At the same time, there are usually severe constraints on adaptations to new food. As long as swimming continues to be important to a fish's lifestyle, any major change in body shape, such as a bulging visceral mass resulting from enlarging the stomach or lengthening the midgut, must extract a penalty in terms of increased effort needed for swimming. Feeding mechanisms must not interfere with the respiratory functions of the gills and vice versa. All in all, "packaged" so that any major change in the digestive system would call for major compromises in many other systems. Perhaps the best generalization is that teleost fish maintain an intimate relationship between the form and function of their gut and their food resource. In the final analysis, all of the other life processes continue to function only when sufficient materials and energy are obtained and assimilated via the gut.