Homing is not for everyone: displaced cardinalfish find a new place to live.

It was tested whether the pajama cardinalfish Sphaeramia nematoptera (Apogonidae) could home by displacing individuals up to 250 m within and among isolated reefs. Contrary to expectations, only two of 37 (5·4%) displaced S. nematoptera returned home and another 16 (43·2%) were found to have joined other social groups and did not home after 26 months of observations; while over the same period, 94% of control S. nematoptera remained associated with home corals, demonstrating strong site attachment. Hence, while this species has the potential to return home, being able to do so may not be as critical as previously assumed.

Alterations in gill structure in tropical reef fishes as a result of elevated temperatures.

Tropical regions are expected to be some of the most affected by rising sea surface temperatures (SSTs) because seasonal temperature variations are minimal. As temperatures rise, less oxygen dissolves in water, but metabolic requirements of fish and thus, the demand for effective oxygen uptake, increase. Gill remodelling is an acclimation strategy well documented in freshwater cyprinids experiencing large seasonal variations in temperature and oxygen as well as an amphibious killifish upon air exposure. However, no study has investigated whether tropical reef fishes remodel their gills to allow for increased oxygen demands at elevated temperatures. We tested for gill remodelling in five coral reef species (Acanthochromis polyacanthus, Chromis atripectoralis, Pomacentrus moluccensis, Dascyllus melanurus and Cheilodipterus quinquelineatus) from populations in northern Papua New Guinea (2° 35.765' S; 150° 46.193' E). Fishes were acclimated for 12-14 days to 29 and 31°C (representing their seasonal range) and 33 and 34°C to account for end-of-century predicted temperatures. We measured lamellar perimeter, cross-sectional area, base thickness, and length for five filaments on the 2nd gill arches and qualitatively assessed 3rd gill arches via scanning electron microscopy (SEM). All species exhibited significant differences in the quantitative measurements made on the lamellae, but no consistent trends with temperature were observed. SEM only revealed alterations in gill morphology in P. moluccensis. The overall lack of changes in gill morphology with increasing temperature suggests that these near-equatorial reef fishes may fail to maintain adequate O2 uptake under future climate scenarios unless other adaptive mechanisms are employed.