry. Environmental variables, including prey availability, depth and vegetational composition were quantified in order to explain observed patterns of distribution. Tench were generally only active at night, foraging on benthic animal prey, particularly chironomid larvae. Feeding fish clearly selected for particular locations although only weak associations with depth and densities of preferred prey were found. In addition, it appears that fish spent a considerable time searching for prey and travelling relatively large distances in the process, with the result that only relatively few prey were ingested during the course of a night. During daylight, fish were almost completely inactive, resting together in favoured locations and displaying a strong association for the littoral emergent vascular plant,Typha angustifolia. This may be becauseTyphausually grows in relatively deep water and forms stands of relatively widely spaced stems, thus allowing such large fish to penetrate deeply into cover. Management of eutrophic waters to encourage tench should take this habitat preference into account.

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1996.tb01481.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Piscivorous brown troutSalmo truttachange their feeding behaviour depending on prey species, prey size and number of prey eaten. In trout which had eaten fish recently, most had one fish in their stomach, but up to 16 prey fish were found. Individuals of the small‐sized minnowPhoxinus phoxinuswere swallowed chiefly tail first, whereas individuals of the larger Arctic charrSalvelinus alpinuswere taken both head and tail first. The largest charr were swallowed head first. In stomachs containing more than one fish prey, prey orientation was likely to be mixed. For all three types of prey orientation (i.e. tail first, head first and mixed), significant and positive correlations existed between prey length and predator length. The maximum prey size eaten tail first or in mixed orientation was about 70–85% of the size of prey eaten head first, indicating morphological advantages in eating the prey head fi

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1996.tb01482.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Changes in the foraging behaviour due to variation in the body size of the three‐spined sticklebackGasterosteus aculeatuswere investigated. All sizes of fish had a high probability of attacking prey whenever encountered. The probability of eating the prey increased with the size of the fish, as the larger fish had larger jaws and a greater stomach capacity. Therefore, as fish increased in size there was an increase in the probability of successful prey capture. The level of satiation did not have an effect on the prey handling time, which is contrary to other studies and is probably a result of the large prey sizes. The physical size of the prey meant that the handling times were long regardless of the motivational level of the fish. The larger fish took in more energy and at a faster rate, although the time to reach satiation was similar for all fish sizes. The advantage that large fish appear to have in successfully gaining large prey is negated by their greater metabolic requirement. The changes in feeding performance induced by small increases in body size could have important consequences for intraspecific competition, habitat Use and risk of predatio

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1996.tb01483.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Male guppiesPoecilia reticulatacourt almost continuously and often indulge in sneaky mating attempts. Female guppies, on the other hand, devote much of their time to foraging. This paper demonstrates that both sexes reduce their feeding rate in mixed‐sex groups relative to single sex ones and suggests that the decrease is less pronounced for females than for males. Thus males make feeding and mating decisions that are dependent on hunger while female foraging behaviour is constrained by sexual harassment. The observed sex differences in behaviour are a consequence of asymmetrical mating costs in males and female

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1996.tb01484.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Pink salmonOncorhynchus gorbuschafrom odd and even year generations in rivers of Sakhalin Island, Kuril Island, Kamchatka Peninsula, and Alaska were investigated with five informative restriction endonucleases for mtDNA variation. The odd and even generations from the same rivers of South Sakhalin differed greatly. The time of divergence between the two broodlines was estimated at 0.9‐1.1 Myr. The variability of mtDNA in odd year generations was higher than in even year generations and may have been due to‘ founder’ and/or‘ bottleneck’ effects. The differences among river populations within the Sakhalin region in 1991‐1993 were not significant and this confirms the highly migratory nature of pink compared with other Pacific salmon. The mtDNA samples revealed statistically significant differences between regions. The northern populations (Kamchatka, Alaska) were less diverse in number and frequency of haplotypes than the southern populations (Sakhalin). This suggests that pink salmon originated in the Sakhalin‐Kuril region and that a founder effect during the spread of this species may have restricted the mtDNA variability in

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1996.tb01485.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Temporal changes in feeding and growth of immature (1 +), maturing male (1 +), and mature male and female (3+) Arctic charr were studied by monitoring feed intake and growth of individually‐marked fish for over 1 year. The fish were held at a constant temperature (4°C) under conditions of liberal feed supply. Feed intake and growth remained low in the period December‐April, with only 20–60% of the fish having fed on each occasion that feed intake was monitored. Feed intake and growth increased markedly during the late spring and summer, but the increases were delayed by approximately 1–2 months in the immature fish compared with their maturing counterparts. Maturing fish decreased feeding during the late summer and by September there had been an almost complete cessation of feeding. This was reflected in changes in fish body weight and condition, both of which declined from August‐September onwards. By contrast, the immature fish peaked in weight and condition in September, and weight loss during the autumn tended to be less rapid than observed for the maturing fish. The fish appeared to reduce feeding once a‘threshold condition’ of 1–4—1–5 had been attained. It is suggested that the fish may become anorexic once there has been replenishment of the energy reserves required for overwintering and, in the case of maturing individuals, for the completion of gonadal

ISSN:0022-1112    

DOI:10.1111/j.1095-8649.1996.tb01486.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY