Ocean acidification is predicted to affect marine ecosystems in many ways, including modification of fish behaviour. Previous studies have identified effects of CO 2 -enriched conditions on the sensory behaviour of fishes, including the loss of natural responses to odours resulting in ecologically deleterious decisions. Many fishes also rely on hearing for orientation, habitat selection, predator avoidance and communication. We used an auditory choice chamber to study the influence of CO 2 -enriched conditions on directional responses of juvenile clownfish ( Amphiprion percula ) to daytime reef noise. Rearing and test conditions were based on Intergovernmental Panel on Climate Change predictions for the twenty-first century: current-day ambient, 600, 700 and 900 µatm p CO 2 . Juveniles from ambient CO 2 -conditions significantly avoided the reef noise, as expected, but this behaviour was absent in juveniles from CO 2 -enriched conditions. This study provides, to our knowledge, the first evidence that ocean acidification affects the auditory response of fishes, with potentially detrimental impacts on early survival.

To determine how each new generation of the sea urchin cardinalfish Siphamia versicolor acquires the symbiotic luminous bacterium Photobacterium mandapamensis, and when in its development the S. versicolor initiates the symbiosis, procedures were established for rearing S. versicolor larvae in an aposymbiotic state. Under the conditions provided, larvae survived and developed for 28 days after their release from the mouths of males. Notochord flexion began at 8 days post release (dpr). By 28 dpr, squamation was evident and the caudal complex was complete. The light organ remained free of bacteria but increased in size and complexity during development of the larvae. Thus, aposymbiotic larvae of the fish can survive and develop for extended periods, major components of the luminescence system develop in the absence of the bacteria and the bacteria are not acquired directly from a parent, via the egg or during mouth brooding. Presentation of the symbiotic bacteria to aposymbiotic larvae at 8-10 dpr, but not earlier, led to initiation of the symbiosis. Upon colonization of the light organ, the bacterial population increased rapidly and cells forming the light-organ chambers exhibited a differentiated appearance. Therefore, the light organ apparently first becomes receptive to colonization after 1 week post-release development, the symbiosis is initiated by bacteria acquired from the environment and bacterial colonization induces morphological changes in the nascent light organ. The abilities to culture larvae of S. versicolor for extended periods and to initiate the symbiosis in aposymbiotic larvae are key steps in establishing the experimental tractability of this highly specific vertebrate and microbe mutualism.

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Coral reef fishes exhibit a diversity of hermaphroditic strategies and comparisons among species with different ecological characteristics will help identify the underlying basis of this complexity. We used manipulative experiments to test the potential for bi-directional sex change in three species of Pseudochromis (Pseudochromidae): P. flavivertex, P. aldabraensis and P. cyanotaenia. The first two species are sexually monochromatic, whereas, P. cyanotaenia is sexually dichromatic. For each species, where two functional females were kept together, one individual in the pair changed sex to male. Where two functional males were kept together, one individual in the pair changed sex to female. In all three species, functional sex change from male to female (52-93 days) took longer than sex change from female to male (18-56 days). In the sexually dichromatic species, P. cyanotaenia, colour change accompanied adult sex change. Females that changed sex to male took on the bright colouration of males and males that changed sex to female took on the drab colouration of females. These results indicate that bi-directional sex change is probably widespread in the family Pseudochromidae and cannot be predicted by the presence or absence of secondary sexual characteristics.