Kmgsford and Hughes Growth, mortality, and size of Acanthochromis polyacanthus 



563 



Figure 1 



Map of the nine reefs on the central Great Barrier Reef where Acanthochromis poly- 

 acanthus were collected. Distance strata from the mainland (i.e. inner-, mid- and 

 outer-shelf distances I are also indicated. 



overnight. One otolith from each fish was then imbed- 

 ded in Struers Epofix resin that was allowed to harden 

 overnight in a drying oven at 60°C. A thin (250-300 jmi) 

 transverse section perpendicular to the long axis of the 

 otolith was then taken through the core (primordium) 

 of the otolith with a Buehler low-speed saw with two 

 spaced diamond blades. This section was polished by 

 hand with 9-,«m lapping film to remove saw blade marks, 

 thereby making the internal structure of the otolith 

 more clearly visible. The polished section was then fixed 

 to a labelled glass microscope slide with Crystal bond 

 thermoplastic glue. 



Analysis of growth increments 



The opaque zones visible in the internal structure of 

 the otolith were counted along a radius from the pri- 

 mordium to the outer edge of the largest sagittal lobe of 

 the otolith with a compound microscope (Leica DMLB) 

 and white incident light source. Alternating translucent 

 and opaque increments were interpreted as annuli. Sec- 

 tions were coded and examined in random order and 

 the opaque increments counted on two occasions by the 



same observer (JMH) separated by four weeks. Counts 

 of annuli were compared between these two occasions 

 in order to assess the confidence that could be placed 

 in the interpretation of otolith structure. If increment 

 counts differed by more than two between counting occa- 

 sions, then the otoliths were re-examined. If, following 

 a third reading, agreement between the third and one 

 of the two other counts was not reached (all matching 

 counts were used in analyses), then the otolith was not 

 included in the analysis; 4.6% of otoliths were rejected 

 on this basis (n=715 fish). 



Validation of growth increments 



The periodicity of growth increment formation was vali- 

 dated by marking a group offish (of various sizes) reared 

 in captivity with the antibiotic tetracycline hydrochlo- 

 ride (Sigma-Aldrich, Ballerup, Denmark). Small (known 

 to be 0+ fish) and large fish were chosen to determine 

 if annuli are formed early and late in life. Fish were 

 held at the MARFU Aquarium Facility, James Cook 

 University. For the duration of the experiment, the fish 

 were held in several 70-500 L aquaria at this facility. 



