Control of the trematode Bolbophorus confusus in channel catfish Ictaluruspunctatus ponds using salinity manipulation and polyculture with black carp Mylopharyngodon piceus

This study evaluated the use of black carp Mylopharyngodon piceus and salin ity manipulation for controlling the infection of channel catfish Ictalurus punctatus by a digenetic trematode (tentatively identified as Bolbophorus confusus). Control methods focussed mainly on the eradication of the interm ediate snail host, the marsh rams-horn Planorbella trivolvis (previously re ferred to as Helisoma trivolvis), and were evaluated in laboratory tests an d field experiments at a commercial catfish culture facility in southern Lo uisiana that was seriously impacted by the trematode, introduction of finge rling black carp into catfish ponds at a density of 62 carp/ha resulted in an almost total elimination of P. trivolvis. The farm is now successfully u sing a facility-wide stocking rate of 40 carp/ha, Laboratory experiments we re conducted to investigate the effect of salinity manipulation using NaCl on free-swimming trematode cercariae, the snail P. trivolvis, and catfish f ingerlings infected with the cercariae, A salinity of 2.5 ppt had a detrime ntal effect on snail survival, growth, and reproduction. Salinity did not h ave a negative effect on the other two aspects of the trematode life cycle tested (in fact, survival of both cercariae and infected catfish fingerling s showed a positive dependence on NaCl over the 0-2.5 ppt range). A field-e xperiment was then conducted in catfish ponds maintained at three salinitie s (2.5, 1.25, and 0.25 ppt) with rock salt, NaCl. Snail densities in ponds at 2.5 ppt salinity were consistently lower than in the other treatments an d no trematode infection was noted among snails or catfish in the 2.5 ppt s alinity ponds, Both the use of 2.5 ppt NaCl and black carp appear valuable management tools for controlling the digenetic trematode in catfish ponds.