O-2 replenishment to fish nests: males adjust brood care to ambient conditions and brood development

Parental care through nest defense and maintenance enhances offspring success. In nature, obligate anemone-dwelling fishes and their nests of benthic eggs are protected against most predators by their host anemone; thus, parental care generally consists of nest tending through fanning and mouthing. Tending in fishes is believed to oxygenate the eggs; however, a real-time link between fanning and oxygenation is tenuous. This study investigated whether tending modified the oxygen microenvironment of the embryos and, subsequently, whether tending was modified according to ambient dissolved oxygen (DO), increasing metabolic demands of developing embryos, and water temperature. There was a time lag of approximately 1 s between tending and increases in the amount of oxygen within the nest, demonstrating that DO is directly affected by parental tending. While there was evidence of biparental care, males invested more time tending embryos (40% initially) than did females (20-30%), and male investment increased to 70% as embryo development progressed and embryonic metabolic demands increased. Additionally, male fish adjusted tending effort on a diel cycle as ambient DO fluctuated: time spent tending was lowest between 1000 and 1400 h (35%), when ambient DO was highest, and increased throughout the day, reaching a peak of 70% between 2200 and 0200 h, when ambient DO was lowest. Increased water temperature reduced the number of tending bouts per minute throughout the day but did not influence any other aspect of tending behavior. These results suggest that fish adjust tending behavior coincident to changing conditions in the nest, both on a daily basis and throughout development of the embryos. © International Society for Behavioral Ecology 2004; all rights reserved.