Introduction

Because of the Relative Ease with which pond organisms can be reared under laboratory conditions, the rearing of stream-dwelling organisms tends to be neglected. This article provides brief descriptions and a literature list of techniques used to rear stream organisms in the laboratory.

One difficulty in setting up an artificial stream is the transfer of stream fauna from their natural habitat to the laboratory. The death of fauna during transfer is caused usually by an inadequate oxygen supply and/or rapid increases in temperature.

The oxygen supply can be maintained at an adequate level if a small volume of water with a large surface area is continually agitated. Rapid agitation, however, may cause damage to delicate insect larvae. If large volumes of water are necessary for transport of fauna, an adequate supply of oxygen can be maintained by using an air bubbler. It is possible to construct a simple air bubbler from a large plastic funnel, by attaching a bubbler tube to the neck and directing the open end of the funnel into the windstream created by the vehicular transport (Fig. A.). This method of aeration, however, rapidly raises the water to air temperature.

Temperature Control

Temperature may be controlled by using large mouthed “Thermos” flasks during transport. Large volumes of material can be transported with good temperature control by using expanded polystyrene “Chillybins.”

Food

Growths of algae for browsing insect larvae can be obtained by seeding the artificial stream with natural stream water. However, some species of Ephemeroptera larvae eat considerable amounts of algae and can easily eat all available food if large numbers of larvae are placed in the stream. In artificial streams where filtered tap water is used, food must be added for filter feeders. Yeast suspension has been used successfully by D. M. Woods (pers. comm.) to feed Simuliidae larvae.

Toxic Substances

Some town water supplies are highly toxic to many stream animals because of such additions and impurities as hypochlorite and heavy metal ions. Copper retaining screens were found to be highly toxic to Simuliidae larvae by Hartley (1955), who also mentions that other workers have experienced difficulties with contamination when the water supply was in contact with copper. D. M. Woods (pers. comm.) uses activated charcoal filters successfully to remove both hypochlorite and heavy metal ions. Because of possible contamination no metal should be in contact with the water contained in artificial streams.

Techniques

Techniques for rearing stream organisms in the laboratory vary considerably in the way the currents are produced, but can be placed into two broad categories:—(1) Open Systems and (2) Closed Systems.

(1) Open Systems: These are the simplest types of artificial streams, but depend on the abundance and purity of local water supply. The simplest type of Open System stream splashes tap water over rocks and stones which have been brought to the laboratory with the organisms still attached. B. Mannheims (pers. comm.) has used this arrangement to rear Blepharoceridae larvae to adults. A similar arrangement uses a stream of water directed into jars or Petri dishes and allows the water to overflow to waste (Fig. B). Hartley (1955) and Carlsson (1962) used jars and page 67

Figure A: A simple portable bubbler. FIGURES B, C & D.: Open System streams. Figures E. & F.: Closed System streams using rotating current.

page 68 Petri dishes respectively to rear Simuliidae larvae. Hartley says that if the vessels are not raised off the bench the larvae will eventually migrate down onto the bench. Tonnoir (1923) produced a cascade of water by arranging porcelain evaporating dishes on an inclined plane, so that the water poured from one to the other. This arrangement was used to rear Blepharoceridae larvae (Fig. C.). To prevent larvae from escaping, gauze was attached over the pouring lips of the dishes. This arrangement is ideal for keeping species separated and lends itself to considerable modification. A trough with a stair-like base has been used by Thomas (1946) and by Dalmat (1955) to rear Simuliidae larvae.

Water flowing rapidly down plastic troughs has been used by D. M. Woods to rear Simuliidae larvae, similarly concrete channels with glass observation ports have been used by Dorier and Vaillant (1954) to study the effect of current on numerous aquatic invertebrates. Large (approximately lin. internal bore) plastic tubing with the water flowing through has been used by Carlsson to rear Simuliidae. and by the writer to rear Chironomidae, Blepharoceridae and Simuliidae.

A glass aquarium with a jet of water directed against one side, below the water line, provides a good basis for a general stream aquarium (Fig. D.). The depth of water, current and substrate can be varied with ease. Both Tonnoir and Carlsson used similar methods to rear Blepharoceridae and Simuliidae and the writer has reared Chironomidae, Blepharoceridae, Ephemeroptera and Trichoptera using this arrangement.

(2) Closed Systems: These types of artificial streams allow greater control of temperature, mineral nutrients, food and hydrogen ion concentration than Open System streams. Unfortunately, nearly all of the numerous methods of producing currents in these streams are completely dependent on electrical power.

