Quality of giant clam (Tridacna derasa) juveniles as non–target organisms after exposure to clove oil in concentrations suitable for anaesthetising ornamental fish

Abstract

The use of clove oil as an alternative to cyanide has proven effective for catching several types of ornamental fish on coral reefs. However, it is very important to evaluate the post-exposure condition of non-target organisms in coral reef ecosystems where ornamental fishing occurs, such as juvenile tridacnid clams. The aim of this study was to analyse the condition of juvenile clams (Tridacna derasa juveniles, size class 3-4 cm shell width) after exposure to clove oil at the concentrations found effective for ornamental fish capture. A factorial experimental design was used with 7 clove oil concentrations (control, 20 ppm, 30 ppm, 40 ppm, 50 ppm, 60 ppm, 70 ppm) and 5 post-exposure times (1,5,9,13 and 17 days) with 3 replicates per treatment. The juvenile clams were acclimatized for a week before being exposed to clove oil for 5 minutes, then transferred to a recovery aquarium for 60 seconds before being placed in holding aquaria. The density and mitotic index of the zooxanthellae in the clam mantles were measured for each treatment and time. There was no significant difference (p> 0.05) between control clams and those exposed to clove oil with concentrations from 20 - 70 ppm in either the density or the mitotic index of zooxanthellae present. These results indicate that juveniles of the clam Tridacna derasa did not experience a significant decline in quality (condition) after a short exposure to clove oil, such as might typically occur if clove oil was used in ornamental fishing on coral reefs.