24 
Transactions of the Royal Society of South Africa. 
connection. These are, briefly, that, at a point on the South Coast, marking 
the meeting place of the South-Polar and Equatorial waters, there is a 
mortality amongst fish, and possibly other marine animals, which may be 
slight or well marked but occurs annually and at definite periods of the 
year. A similar occurrence is found on the West Coast, at a point in the 
branch of the South-Polar current which passes up the West Coast of 
South Africa. The object of the present paper is to record some facts 
bearing upon this subject from a different point of view. 
The H.M.S. " Challenger," namesake of the " Challenger " of zoological 
fame, arrived in Simons Bay in January, 1919, from British East Africa, 
Zanzibar and other Eastern ports. She had on board a number of live fish, 
which had been collected at various places, and kept alive in a tank of circu- 
lating water. Dr. N. Spencer Nairne, Surgeon, who, along with the 
officers of the ship, were instrumental in securing and keeping the fish alive, 
readily assented to transfer the fish to the tanks of the Government Marine 
Laboratory at St. James, near Cape Town, thus affording a unique oppor- 
tunity of testing the effects of the colder waters of the Cape seas on 
tropical fish. 
The following is a list of the fish, with their localities ; 
Carnax djeddaba . Four from Dar es Salaam Harbour. 
Carnax affinis . One from Dares Salaam Harbour. 
Lutianus johnii . One from Port Amelia, Portuguese E. Africa. 
Holocentrum rubrum . One from Port Amelia, Portuguese E. Africa. 
Batistes aculeatus . One from Mnazi Bay, Portuguese E. Africa. 
Epinephelus sp. . Two from Zanzibar. 
The fish were safely transferred in barrels by steam launch and placed 
together in a large tank (14 x 5 ft.). Batistes had, however, to be removed to 
a separate tank on account of its aggressive habits. The others adapted them- 
selves almost at once to their new surroundings, the two species of Carnax 
swimming about together, the Epinephelus (rock-cod) remaining, as is the 
habit of these fish, under the shelter of the rock- work in the tank. 
A marked feature of all the fish was the apparent ease with which they 
adapted themselves to their new surroundings, and more especially their 
greater activity as compared with that of the Cape fishes in captivity. The 
latter feature was more conspicuous in the case of the Carnax. Their 
movements were very rapid and sustained, and it was soon found that no 
Cape fish of a small size were immune from their attacks. This was 
specially so in the case of the common Cape mullet (Mugil cajnto), which 
happened to be in the tank with them. 
All of the fish throve well ; they became plumper, and some abrasions, 
caused doubtless by their confinement in the smaller tank on board the 
"Challenger," healed up rapidly, and one might wonder why those warm- 
water fish had not naturally spread to the apparently more congenial con- 