By using a stirrer to produce a circular current in a jar (Fig. E.), Philipson (1953) was able to study the feeding habits of Trichoptera larvae. However, to investigate the effects of water flow and oxygen concentrations on 6 species of Trichoptera larvae, Philipson (1954) used jars with rotating glass stoppers which were lubricated with paraffin oil, the stirrers being attached to the inside centre of the stoppers. Whitford and Schumacher (1961) used a modified magnetic stirrer to study the effect of current on algal metabolism. In a similar method immobile plates were suspended within a rotating jar of water (Fig. F.). By oscillating jars in an horizontal plane a gentle circular current can be created. Freeden (1959) used these last two methods to rear certain species of Simuliidae larvae.

Air bubbled through water will produce sufficient turbulence or current to keep most stream organisms alive. However, Freeden reports that apparently the upper velocity limit of the water current page 69

Figures G, H. & I.: Closed System streams using compressed air. Figure J.: Closed System stream using recirculation.

page 70 produced by this method is 1.4 ft. per sec., this being inadequate for certain species of organisms. This method also rapidly raises the water to air temperature. Air bubbled up through an open tube (Fig. G.), or up an inclined glass plane (Fig. H.), suspended within a large volume of water forms the basis of the methods used by Puri (1925), Smart (1934), Makerras and Makerras (1948) and Davies and Smith (1958) for rearing Simuliidae larvae. Doby, David and Rault (1959) have reviewed these and other methods for rearing Simuliidae. Simuliidae larvae have been reared in 10 ml. test tubes with air diffusers by D. M. Woods (pers. comm.) (Fig. I.). This is a useful method when the volume of compressed air is limited.

Recirculating apparatus usually consists of pump, a straight trough and a reservoir. The water is pumped from the reservoir either directly into the trough or firstly into an upper head-tank, and thence into the trough. Troughs in artificial streams of this type have been constructed from wood, earthenware, asbestos-fibre and perspex; self-priming centrifugal pumps appear to have been used rather than other types of pumps. Refrigeration units for temperature control are usually placed in the reservoir. Using apparatus of this type, Zahar (1951), Wright (1957) and Hall and Harrard (1963) have reared Simuliidae; Moore (1964), freshwater snails; Whitford, Dillard and Schumacher (1964), lotic organisms, and Lauff and Cummins (1964), have studied lotic ecology.

Apparatus based on the recirculation principle has been used to study the metabolism of running water organisms. In these cases the stream was completely enclosed and airtight. Odum and Hoskins (1957) have studied algal metabolism, Gaufin and Gaufin (1961) the effect of oxygen concentration on Trichoptera larvae, and Brett (1965) the metabolism of Canadian salmon. Sudia (1951) used an oval galvanised iron tank to study the effects of water flow on mosquito larvae. The current was produced by nozzles directing the water around the trough.

The writer has constructed an artificial stream of the circulation type incorporating many of the ideas from other workers (Fig. J.). The stream has been designed to provide a flexible piece of apparatus for use in as many fields of research as possible.

A fibre-glass centrifugal pump capable of delivering 700 gallons of water an hour, though not running to full capacity, is powered by a ⅓ h.p. intermittent-running electric motor. The water is pumped into a head-tank and is maintained at a set level by an off/on float switch which controls the motor and pump. A ball-cock valve which is connected to the tap-water supply becomes activated if the water in the head tank falls below a minimum level. This ensures a water flow in case of power failures or breakdown of the pump or motor. From the head-tank the water flows down large-bore plastic tubes into the stream portion of the apparatus, page 71 a straight perspex trough, 3 ft. by 6 in. by 6 in. Wells at each end of the trough help to break the flow of incoming water and facilitate the removal or addition of organisms and substrate. A nylon gauze barrier at the outlet of the trough retains the organisms. Small ridges on the base of the trough retain the substrate, which in this case consists of small stones. The trough is roofed with perspex plates. Above the trough is suspended a daylight-type fluorescent tube and a time switch to provide approximately daylight conditions. The light from the fluorescent tube is sufficient to allow growth of algae and Hepaticae. From the trough the water flows through a filter of activated charcoal and then into the reservoir. Heating and refrigeration units for temperature control are suspended in the reservoir. The total volume of water held in the complete apparatus is approximately 60 gallons.

This stream has performed without major trouble for approximately twelve months. Stream organisms reared successfully so far are algae, Hepaticae, Turbellaria, Gastropodia, Ephemeroptera, Plecoptera. Neuroptera, Trichoptera, Chironomidae, Blepharoceridae and Simuliidae. The stream has also been used to study the effects of current on various species of N.Z. Galaxidae fish.