The influence of saline concentration on the success of Calcein marking techniques for hatchery-produced Murray cod ('Maccullochella peelii')

Chemical marking is a useful technique to determine natal origin of fish and is increasingly used to determine the success of fish stocking programs. This study sought to optimise an osmotic-induction batch marking technique, using the calcium-binding chemical, Calcein, to enable future identification of hatchery-marked Murray cod (Maccullochella peelii). It was hypothesised that higher saline concentrations would create a more reliable bone mark but it was unknown whether saline exposure would influence fish survival. A laboratory trial was undertaken to determine the optimum saline concentration required to maximise survival of Murray cod and marking of bony body parts. Fish were exposed to a no salt control, a no Calcein control or one of three different saline concentration treatments then housed in either 60 L aquarium tanks or hatchery ponds and monitored for 43 days post marking. There was no significant difference in mortality rates among the three treatments under controlled aquarium conditions or among marked fish released into hatchery ponds. Whilst saline concentration did not influence fish survival, marking using concentrations less than seawater produced a detectable mark and reduced stress on Murray cod fingerlings. Mark intensity, however, was greater when fish were exposed to higher saline concentrations.