Abstract

An experiment was conducted to evaluate the effectiveness and applicability of an external, non-invasive crayfish marking technique for population or production studies. A general-use oil-based permanent marker suitable for under water use was tested. The marker was applied on the wet carapace of red swamp crayfish (Procambarus clarkii), which were kept for 14 days in open- and closed-top cages in simulated crayfish production ponds. There was no significant degradation of the marks at the end of the 14 day experimental trial, except from natural fouling and dirt accumulation. Marked and non-marked crayfish averaged less than 4.5% and 7.0% mortality, respectively, suggesting that this marking technique is not directly harmful to crayfish. An observed 38% increase in crayfish “missing” from the open-top cages was probably attributable to predation and/or escapism. In closed-top cages, less than 3% of crayfish were missing, but it was inconclusive whether the bright markings contributed to predation in the open-top trial. This technique appears to be an excellent tool for conveniently marking crayfish for indoor or outdoor studies where moulting is not expected. It produces a durable mark, can be applied directly on wet or dry surfaces, dries in 25 – 35 seconds and there are several different colour and mark combinations possible. This technique also seems promising for marking other aquatic organisms.

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