Evaluation of three fluorochromes as in situ growth markers in Manila clam Ruditapes philippinarum

Marking technology is essential to evaluate the growth performance of shellfish species in aquaculture. Some fluorochromes have been widely used in shellfish growth studies, but their marking quality remains unresolved. In order to establish an effective marking technology in bivalves, three fluorochromes are used to evaluate the suitability of in situ growth markers in spats of commercially important bivalve, Manila clam Ruditapes philippinarum. Three different concentrations of calcein (CAL; 25 mg/L, 50 mg/L and 100 mg/L), alizarin red S (ARS; 5 mg/L, 10 mg/L and 20 mg/L) and oxytetracycline hydrochloride (OTC; 250 mg/L, 500 mg/L and 750 mg/L) were used to examine their potential effects on marker quality, growth and survival of spats. In general, marking quality scores for the three fluorochromes have a positive correlation with their increased concentrations. CAL (50-100 mg/L) and ARS (10-20 mg/L) have produced healthy spats with a bright and clear fluorescent shell mark after the recovery culture for 69 days. In contrast, OTC appears to have the weak staining signals at all concentrations. The growth and survival rates affected by fluorochrome immersion are negligible at all concentrations. The present findings indicate that in situ CAL and ARS marking of spats with moderate concentrations are non-invasive and effective method for growth studies in clams. The suitability of CAL and ARS as in situ growth markers in clams will provide new marking techniques to distinguish cohorts or families in aquaculture.