Chapter 9: Blood and Circulation
Arthur H. Houston
In this chapter, consideration will be given to the variables most commonly used to characterize hematological status and circulatory flow, and to methods for their assessment. An enormous literature pertinent to these topics now exists. Mahajan and Dheer (1979) noted that some 900 articles had been published on the subject of fish hematology alone prior to 1970. At least 100 new papers concerned with blood and circulation have appeared each year since. Consequently, the choice of methods to be considered here has been limited primarily to those of general utility.
Most fishes have similar circulatory systems. Their systems are largely or wholly closed, and the heart, branchial and systemic microcirculatory beds, and macrocirculatory vessels are linked in linear array. The systems differ in detail, however, and prior examination of vascular anatomy is essential when bloodsampling procedures are developed, particularly for an unfamiliar species. Although radioautographic examinations are useful (Bell and Smart 1964), such preliminary studies of vascular anatomy are facilitated by simple casting methods. Both flexible or rigid vascular casts can be prepared readily, but the latter are more generally useful because they can be used for both dissection and permanent reference mounts. Smith and Bell (1976) and Bell (1978) adapted casting techniques outlined by Tompsett (1970) for application to fishes. Bell (1978) recommended use of the Batson Anatomical Corrosion Kit, available through Polysciences Inc. of Warrington, Pennsylvania. The only additional equipment needed is a specimen tray (40 x 15 x 0.5 cm, made of clear plastic with 45-cm-long stainless steel wires corner-mounted and linked to form a handle) and a standard caulking gun modified to hold a 20-mL disposable plastic syringe. The latter provides better control over injection than can usually be achieved with a hand-held syringe.