TUCKER AND LAROCHE: RADIOGRAPHY 



39 



Fig. 15. Positive image of radiograph of a southern flounder (Paralichthys tethosligma) larva, 9.7 mm SL, stored m 7% borax buffered seawater 

 formalin for seven years. Radiographic exposure data: Faxitron Model 43805N; Kodak Type R film; source to film distance. 46 cm; 9 kv; 600 

 mAs; under helium. Intemegative processing data: radiograph was projected onto 4 in x 5 in professional copy film (Kodak 4125) with an Omega 

 (4 in X 5 in) Pro Lab Enlarger; exposure was 1 s at f S'/j; film was developed in Kodak HCl 10 (dilution E) for 5 min at 23 C. Print processing 

 data: a positive pnnt was made on Kodak Polycontrast Rapid 11 RCF paper using a polycontrast no. 3 filter in the Omega enlarger; exposure was 

 5 s at f 5.6; print was developed in Kodak Ektaflo diluted to simulate Dektol 1:1, at 23 C. (The intemegative and printing procedure was devised 

 and performed by Tom Smoyer of Harbor Branch Foundation.) 



and high contrast. The single emulsion is necessary for avoiding 

 two images (on both sides of the film). Coarser grained and 

 lower contrast films will produce inferior radiographs. 



Exposures should not be longer than about 5 min, and for 

 many specimens 5 min is too long. Larvae will quickly desiccate, 

 and even if not damaged, may shrink and cause blurred images. 

 Specimen damage or image blurring will determine the mini- 

 mum size of larvae that can be x-rayed. Specimens can be pro- 

 tected by an overlying sheet of dry-cleaning plastic if care is 

 taken to remove bubbles. During exposure, unneeded portions 

 of the film can be protected for later use with lead vinyl masks. 



The manufacturers' instructions for mixing chemicals and 

 processing films should be followed as closely as possible. Fre- 

 quent agitation of the film while it is developing, rinsing, and 

 fixing is important to ensure uniformity of chemical reactions. 

 Both undeveloped and developed films should be stored away 

 from light, heat, humidity, and chemical fumes (particularly 

 formalin, alcohol, and hydrogen peroxide). Radiographs are best 

 observed directly, emulsion side up, with a dissecting or phase 

 contrast microscope. Printing of radiographs is best done via 

 an intemegative (Fig. 15). This compresses the tonal range so 

 that finer detail can be preserved in the print. 



The major limitation of the technique is probably inadequate 

 radiation intensity at low kv. This limit may have been reached 

 with x-ray units equipped with 10 mil beryllium windows. Sat- 

 isfactory radiographs of 4-1 5 mm larvae have been made at 8- 

 10 kv and 300-800 mAs (milliamperes x seconds). Some im- 

 provement can be expected if the air is replaced with helium; 

 however, exposure time will eventually become prohibitively 

 long. 



Because machine and specimen characteristics vary, a stan- 

 dard formula for producing high-quality radiographs cannot be 

 provided. At least initially, the larval fish radiographer must 

 proceed by trial and error with the machine and specimens at 

 hand. As familiarity develops, the results will improve signifi- 

 cantly. We stress that an accurate and detailed logbook con- 

 taining specimen and exposure data should be kept, and that 

 procedures should be standardized. 



(J.W.T.) Harbor Branch In.stitiition, Inc., RR l,Box 196-A, 

 Fort Pierce, Florida 33450; (J.L.L.) Gulf Coast Re- 

 search Laboratory, East Beach Drive, Ocean Springs, 

 Mississippi 39564. 



