Comp. Biochem. Physiol. Vol. 78B, No. l, pp. 215-217, 1984 0305-0491/84 $3.00+0.00 Printed in Great Britain © 1984 Pergamon Press Ltd BIOLOGICAL ASPECTS OF AMAZONIAN FISHES I. RED BLOOD CELL PHOSPHATES OF SCHOOLING FISHES (GENUS SEMAPROCHILODUS: PROCHILODONTIDAE) A. L. VAL*; V. M. F. DE ALMEIDA-VAL*; A. R. SCHWANTESt and M. L. B. SCHWANTES~" *Departamento de Biologia Aqufitica e Limnologia, INPA, Instituto Nacional de Pesquisas da Amaz6nia, Caixa Postal 478, 69000 Manaus, AM--Brasil (Tel: 092-236-5700) and tDepartamento de Cirncias Biol6gicas, Universidade Federal de S,~o Carlos, Caixa Postal 676, 13560 S~o Carlos, SP--Brasil (Received 14 September 1983) Almtraet--1. Red blood cell soluble phosphates from Semaproehilodus taeniurus, S. insignis and a possible hybrid jaraqui-aqu, from Amazon basin, were studied by column chromatography. 2. The Semaprochilodus school and the jaraqui-aqu shows an intermediate percentage of total phosphorus content as GTP but not as ATP. 3. GTP/ATP ratio for jaraqui-aqu and S. taeniurus were 1.5 and for S. insignis, 3.0. INTRODUCTION Red blood cell phosphates have received increasing attention since some of them play important roles in oxygen transport due to their effect on the affinity of hemoglobin for oxygen. In fishes the most common erythrocyte phosphates are the adenosine triphos- phate (ATP) and guanosine triphosphate (GTP) (Bartlett, 1980). According to Bartlett (1980) the former varies from 3.1 to 21.2/~M of P (phosphate) per ml of red cells, while the content of the latter was found in a range of 0.5 to 16.8 #M of P/ml red cells. In some species the amount of GTP is higher than ATP. The genus Semaprochilodus include two species, S. insignis (large scale jaraqui) and S. taeniurus (small scale jaraqui) which migrate together in large schools (3-4 thousand individual of both species). Among them a rare (less than 1.0~) third type can be found--the jaraqui-aqu. Apparently, the jaraqui schools migrate twice a year; a spawning migration when they go into the 'encontro das hguas'--where the 'black' waters meet the 'white' ones, for reproduction and atrophic migration when, after the genetic migration, they go up Negro river for feeding. According to fishermen's belief, the jaraqui-agu is a hybrid between S. insignis and S. taeniurus. The present paper reports the qualitative and quantitative analysis of red cell phosphates of the three types of Semaprochilodus caught in the same school. MATERIALS AND METHODS The fishes were caught by seine netting in April, 1982, when they were migrating down the Negro river, 50 km from Manaus. Blood samples were taken from caudal vein with hep- arinised chilled syringes. Immediately after removing the plasma and washing the red cells with ice-cold isotonic saline solution, the samples of each species were pooled (except from jaraqui-a~:u where only one individual was caught) and the soluble phosphates were extracted with perchloric acid. Subsequent steps were carried out according to Bartlett (1959 and 1978). After releasing the phosphates obtainable by formic acid/ammonium formate, a linear gradient of hydrochloric acid (0 to IN) was passed through the column to look for inositol polyphosphate (Bartlett, 1982). RESULTS AND DISCUSSION The jaraquis show a hematocrit between 31-41~o and a hemoglobin concentration ranging from 10 to 14 g ~ (Amadio, 1983). Figure 1 shows the chromatographic profiles of the red blood cells phosphates of S. insignis, S. taeniurus and the possible hybrid--jaraqui-a~u. Table 1 shows the concentrations (in /tM/ml packed red blood cells) as well as the ratios GTP/ATP of the three types studied. The main phosphate components of the red blood cells of these fishes are the triphosphorylated nucleo- tides. As a percentage of total erythrocytes phos- phorous content the triphosphorylated nucleotides are 63~o in S. taeniurus, 79~o in S. insignis and 72~o in the aqu type. The latter shows an intermediate percentage between S. taeniurus and S. insignis. How- ever this intermediate concentration in jaraqui-aqu is due to the GTP concentration (38~o in S. taeniurus, 60~ in S. insignis and 45~ in jaraqui-a~u). On the other hand, the GTP/ATP ratio of the jaraqui-aqu resembles more S. taeniurus than S. insignis (Table 1). No evidence of inositol polyphosphate in red blood cells was found in a HC1 gradient elution. Our results agree with the findings of other authors, since GTP/ATP ratio is higher than 1.0 for the three types analysed. These authors found, study- ing several fish species, that in most cases GTP rather than ATP is the main intra-erythrocytic phosphate (Weber et al., 1975; 1976; Peterson and Poluhowich, 1976; Bartlett, 1978; Valet al., in preparation). Other studies have supported that GTP could be a 'choice' for the fish species by regulating their oxygen affinity when this phosphate is present in large amounts, since both anucleotides (ATP and GTP) are allosteric effectors of hemoglobin function (Bartlett, 1970; 1974; 1976; 1980; Weber and De Wilde, 1975; 215