USE OF DIAGNOSTIC X-RAY FOR 

 DETERHINING VERTEBRAL NUTffiERS OF FISH 



Use of vertebral numbers to delineate 

 races, or popiilations, has had wide appli- 

 cation in fishery research (Clark, 19k7; 

 McHugh, 1951; Tester, I9U8, et al.)- Often- 

 times, however, this character is ignored 

 in such studies because of the great amount 

 of tipie and effort required in dissection 

 of vertebral columns in order to determine 

 accurately tlie number of vertebrae. Fur- 

 thermore, investigators frequently are 

 reluctant to commit a valviable collection 

 to dissection as the specimens subsequently 

 are of little value for further study. 

 Radiographs, therefore, not only furnish a 

 means of rapidly determining vertebral 

 counts of individual fish, but provide a 

 permanent record of the vertebral column 

 for future reference. 



The adaptability of X-rsys to the 

 study of fish was first emphasized in this 

 country by Gosline (19U8) who produced 

 satisfactory radiographs of several fresh- 

 water species ( Ameiuru s melas me las , 

 Ictalurus furcatus^ Ictalurus lacustris 

 p uncatus , Notemigonus crysoleucas , and 

 Percinaeaprodes ) with a used radiographic 

 unit obtained from the War Assets Adminis- 

 tration. Since 19h5 several research 

 papers note the use of X-rays in deterinin- 

 ing the vertebral numbers of fish (McHugh, 

 19?1,- Bonhsm and Bayliff, 1953; Howard 

 1951; Bailey and Gosline, 1955), but little 

 detailed information concerning X-ray 

 technique is given. 



It is the ptu'pose of this paper to (l) 

 describe the types of X-ray machines com- 

 monly used in fish radiography, (2) describe 

 necessarj'' accessorj'' equipment and supplies, 

 (3) present techniques for successful reso- 

 lution of fish vertebrae by radiography, 

 (h) show a cost analysis of investment and 

 operation of an X-ray machine, and (5) 

 furnish a parts list and a circuit diagram 

 from which an efficient, inexpensive machine 

 may be assembled. The material presented 

 is the result of nearly two year's work with 

 X-ray methods in routine determinations of 

 vertebral counts of many thousands of Atlan- 

 tic menlisden (Brevoortia tyrannus ) . 



TYPES OF X-RAY MACHINES 



Two main types of X-ray machines have 

 been commonly used in fish radiographyj 

 these may be classified as either soft or 

 hard ray emitters, depending on the applied 

 kilovoltage (kv.). Soft-ray machines oper- 

 ate from, approximately 10 kv. (Grenz-rays) 

 to 25 kv. (diffraction units) and are most 

 suitable for examining small specim.eas. 

 X-ray tubes operating on low kilovoltages 

 have small focal spots, or anodes, from 

 which radiation is emitted as a' narrov; bea^n 

 for short distances. Thus, greater accu- 

 racy and photographic sharpness is to be 

 expected as there is less likelihood of 

 interference from scattered or reflected 

 radiation. This type of radiography, how- 

 ever, has not proven advantageous over the 

 higher kilovoltage radiographic types for 

 routine examination of fish vertebrae. 

 Bonham and Bayliff (ibid.), for example, 

 reported having successfully radiographed 

 specimens of G ambus ia measuring 9 mm. stand- 

 ard length with a soft-ray machine, but 

 were unable to resolve the vertebrae of 

 small salmon ( Oncorh^^Tichus ) and eel pouts 

 ( Lye odes brevipes ) less "than 35 mm. stand- 

 ard length. The probable reason for this 

 apparent inconsistency of results is that 

 vertebrae of slow-growing fish become m.ore 

 dense at a relatively smaller body length 

 than those of relatively larger, fast-grow- 

 ing species. It follows then that the 

 density of the vertebrae imposes limitations 

 on soft-ray as well as hard-ray machines 

 for successful resolution. 



Hard-ray emitters, or diagnostic ma- 

 chines, operate on applied kilovoltages of 

 approximately 25 to 100 kv. The focal spots 

 on such machines are necessarily larger than 

 on lower kilovoltage tubes as the energy 

 imput is potentially much greater (Clark, 

 19ltO). Unless the energy is spread over a 

 greater surface, melting and destruction of 

 the anode would result. Kore interference 

 from scattered or reflected radiation could 

 be expected due to the increased size of 

 the diametric field of effective radiation 

 produced by the larger focal spot. However, 



