Collecting Baby Fish

Baby fish disperse widely from where they were hatched and it is difficult to strain these live baby fish out of natural bodies of water. Baby fish must be collected with special collecting devices. In most cases, biologists strain waters with fine-mesh nets to capture them. Collections with moving nets normally result in dead or dying specimens subsequently, light traps have been developed and are being used to collect them, so they may be studied alive. Also, slurp guns can be used to capture to capture live baby fish in surface waters or in shallow waters.

Figure 1) A ship towing double conical fine-mesh townets (Bongo nets), below, off the port side and a deep-running trawl off the stern.
Large ships tow the conical fine-mesh nets for some period of time, i. e. 30 minutes, at the depth of water that is selected. After 30 minutes or similar time, the nets are brought to the surface, the "cod ends"or plankton buckets are emptied into Mason jars or similar bottles and formalin added to the bottles to preserve the collection of young fish for examination under a microscope at some later date (Refs. 29 - 33).
 

 


Figure 2) Sky view of a boat, below, towing a single conical, fine-mesh townet.
LEFT: Illustration of single conical fine-mesh townet on the right side of the boat (or 2 nets, one on each side). The townet is let down into the water with the pulley and towed for some period of time, example 30 minutes, at the depth of water that is selected. After 30 minutes, the net is brought to the surface and the "plankton bucket" is emptied into a Mason jar or or similar bottle and formalin added to the bottle to preserve the collection of young fish (and plankton) for examination under a microscope at some later date.
RIGHT: Photo of townet on the left side of the boat being towed by a small motor boat. Compare the terms on the left illustration with the items in the photo on the right. (Ref. 8).

 
Figure 3) A Faber–type light trap, right, used to capture living baby fish.
Light traps are used after dark to capture living baby fish. Light traps are set out in the water and secured with ropes and anchors. The light is a flashlight bulb and the battery is 6 volts. The light trap is set out in the afternoon or early evening and a timer turns the light on at a selected time and then turns it off at a later time. The trap is picked up in the morning. The contents of the plankton bucket are emptied into a Mason jar or similar glass bottle and the specimens of baby fish captured are examined live later in the laboratory (Ref. 13). Light traps can be used to capture live specimens which can then be photographed (see examples: Australian Museum)

Figure 4) A hand-held minnow net, right, used to capture babies in shallow water.
Small hand-held nets can be used to capture baby fish in shallow water. These nets come in a variety of sizes. The baby fish can be seen in the shallow water and then captured with the net.

Figure 5) A slurp gun, right, used to capture babies in shallow water.
Slurp guns are valuable tools to capture live baby fish in surface waters or shallow water. Normally, slurp guns are used to collect live tropical fish in various situations. They are available in various lengths. One tries to get the snout as close to the live babies as possible, then pull the handle and suck the live babies into the body of the slurpgun.