Rapid embryonic development supports the early onset of gill functions in two coral reef damselfishes

Abstract

The gill is one of the most important organs for growth and survival of fishes. Early life stages in coral reef fishes often exhibit extreme physiological and demographic characteristics that are linked to well-established respiratory and ionoregulatory processes. However, gill development and function in coral reef fishes is not well understood. Therefore, we investigated gill morphology, oxygen uptake and ionoregulatory systems throughout embryogenesis in two coral reef damselfishes, Acanthochromis polyacanthus and Amphiprion melanopus (Pomacentridae). In both species, we found key gill structures to develop rapidly early in the embryonic phase. Ionoregulatory cells appear on gill filaments 3–4 days post-fertilization and increase in density, whilst disappearing or shrinking in cutaneous locations. Primary respiratory tissue (lamellae) appears 5–7 days post-fertilization, coinciding with a peak in oxygen uptake rates of the developing embryos. Oxygen uptake was unaffected by phenylhydrazine across all ages (pre-hatching), indicating that haemoglobin is not yet required for oxygen uptake. This suggests that gills have limited contribution to respiratory functions during embryonic development, at least until hatching. Rapid gill development in damselfishes, when compared with that in most previously investigated fishes, may reflect preparations for a high-performance, challenging lifestyle on tropical reefs, but may also make reef fishes more vulnerable to anthropogenic stressors.

Rapid physiological and transcriptomic changes associated with oxygen delivery in larval anemonefish suggest a role in adaptation to life on hypoxic coral reefs

“…Here, we found that, across their entire pelagic stage, larvae of cinnamon anemonefish have among the highest mass-specific oxygen uptake rates (i.e., both SMR and MMR) of any teleost fish species studied to date [ 9 ]. Specifically for anemonefishes and direct developing fishes that are well developed upon hatch [ 26 ], high SMR may be required to support oxygen demands of development and growth of complex tissues (e.g., eyes and brain) [ 26 – 28 ]. Additionally, anemonefish, specifically cinnamon anemonefish, are capable of swimming—a highly energetically demanding activity—immediately upon hatching, which will add to their metabolic demands.…”