Early induced stress may result in the release of free haemoglobin into the skin mucus of teleostean fishes. If this were the case, it could be indicated quickly and simply by the colour change of a commercially available haemoglobin test strip. Preliminary tests on Mugil cephalus (grey mullet) encouraged more extensive investigations with Chanos chaaos (milkfish), Caranx ignobilis (papio), Albula vulpes (bonefish), and Chaetodon miliaris (butterfly fish). The results indicated that unstressed individuals of these species have no detectable haemoglobin in their skin mucus but, within 2-4 min, the pigment will appear in occult amounts if stress is applied. Additional studies confirmed that it was haemoglobin and no other possible contaminants in the mucus which caused the colour change of the test strip.The technique is simple and quick, and is itself harmless to the fish. It is of immediate potential value to fish culturists for the detection of early stress conditions. Efforts can then be made to lessen or remove the stress conditions before debility and possibly overt disease take over. A further application of the technique may be the identification of individuals genetically better able to resist disease.

Before and after application of severe, debilitating stress, automated chemical analysis was applied to the skin mucus and the serum of four subsistence fish species: Chanos chanos, MugiI cephalus, Sarotherodon macrochir and S. mossambicus. Certain tests were found to reflect the stress effects. Future use of these tests may be on an individual, less expensive basis. Greater use of mucus for analysis is suggested because it is more accessible and less traumatically obtained than blood.

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The detection of starvation is a major problem in fish husbandry. Too often the discovery of starving animals is not made until pathogenic organisms are about to overcome the weakened animals. A simple test, using a commercial plastic strip with a reagent area that changes colour in the presence of starvation-induced ketones, was applied to this problem in the mullet, Mugil cephalus. The strip identified ketones in the fish skin mucus, and demonstrated its value in detecting starvation in fishes.