Why do more predatory salmonid fishes tend to have more pyloric caeca?

Within the family Salmonidae, there is a noted tendency for more predatory species to possess a higher number of pyloric ceca. These fingerlike appendages, which open off the intestine just posterior to the stomach, function by secreting digestive enzymes and providing additional surface area for digestion.1

While this correlation exists among salmonids, it is important to note that this relationship between diet and pyloric caecal development does not apply broadly to all fishes. For instance, the highly predatory pikes of the genus Esox lack these structures entirely, while the algae-eating ayu (Plecoglossus altivelis) possesses an exceptionally high number of ceca, sometimes reaching 400 or more. Thus, while increased caecal development supports the digestive needs of certain predatory salmonids, it is not a universal physiological requirement for predatory behavior across all fish species.1