in to a large aquarium, preferably from a natural 

 source, and is circulated by means of a small pump. 

 A pump with stainless steel and plastic fittings is 

 needed, and plastic tubing should be used to avoid 

 possible toxic effects from metal surfaces. The 

 current can be adjusted by the speed of the pump, 

 and microhabitats are created by stones and other 

 bottom materials from the natural habitat or by plastic 

 baffles placed at strategic points. 



Food is of course an important consideration in 

 rearing aquatic insects. The readily available aquar- 

 ium plants may be used for plant feeders and will 

 contribute to the conditioning of the water or may 

 even result in a "balanced aquarium." Predatory 

 insects must be supplied with particular kinds of 

 living food. This can become a major problem but 

 here again the aquatic entomologist is indebted to 

 suppliers of equipment and materials for home aquaria. 

 Brine shrimp may be purchased at small cost or may 

 be reared from eggs that are obtainable commercially. 

 Other live food material that can be maintained in 

 culture includes mosquito larvae (especially Aedes 

 aegypti in areas where it occurs naturally), house 

 flies, Drosophila flies, meal worms, and water fleas 

 (Daphnia). Techniques for rearing these are relatively 

 simple (see Needham, et al., 1937). On a more limited 

 scale, nonpredaceous insects such as mosquito larvae 

 and some mayfly nymphs can be collected in the field 

 and added to the aquarium as needed for food. 



The running water habitat poses special problems 

 i in food supply. Most stream insects are grazers on 

 11 the periphyton that coats rocks and other objects in 

 the water. Small rocks should be moved from the 

 ). natural habitat to supply this type of food and fresh 

 f periphyton-covered surfaces may have to be supplied 

 at intervals. 



FISH COLLECTING AND EXAMINATION 



OF STOMACH CONTENTS 



When conducting an aquatic survey, it is desirable 

 to know what the fish are eating and to correlate the 

 percentage of the various insects in the stomachs 

 of the fish with the percentage in the habitat (Hess 

 and Swartz, 1941). Frequently one insect species 

 may be in great abundance, but the fish stomachs 

 reveal that some other species is the dominant one 

 selected by the fish. To obtain such information, 

 fish are collected and the stomachs removed. As 

 soon as possible after collecting, the stomachs are 

 placed in vials of alcohol or 5 per cent formalin. Each 

 specimen should be labeled, giving the species of 

 fish, locality, date, collector, and any other pertinent 

 information. The stomachs are usually examined later 

 in the laboratory, where they can be opened with care 

 and where the contents can be sorted under a dissect- 

 ing microscope. Identification is difficult and some- 

 times impossible because many of the specimens are 

 represented only by a few fragments. The work is 

 considerably easier when an adequate collection 

 has been made of the insects in the environment. 

 This permits a correlation to be made between the 

 fragments in the stomachs and the intact specimens 

 collected in the field. 



63 

 Latfin: Introduction 



Fish collecting methods. — One of the commonest 

 methods of "collecting" fish is, of course, In hook 

 and line. Students of fish foods sometimes find this 

 a convenient way to combine business and pleasure. 

 Other methods which are more likely to produce 

 quantities of fish for scientific study include seining, 

 poisoning, shocking, and draining. These mass col- 

 lecting methods are illegal for game fish in most 

 states but special permits may be obtained for scien- 

 tific studies. 



Seining is a common method of collecting fish for 

 scientific purposes. The nets used vary in size and 

 mesh, depending on the type of fish being collected. 

 Gill nets are used when it is possible to remain in 

 an area for several hours or ovornight. They are 

 designed to allow the fish to pass through the mesh 

 as far as the gills. Once in the net, the fish tries to 

 back out and becomes entangled. A net of several 

 sized meshes is used to ensure catching most types 

 of fish present. Fish caught in gill nets are less 

 satisfactory than those collected by other methods 

 because the stomach contents are more completely 

 digested and hence more difficult to identify. The 

 fish poison, rotenone, is useful for collecting in 

 small ponds, slow streams, and protected bays in 

 larger bodies of water. The poison constricts the 

 capillaries in the gills, preventing the flow of blood 

 in this region and thus greatly reducing the exchange 

 of oxygen and carbon dioxide. This causes the fish 

 to rise to the surface to get more air where they are 

 collected by means of a hand net. The electric shocker 

 is used to collect and tag fish in streams and small 

 ponds. A battery or generator supplies the power. 

 Shocking temporarily stuns the fish, permitting them 

 to be collected. The pump and drain method, when 

 feasible, is perhaps the best method of determining 

 the exact number of fish in a given area of stream. 

 A section of the stream is blocked off and the water 

 diverted around it. The section to be sampled is then 

 pumped out and fish are collected, counted, weighed, 

 and utilized for other scientific purposes, after which 

 they may be returned to the restored stream bed. 

 Smaller fish, usually overlooked or missed by other 

 methods, are taken in great numbers by pumping and 

 draining. Small ponds can also be pumped dry. 



MEASUREMENT OF PHYSICAL AND 

 CHEMICAL FACTORS 



In addition to biological collections, it is often neces- 

 sary to measure and record certain physical and 

 chemical features of the aquatic environment. The 

 following is a brief summary of the equipment and 

 techniques used to obtain the minimum data that 

 should be taken on any survey. This section is taken 

 largely from Davis (1938). 



Physical Factors 



Temperature. — A simple laboratory thermometer, 

 properly calibrated, will serve to record air and water 

 surface temperatures. If a series of temperatures is 

 required from various depths in a pond or lake, then 



