MICROHEMATOCRIT AS A TOOL IN FISHERY 

 RESEARCH AND MANAGEMENT 



INTRODUCTION 



Hematology is the study of blood or the 

 sum of knowledge about blood. Much of this in- 

 formation consists of measurements of value of 

 the components of blood under normal and ab- 

 normal conditions. Most readers have had red 

 and white cell counts or hemoglobin determina- 

 tions made during routine medical examinations. 

 Less familiar, perhaps, but even more important 

 is the hematocrit determination. 



The value and significance of hematologic - 

 al examination, and that of hematocrit in particular, 

 may best be conveyed to readers not familiar with 

 these procedures, by quotations from authoritative 

 sources: 



"Since a change or lack of change in the blood 

 picture' is a fundamental characteristic of practic- 

 ally every physiologic or pathologic state, hemato- 

 logic findings are among the most valuable and 

 most generally useful of all laboratory diagnostic 



aids The field of clinical hematology is 



well within the reach of every practitioner. The 

 laboratory methods are not really demanding, and 

 diagnostic interpretations are generally not diffi- 

 cult" (Wells, 1956). 



"Determination of the hematocrit reading, the 

 erythrocyte count and the hemoglobin concentra - 

 tion are all used in evaluating the erythrocyte 

 content of blood. The hematocrit determination 

 is the most accurate of these methods inasmuch 

 as it is not subject to the rather large errors in- 

 herent in pipetting and diluting blood according to 

 the other methods" (Strumia fit §1., 1954). 



"The hematocrit reading, or the percent- 

 age of packed cells in the peripheral blood is one 

 of the most important of all clinical constants . 

 Because of its simplicity and hi^ degrees of re- 

 producibility, this procedure is most useful as a 

 routine for detection of anemia, (Wells, 1956). 



Some aspects of fish hematology have been 

 reported. Hematocrit determinations have been 

 given in some of the more recent works which are 

 here briefly reviewed. The most complete com- 



parative study on the blood of vertebrates was 

 made by Wlntrobe (1934) who Introduced hemato- 

 crit to hematology. He found that hematocrit, 

 hemoglobin, and mean corpuscular hemoglobin 

 concentration were uniform among all vertebrates, 

 but that the number of red cells was the most 

 variable . The hematocrit values in fish range 

 from about 5 to about 60. This unusually great 

 amplitude probably results from the fact that 

 many of the examined fish were kept under ab- 

 normal conditions. The author makes it clear, 

 therefore, that his figures should not be con- 

 sidered as representative for the different species 

 of fish he examined. Wlntrobe' s data show that 

 among warm blooded vertebrates the hematocrit 

 values were mostly between 35 and 50 . 



Studies on marine fishes reported by Klsh 

 (1949) show similar hematocrit values to those 

 found by Wlntrobe, but with a narrower amplitude 

 (20-51). Hematocrit values for freshly caugjit 

 carp (Cyprinus carpio ) and northern pike ( Esox 

 luclus) are of the same magnitude (Vars 1934) . 

 Similar hematocrit values for carp and eastern 

 brook trout (Salvelinus fontinalis) were reported 

 by Field etal_. (1943) and for sea- lamprey 

 (Petromyzon marlnus) by Thorson (1959). Repeated 

 hematocrit determinations for individual fish dur- 

 ing a period of several months show that these 

 values vary considerably. Whenever a fish sup- 

 posedly became diseased or lost appetite due to 

 undetermined causes, the hematocrit values be- 

 came much lower (Young, 1949). So far as I 

 could establish, Benditt, Morrison and Irwing 

 (1941) were the first to use capillaries for 

 hematocrit determination in fishes . They found 

 for Atlantic salmon ( Salmo salar salar) in brack- 

 ish water the mean hematocrit value was 39 and 

 in fresh water the value was reduced to 25. Watson 

 et al. (1956) recorded 47 as the normal mean micro- 

 hematocrit value in fingerling sockeye salmon 

 ( Oncorhyncus nerka) . In the same lot of salmon 

 apparently infected with a specific pathogenic virus 

 the hematocrit values were significantly lower . 

 Hematocrit values are not included in the recent 

 manual "The Physiology of Fishes" (Brown, 1957). 



Hematological examinations of fish are 

 usually made either in the course of research or 



