Structural changes within fish schools correlate with declines in environmental oxygen. The changes may result from the responses of individual fish to the environmental consequences of group metabolism. Individual behaviors are adaptive to the school in that they tend to maintain stability between school members and their environment.

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The morphology of thefeedingapparatus in several genera of carcharhinid sharks (Carcharhinus, Rhizoprionodon, Hypoprion, Prionace, Galeocerdo and Negaprion) was studied in both fresh and preserved states. The actions of the cranial musculature were determined through electrical stimulation. The feeding behaviours of representatives of the genera Carcharhinus, Negaprion and Galeocerdo were studied under controlled conditions by direct observation as well as photographically. The cranial anatomy of carcharhinid sharks is characterized by a relatively reduced chondrocranium and a greatly hypertrophied musculature. The hyostylic jaw suspension serves to allow substantial cranial kinesis, particularly with respect to the upper jaw. Protraction of this skeletal element is accomplished in at least two ways, depending on the external and internal forces applied to the palatoquadrate cartilage. Under one set of conditions upper jaw protraction serves to allow precision when feeding on benthic organisms. Under quite different conditions upper jaw protraction allows the jaw to cut deeply through food items too large to be swallowed whole. The feeding mechanism found in these sharks, therefore, seems to be well adapted to deal with a wide variety of food types.