In speaking about "basic" and "secondary" host, it is indispensable 

 to note that the "basic" host is not equivalent to the host which is histori- 

 cally initial (first, nobis ); this can be, as we shall try to show, observed 

 in a majority of the cases, but it is not essential because the meaning of 

 "basic" host is related to concrete conditions of the contemporary slice of 

 time and the initial host actually may not be the most favorable but the host 

 which was infected relatively recently. Inasmuch as we judge which is the 

 "basic" host according to the quantitative indices this is fully understandable. 

 As an example which confirms these considerations can be cited the data 

 on Nitzschia sturionis Abildgaard in the Aral Sea. If we judge by the number 

 (quantity, nobis) of infections, then it is understandable that Acipenser 

 nudiventris Lev. appears to be the basic host of the parasite. However, 

 we know that historically this species of fishes is the new host for N. 

 sturionis in the given body of water for they (the fish, nobis) were infected 

 by them {N_. sturionis , nobis) only in the 1930' s during the transfer of the 

 infected Stellated Sturgeon into the Aral Sea from the Caspian (Lutta, 1937; 

 Dogiel, 1947). The data about Gyrodactylus nemachili Bychowsky can serve 

 as another equally interesting example. This species was discovered in the 

 basin of the river Hi on eight species of fishes (and on one accidentally), 

 namely: Nemachilis strauchi (Kessl. ) in 20% of fishes, with an intensity of 

 from 1-15 individuals per fish N. labiatus (Kessl.) (14. 3%; 2-6 individuals 

 on the fish), ^ dorsalis (Kessl. ) (29. 0%; 1-20 individuals on the fish), 

 N. stoliczka i (Steind. ) (6.6%; 1-4 individuals on the fish), N. sewerzowi 

 G. Nik. (25.0%; 1-3 individuals on the fish). Phoxinus brachiurus Berg 

 (61. 8%; 1-15 individuals in the fish), Schizothorax pseudaksaiensis Herz. 

 (11. 1% equals one case and 1 specimen) and Sch. argentatus Kessl (3 39^ P- 247 



equals one case and one specimen) (Gvozdev, Agapova and Martehov, 1953). 

 Phoxinus brachiurus with its considerable infection appears to be the basic 

 host; however, there is no doubt that historically, representatives of the 

 genus Nemachilus are the most initial (primitive, nobis) hosts as is proven 

 by the morphological peculiarities of G. nemachili similar to those among 

 other species of Gyrodactylus from Cobitidae. However, the given example 

 demands careful analysis from the point of view of correlation of the existing 

 information about the relations of the hosts to each other in connection with 

 the above-mentioned rule. First of all we must note what is known about 

 the presence of hybrids between representatives of the genus Phoxinus and 

 Nemachilus (see Berg, 1912, page 10 ). Thus, the finding of D. nemachili 

 on both of these genera corresponds to the rule which was proposed by us 

 for Dactylogyrus . The finding of G. nemachili on both species of Schizothorax 

 is extremely rare and its intensity is minimal, which corresponds to the 

 above-mentioned rule about the frequency of occurrence on the moredistant 

 "secondary" hosts which both species of Schizothorax represent. 



The infection of five species of Nemachilus is of the greatest 

 interest. If we arrange them according to the percentage of infection and 

 intensity of invasion, we obtain the following list (from the stronger to the 

 weaker infection); N. dorsalis, ? N. sewerzowi, N. strauchi, N. labiatus. 



277 



