Longevity of Fishes in Captivity 213 



It is generally known that fishes represent a physiologically 

 highly diversified group of vertebrates, and attempts to 

 maintain them in so-called standard aquarium conditions 

 regardless of environmental origin are fraught with danger and 

 will invariably be reflected in a short lifespan in captivity. As 

 environmental origin is recognized as important in aquarium 

 management, it is the practice in the New York Aquarium, 

 in so far as it is possible, to diversify physical and chemical 

 conditions such as temperature, pH, surface-volume ratios, 

 conditioning factors, w^ater movements, salinity and illumina- 

 tion. As a result of such management we have been able to 

 increase our survival rates significantly. Thus, in 1940, our 

 last full year of operation at the New York Aquarium at the 

 Battery, average longevities were as follows: marine fishes 

 9*58 months, temperate freshwater species 24*50 months, 

 and tropical freshwater fishes 11-22 months. The mortality 

 rate for the year was 169 per 1,000. 



Infectious diseases are the primary causes of death in 

 aquaria (Nigrelli, 1940, 1943). It is generally known that 

 fishes are susceptible to a large variety of metazoan parasites, 

 but what is not common knowledge is that they are also 

 prone to infections by pathogenic micro-organisms that are 

 similar in many respects to those responsible for diseases in 

 man and other mammals. For example, to mention a few, 

 fishes are susceptible to infections by viruses, Rickettsia, 

 PseudomonaSf Proteus, diphtheroids, tubercle bacilli (Myco- 

 bacterium), Monilia and other mycotic organisms. They are 

 also susceptible to such protozoans as trypanosomes, haemo- 

 gregarines, coccidians, babesioids, and Toxoplasma, in addition 

 to such ubiquitous parasites as flukes, tapeworms, nematodes 

 and acanthocephalans. The most important aetiological 

 agents of fish diseases, however, belong to a subclass of 

 Sporozoa called cnidosporidians. These are truly spore- 

 producing parasites in which transmission is direct, i.e. by 

 ingestion of the spore. During the course of routine autopsies 

 at the New York Aquarium in the last 25 years, the present 



