Cardio-respiratory control during early development in the model animal zebrafish.

Independent of species, the cardiovascular system is the first functioning component of developing vertebrate embryos. One of the main hypotheses is the assumption that larval and juvenile stages of fish and amphibians are not just smaller versions of an adult phenotype. In this review, the cardiovascular and respiratory responses to environmental, genetic and epigenetic perturbations are discussed in detail to understand the relationships between cardiac and respiratory performance, haematopoiesis for embryonic or larval stages with special focus on the popular model animal, the zebrafish. Zebrafish are tiny animals which have many advantages as a model organism in analysis of the cardio-respiratory system. It obtains sufficient amounts of oxygen via bulk diffusion, in contrast to convection-dependent mammals. It is possible to study genetic mutants even with extreme defective phenotypes of the cardio-respiratory system in order to understand its developmental and physiological mechanisms. It has become apparent that the cardio-respiratory system and its control starts functioning very early during development, long before oxygen uptake becomes diffusion limited in zebrafish. Finally, recent improvements in imaging techniques for the use of fish models relevant for developmental physiology and biomedical research are discussed.