DISEASE OF SALMON 



37 



lowish and generally tinged with blood. There 

 was some muscular necrosis in the anal region. 



Scoliosis developed during May in about 0.1 

 percent of the original population in the six 

 troughs of diseased fish, and some fish with re- 

 tracted heads were observed (see fig. 3). 



The rest of the blueback fingerlings exhibited no 

 characteristic disease symptoms throughout the 

 summer, but during the first week of September, 

 when water temperatures became progressively 

 colder, diseased lish were again seen. At this time 

 the fish were about 4 inches long and 8 months old. 

 Diseased fish showed a reddened large intestine 

 and a watery, bloody, yellowish discharge from 

 the anus. About half of these had areas of fungus 

 growth, predominately at the base of the pectoral, 

 pelvic, or anal fins. These were the sites where 

 hemorrhagic areas were seen on diseased lish in the 

 spring. FungUS generally indicates debilitation 

 or the presence of necrotic tissue. In September 

 approximately half of the diseased fish exhibited 

 spinal deformities: of these 60 percent had re- 

 tracted heads. 30 percent scoliosis, and 1(1 percent 

 lordosis (see fig. 1). Many lish showed no ex- 

 ternal signs of the disease other than these abnor- 

 mal body shapes. A number of lish with spinal 

 deformities had a surface growth of fungus, but 

 autopsv of a few fish with scoliosis revealed no 

 internal abnormalities. 



Therapeutic Tests 



The routine hatchery treatments of 1-hour 

 baths in solutions of 1:4,000 formalin or of 

 1:100,000 pyridylmercuric acetate failed to in- 

 fluence the mortality rate. Therefore, sulfona- 

 mides and antibiotics were used experimentally 

 on the fish that showed evidence of the infection. 

 (See figure 2.) 



When the fish in a trough became diseased they 

 were divided into several groups and transferred 

 to other troughs. The therapeutic agents were 

 added to the food. Sulfamera/.ine, sulfaguaui- 

 dine, sulfadiazine, and sulfamethazine were each 

 used at the rate of 10 grams to 100 pounds of fish 

 a day. The antibiotics were also added to the 

 food at levels for 100 pounds of fish as follows: 

 Aureomycin 1.5 grams in experiment A and 5 

 grams in experiment D; terramycin 2.5 grams; 

 Chloromycetin '2.5 grams; streptomycin 10 grams; 



and penicillin 1 million units in experiment C and 

 10 million units in experiment I). 



The cumulative mortalities, shown in figure 2. 

 are expressed as the percentage of the total mor- 

 tality for each group. There was some difference 

 in the total numbers of fish in the different troughs. 

 At the beginning of an experiment, the number 

 of fish in each trough was necessarily an estimate, 



Figure 1. — Living blueback-salmon fingerlings from the 

 Leavenworth station, showing lordosis in a 4-inch fish 



(upper) anil scoliosis in a 3-inch lish I lower). 



and actual counts were made as the lish died. In 

 experiment C, only an estimate is available ( 5,000 

 lish per trough) since the experiment was termi- 

 nated at an early date because t he drugs apparently 

 were ineffective, and it was desired to set up 

 another experiment at a higher drug level. 



None of the therapeutic agents tested seemed to 

 be of any benefit: the mortalities continued. 

 Practically all fish died in each experiment re- 

 gardless of the therapeutic agent employed. 



