Theses and Dissertations

Title: Control of snails by the redear (shellcracker) sunfish

Name: Carothers, John Lee

Degree: MS

Chair: Dr. Ray Allison

Resides: FAA Library

University: Auburn

Location: Auburn, Alabama

Date: 1961

Pages: 39

Keywords: Redear,Shellcracker,Lepomis microlophus,Snails,Feeding,Digestion.


Snails are the intermediate hosts of many trematode parasites of man, fish and other animals. The control of snail populations is therefore of great importance. Biological control of two species of native pond snails, Physa sp. and Lymnaea sp., was attempted using the redear sunfish, Lepomis microlophus (Gunther). The research reported herein was conducted at Auburn University, Auburn, Alabama, from September, 1959, to December, 1960. The feeding habits of redears were studied under varied conditions in aquaria. Rates of feeding were usually based on the body weight of the individual fish, with each fish being fed daily over a 5- to 7-day period. Snails alone were offered to redears at rates up to 8 per cent of their body weight daily for 7 days. With few exceptions all snails were eaten. Snail consumption remained high even when midge larvae and dragonfly numphs were fed in addition to snails. When snails and midge larvae were fed at rates of 2 and 6 per cent respectively, redears ate 73.3 per cent of the snails offered. When the feeding rate of snails was doubled, fish ate 70 per cent of the snails offered. Snails comprised 39.1 per cent of the food eaten by redears when 16.6 per cent of the available food consisted of snails and 83.4 per cent consisted of dragonfly numphs. When 28.6 per cent of the food given consisted of snails, they made up 48.6 per cent of the total food eaten. The stomach contents of fish fed equal amounts of snails, dragonfly numphs, and midge larvae in aquaria were analyzed. Snails comprised 9.1 per cent of the total amount eaten by these fish. A series of concrete ponds containing snails was stocked with redears, or bluegills, Lepomis macrochirus Rafinesque, or received no fish. Although the survival of adult snails stocked in ponds was low, only those stocked with redears were devoid of adult snails. Both species of fish greatly reduced or eliminated snails from plastic pools not containing aquatic vegetation: however, their control by bluegills was believed to be the result of insufficient food. Snails on the sides of plastic pools containing soil and 6 species of aquatic plants were reduced 80.6 to 98.9 per cent within 1 day following the introduction of redear sunfish. The stomach contents of 63 redear sunfish taken from natural waters sparsely populated with snails were analyzed. Snails comprised 8.5 per cent of the contents of the 49 stomachs containing food. A study was made of the mechanics of the redear's feeding on and digestion of snails. Various sizes of snails were fed to fish that were killed 1 or 3 hours later, and their stomach contents analyzed. The amount of shell ingested was inversely proportional to the size of the snail. The foot of the snail was most resistant to the digestive process and retained its identity upon entry into the intestine.

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