My WebLink
|
Help
|
About
|
Sign Out
Home
Browse
Search
7170
CWCB
>
UCREFRP
>
Public
>
7170
Metadata
Thumbnails
Annotations
Entry Properties
Last modified
8/11/2009 11:32:55 AM
Creation date
8/10/2009 12:50:12 PM
Metadata
Fields
Template:
UCREFRP
UCREFRP Catalog Number
7170
Author
Meyer, F. P. and L. A. Barclay
Title
Editor
USFW Year
Series
USFW - Doc Type
1990
Copyright Material
NO
There are no annotations on this page.
Document management portal powered by Laserfiche WebLink 9 © 1998-2015
Laserfiche.
All rights reserved.
/
131
PDF
Print
Pages to print
Enter page numbers and/or page ranges separated by commas. For example, 1,3,5-12.
After downloading, print the document using a PDF reader (e.g. Adobe Reader).
Show annotations
View images
View plain text
I <br />44 ROGER L. HERMAN AND FRED P. MEYER <br />tion, but it is called gas bubble disease or gas bubble <br />trauma. In fish dying from this disorder, obvious gas <br />bubbles develop in the fins, under the skin, or around <br />the eyes. With magnification, bubbles can be seen <br />in the capillaries of the gills. Exophthalmia or pop- <br />eye can occur without visible bubbles. An excellent <br />discussion of problems caused by gas supersatura- <br />tion in water was published by Marking (1987). <br />Fish kills attributable to gas bubble disease can <br />be caused in several ways. If a thermocline forms <br />during warm weather, fish that remain in the cold <br />water below the thermocline sometimes develop gas <br />bubble disease if they move to the warmer surface <br />waters. Water drawn from deep-water intakes of <br />high dams has been subjected to the pressure of the <br />water column and is usually cooler than surface <br />water. When such water is discharged into a surface <br />stream, the hydrostatic pressure is reduced and the <br />rising temperature reduces the solubility of the <br />dissolved gases. Fish subjected to these conditions <br />develop gas bubble disease. If the stream has riffles <br />immediately below the dam, only a short length of <br />stream is affected because turbulence through the <br />riffles releases the excess dissolved gases. Heated <br />discharges from power plants attract fish during <br />cold weather. Movements of fish from cold water <br />into the warm discharge plume sometimes also in- <br />duce gas bubble disease. <br />Nitrogen supersaturation is usually involved in gas <br />bubble disease, but oxygen supersaturation can also <br />cause problems. If aquatic plants (such as the stone- <br />wort, Chara sp.) are abundant and weather conditions <br />are ideal for photosynthesis, the plants may super- <br />saturate the water with oxygen. If the water tem- <br />perature rises or if the pressure changes, fish in the <br />area may develop oxygen-related gas bubble disease <br />just as they do with supersaturation of nitrogen. <br />Other Environmental <br />Stressors <br />Sometimes, an environmental stress may go un- <br />recognized because no direct mortality occurred. <br />Oxygen concentrations below 4 ppm, spawning, <br />migrations, or elevated or depressed water tem- <br />peratures may be significant stressors that reduce <br />the resistance of fish to pathogens. For example, <br />threadfin shad require warm water. If the tem- <br />perature falls to 10° C or lower, the fish become <br />severely stressed and may die; the weakened sur- <br />vivors then frequently develop bacterial or fungal <br />infections that result in a fish kill. Postspawning fish <br />also have reduced resistance to pathogens; it is not <br />uncommon to observe significant numbers of dead <br />fish in spring. Kills of fall-spawning species may <br />also occur. Such kills are usually restricted to <br />adults of a single species, but multiple species may <br />be affected, depending on the chronology of their <br />spawning. <br />Fish kills can also be related to abnormal or <br />unusual characteristics of population structure or <br />density. Occasionally, a single year class of a species <br />may be so successful that it dominates ensuing year <br />classes. Such dominant year classes may be so abun- <br />dant that their numbers exceed the carrying capac- <br />ity of the habitat. When this occurs, individual fish <br />become stunted, are in poor condition, and are highly <br />susceptible to stresses and secondary infections. The <br />collapse of the dominant year class may occur as a <br />large-scale, catastrophic die-off, seemingly associ- <br />ated with a particular pathogen. Although the cause <br />of the fish kill may seem to be disease-related, the <br />primary factor is merely a natural adjustment in the <br />population dynamics of a single species. <br />
The URL can be used to link to this page
Your browser does not support the video tag.