IONIC AND OSMOTIC REGULATION IN 3 SPECIES OF COTTUS (COTTIDAE, TELEOST)

1. 1. All three species of Cottus show some ability to regulate in foreigh media, although neither of the marine species will live in completely fresh, nor will the freshwater form withstand full-strength sea water. 2. 2. Total body sodium increases in all three species with increasing external salinity. 3. 3. C. morio loses sodium at a rate of 1·1 per cent total body sodium/hr in fresh water, but this rate only increases to 6·4 per cent/hr in 75% sea water, whereas the marine forms lose sodium at a rate of over 12 per cent body sodium/hr insea water. 4. 4. C. morio decreases its rate of water loss with increasing salinity, whereas that in the other speceis remains about the same at all external salinities. 5. 5. Both C. morio and C. bubalis increase the rate of drinking of the medium with increasing external salinity. 6. 6. The results are discussed in relation to the regulatory ability of other species from similar environments. © 1969.