A second look at the stomach - a fishy perspective.

Despite the established evolutionary importance of stomach acidification in vertebrates, the exact contribution of this process to overall protein digestion, nutrient absorption, growth, energy metabolism and development has not been fully elucidated and is oftentimes subject to extensive scientific debate. This Commentary sets out to frame the current state of our understanding, highlighting unresolved issues and proposing where experimental approaches can be applied to address these questions. Furthermore, we explore in depth the tantalizing evolutionary and physiological puzzle of repeated loss of gastric function in fishes. In this way, we hope to help clarify the role of the gastric proton pump and stomach acidification in digestion, metabolism and growth in vertebrates.