MOTE MARINE LABORATORY
Table of Contents
|Vent vs. Non-Vent|
|How to Vent Your Fish|
|Comparison of Fish Vented vs. Non-Vented|
Many fish have swimbladders or gas bladders. As a general rule, fish with spiny fin rays have closed swimbladders and fish with soft fin rays have open swimbladders. The closed bladder acts like a
balloon that has been tied off with the gas trapped inside. The open bladder acts like an untied balloon and gas is free to move in and out.
You may have noticed that some fish caught at depths have their intestines coming out of their anus, eyes bulging out of their heads and stomachs protruding out of their mouths. This is because these fish have closed gas bladders that have expanded and ruptured and the gasses from the bladder have displaced the internal organs as they were brought rapidly to the surface.
The pressure exerted on their bodies decreases during ascent, allowing the gases to expand in their bodies. If the fish is kept, this is not a problem, but if it is thrown back, it helplessly floats on the surface, exposed to the elements and is easy prey for sea birds and predatory fish.
An alternative to throwing the bloated fish back is to purge the air from it's body before release. This can be accomplished by using a hollow puncturing device like a syringe or a sharpened basketball needle. Proper purging of the air will allow the fish to swim back to the bottom and find a suitable hiding place. It is assumed that this purging increases it's chances of survival.
This study is being conducted to investigate that assumption. Mote Marine Lab and RSMAS are conducting this study with funding by FL Sea Grant.
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Species Involved: Red Grouper, Epinephelus morio, Gag, Mycteroperca microlepis, Red Snapper, Lutjanus campechanus, Vermilion Snapper, Rhomboplites aurorubens, Mutton
Snapper, Lutjanus analis and Mangrove Snapper, Lutjanus griseus.
To differentiate possible effects of deflation (venting) from those due to depth of capture, fish were tagged and released in equal numbers with deflated versus non-deflated abdomens in discrete depth
categories: 0-4, 41-70, 71-100, 101-200 and +201.
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The total number as of October 16, 2002, of tagged, recaptured and vented fish vs. the number non-vented fish for each species is shown in the provided table. The goal in providing this table is to show which categories need to be filled. For example, there are smaller numbers in all the +201 depth category. Also, there are more vented fish than non-vented fish at this depth.
The purpose of this study is to determine the potential survival of vented versus non-vented fish, so equal numbers of these fish must be treated to determine if a difference in survival rates exists. Obviously, it is necessary to vent fish that are caught in the +201 ft. depth category but for the purpose of this study, a number of fish need to be returned unvented and recorded for the control group.
In the 0-4-ft. depth category, there are few vented fish. Although it may not be necessary to vent fish at this depth, these vented fish will be used to determine if venting causes infections and/or physical harm to the fish. Please vent more fish in this depth category.
As shown in the following table, more gag, red grouper, red snapper, vermilion snapper, mangrove snapper and mutton snapper need to be
tagged for this project. Please use these tables as a guide in determining whether or not to vent your catch. For our statistics to be valid, we must have equal numbers (as close as possible) of
treated fish vs. non-treated fish to compare.
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Comparison of Fish Vented Vs. Non-Vented at Various Depths
From October 1990 through October 16, 2002
|Gag Grouper||Tagged Vented||Not Vented||Recap. Vented||Not Vented||Red Grouper||Tagged Vented||Not Vented||Recap. Vented||Not Vented|
|0-40 ft||159||1333||10||74||0-40 ft||257||679||50||117|
|41-70 ft||925||1351||102||134||41-70 ft||4127||3196||197||252|
|71-100 ft||448||376||55||44||71-100 ft||1484||833||121||109|
|101-200 ft||116||36||20||6||101-200 ft||816||195||69||12|
|200+ ft||18||4||0||0||200+ ft||35||3||1||0|
|Red Snapper||Tagged Vented||Not Vented||Recap. Vented||Not Vented||Mangrove Snapper||Tagged Vented||Not Vented||Recap. Vented||Not Vented|
|0-40 ft||1||6||0||0||0-40 ft||780||445||49||15|
|41-70 ft||1004||117||95||14||41-70 ft||5||2||0||0|
|71-100 ft||1879||426||117||48||71-100 ft||7||7||0||0|
|101-200 ft||931||96||57||9||101-200 ft||2||0||0||0|
|200+ ft||2||0||0||0||200+ ft||0||0||0||0|
|Vermilion Snapper||Tagged Vented||Not Vented||Recap. Vented||Not Vented||Mutton Snapper||Tagged Vented||Not Vented||Recap. Vented||Not Vented|
|0-40 ft||13||5||0||0||0-40 ft||4||1||2||0|
|41-70 ft||182||22||1||0||41-70 ft||2||1||1||0|
|71-100 ft||569||80||4||0||71-100 ft||2||0||0||0|
|101-200 ft||94||21||2||0||101-200 ft||4||1||0||0|
|200+ ft||1||0||0||0||200+ ft||0||0||0||0|
Last Updated: June 15, 2004
Web Site Design: Don Marshall