Radiographic evaluation of gastroliths in a group of 49 juvenile saltwater crocodiles ( Crocodylus porosus ) in the UK

BACKGROUND: Gastrolith ingestion is a known inherent behaviour in crocodiles. However, the interpretation of coelomic radiographs in crocodilians is challenging due to the limited informative literature in this field. METHODS: Dorsoventral coelomic radiographs of 49 juvenile saltwater crocodiles (Crocodylus porosus) were acquired twice, with an interval of 4 months. Any gastroliths present were evaluated and classified as sand, small, medium and large, relative to the size of the crocodile, by comparing the gastrolith size to the length of the 11th dorsal vertebral body. RESULTS: A total of 1971 gastroliths were recorded during the two examinations (mean of 21 per crocodile, range 0‒98). Small gastroliths were the most commonly recorded (94%). There was no significant correlation between weight gain and gastrolith numbers in either examination (p = 0.506 and 0.2034). There was a significant reduction in small gastroliths (p = 0.034) and a significant increase in medium gastroliths (p = 0.023) between examinations. LIMITATIONS: All radiographs were performed on a cohort of juvenile crocodiles at the same collection. Orthogonal lateral radiographic projections were not performed due to practical and ethical limitations. CONCLUSIONS: Large numbers of relatively small gastroliths are likely a normal radiographic finding in juvenile crocodiles. As crocodiles increase in size, ingestion and retention of medium/large gastroliths may reduce body buoyancy to aid in increasing dive times and hunting of larger prey.