Report No. 2 (1917). 



A WIW PROTOZOAN CAUSE OF WIDESPREAD MORTAirFY 

 AMONG MARINE FISHES* 



BY 

 JAMES HORNELL, F.L.S., 



Government Marine Biologist, Madras, 



Widespread fish mortality is a well known phenomenon on the 

 Malabar and South Kanara coasts ; its recurrence yearly along 

 certain stretches of the coast line is regular, though its intensity 

 varies within wide limits. In certain seasons it is local in occur- 

 rence and affects only a few species close inshore ; at others, by 

 no means of annual or regular occurrence, many and diverse kinds 

 are involved, and it may affect large shoals both close in and at 

 several miles distance from the land. 



Until the present, I believe no detailed investigation of this 

 phenomenon has been attempted; neither has any satisfactory 

 explanation been given, although various hypotheses have been 

 advanced. My attention has been given to the subject intermit- 

 tently for several years past, but till last year I was never able to 

 spare the time necessary for a continuous investigation at a period 

 coincident with the occurrence of the phenomenon. 



Before detailing my own observations and the conclusions 

 arrived at, I may note that all Malabar fishermen whom I have 

 questioned agree in saying that every year after the passing of the 

 rainy season and the subsidence of the south-west monsoon, if 

 there be a continuance of fine weather for a week or ten days, 

 with plenty of sunshine, and a weak coastal current, the water 

 inshore becomes turbid and discoloured, brownish or reddish in 

 tint ; that this water has such poisonous effects upon fish that large 

 numbers become affected and eventually die. The first effect of 

 the poison is to make the fish sluggish and at this stage, as I have 

 myself seen, boys and men crowd to the shore and make great 

 hauls of the dying fish. Fishermen further state that if favourable 

 conditions continue, the colour of this foul water changes and 

 becomes distinctly redder, and emits a stench so strong as to be 



* A paper read before the Zoological section of the Jndian Science Congress held 

 at Bangalore, January 191 7. 



