The Host Range of Saprolegnia Parasitica

Summary

The host range of Saprolegnia parasitica Coker was investigated by means of controlled inoculations on accurately identified fish and amphibians of as many species as could be obtained.

1.	It was found that there was a marked difference in the resistance of various species of hosts to the pathogen. Ameiurus nebulosus, Erimyzon sucetta, Esox reticulatus, Salmo sebago, S. irideus, S. fario and Trituras viridescens were found to have a very low resistance to the disease. Semotilus atromaculatus, Pomoxis sparoides, Eupomotis gibbosus, Morone americana, Perca flavescens and Fundulus heteroclitus showed a somewhat greater resistance, while Crassius auratus, Lebistes reticulatus, Micropterus salmoides and Rana pipiens had a high resistance to the disease. Only Anguilla chrysypa was found to be immune.
2.	Injury greatly lowered the resistance of the majority of the species of hosts to the disease.
3.	The symptoms of the disease were identical for the various species of fish used in these experiments.
4.	Fish were frequently observed to eat living mycelial mats of Saprolegnia parasitica but apparently suffered no harm thereby and did not develop intestinal mycosis.
5.	Except for one aberrant case, there was no evidence that the death of the host was caused by smothering.
6.	From observations made during the course of this investigation the writer suggests three possible causes of death to the host: (a) the destruction of tissue, (b) the formation of toxic materials, and (c) the dilution or dehydration of body fluids resulting from the destruction of areas of protective epidermis.
7.	The following species of fish and amphibians were added to the previous records of hosts of Saprolegnia parasitica Coker: Ameiurus nebulosus Le Sueur, Erimyzon sucetta Lacépède, Crassius auratus L., Semotilus atromaculatus Mitchill, Salmo sebago Girard, S. irideus Gibbons, S. fario L., Fundulus heteroclitus L., Lebistes reticulatus Peters, Esox reticulatus Le Sueur, Pomoxis sparoides Lacépède, Eupomotis gibbosus L., Micropterus salmoides Lacépède, Perca flavescens Mitchill, Morone americana Gmelin, Triturus viridescens Rafinesque and Rana pipiens Schreber.