The Reactions of Fish to Water of Low Oxygen Concentration

Abstract

1. This paper presents the results of about 100 experiments to test the reactions of small fish to water of low oxygen concentration, using an apparatus similar to that previously employed by the writer to study the reactions of fish to toxic solutions. 2. At 13°C. the stickleback (Gasterosteus aculeatus) has no immediate appreciation of water of low oxygen concentration and will swim into it with no hesitation. If the fish remains in the poorly oxygenated water respiratory distress develops, accompanied by uneasiness and random movement. When this random movement takes the animal back into the well-oxygenated water the stimulus to swimming vanishes, the fish stops moving and quickly recovers. Over a wide concentration range at 13°C. the reaction takes 1-3 min. At 3°C. the reaction is very slow, taking 5-6 min. even when the water contains only 0.3 mg./l. of oxygen. At 20°C. and oxygen concentrations below 2 mg./l. the response is very prompt, respiratory distress developing so quickly that the fish usually will not swim into the poorly oxygenated water, but turns away from it or swims backwards; it may make repeated attempts to enter the low-oxygen zone, retreating each time as if violently irritated. 3. Experiments with minnows (Phoxinus phoxinus) and trout fry (Salmo trutta) gave generally similar results. Here again the essential factor appears to be the speed with which dyspnoea develops.