摘要:

We conducted laboratory experiments to determine relationships between water turbidity, piscivory, fork length, and development of the retina in juvenile walleyesStizostedion vitreum. Walleyes 85 mm and longer ate a greater weight and number of fathead minnowsPimephales promelasin turbid water than in clear water. Feeding was inhibited at the highest turbidities (100 and 161 nephelometric turbidity units, NTU) in 1-h feeding trials but not at the highest turbidity (121 NTU) in 4-h trials. In contrast, walleyes in the shorter length-group (≤75 mm) fed at approximately the same rate in clear and turbid trials, but consumption was inhibited at the two highest turbidities (100 and 161 NTU) used in 1-h trials. The tapetum lucidum was present in the retina of walleyes used in all the experiments. Aggregation of photoreceptor cells in the retina into groups of 20 to 30 (to form macroreceptors) begins when walleyes are approximately 60 mm long. Macroreceptors are believed to increase acuity in dim light. In our experiments, the development of macroreceptors was related to increased feeding efficiency in turbid water. The development of scotopic vision early in life permits walleyes to exploit dimly lit environments not used by other predators.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1991)120<0382:RBTPAD>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

Cytophaga columnarisproduces, in culture, an enzyme that degrades chondroitin sulfates A and C and hyaluronic acid, the complex polysaccharides of connective tissue. This study is the first to demonstrate production of such a tissue-degrading enzyme by this fish pathogen. Partial characterization of the enzyme has shown it to be of the chondroitin AC lyase type that has been described for some other bacteria. No relations were found between the host origin, geographic distribution, and amount of enzyme produced by the different isolates. The enzyme is constitutive, is released into the medium as it is produced, has a molecular weight estimated at 42,600, and has an optimum pH of 6.0. Kinetic studies indicate enzyme specificities in the order chondroitin sulfate A > chondroitin sulfate C > hyaluronic acid. The enzyme showed little or no reaction with chondroitin sulfate B and none with heparin, pectic acid, arabinogalactan, gum guar, or gum acacia. The enzyme was produced by all 16C. columnarisisolates tested in the study but by none of the 13 isolates of non-columnaris, yellow-pigmented bacteria of aquatic origin.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1991)120<0391:COACAL>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

We developed a multiple-regression model for estimating the weight contribution of prey taxa in fish diets. In this method, the counts of prey items are regressed against the total stomach content weight for individual fish in order to estimate the mean weight per individual prey item. Estimates obtained by this method were comparable to those obtained by direct measurement of the weights of individual prey items within each stomach. The multiple-regression method substantially reduced processing time by eliminating the need to sort and weigh individual prey items. Reductions in the labor required to process each stomach allow the investigator to examine a fixed number of fish at lower cost or to examine more fish during a fixed time.

ISSN:0002-8487    

DOI:10.1577/1548-8659(1991)120<0396:NAMTFA>2.3.CO;2

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

ISSN:0002-8487    

DOI:10.1577/1548-8659-120.3.401

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor