Radiographic Benchmarks for Gastroliths in Juvenile Crocodiles—What’s Normal and What’s Not?

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

Charlotte R. Nix; Ellie R. John; Iain Cope; Katherine Hughes; Marie-Aude Genain

Background

Lithophagy, the deliberate ingestion of mineral material, is a known inherent behavior in crocodilians. However, limited literature exists to guide radiographic interpretation of gastroliths in crocodiles, particularly in distinguishing normal findings from clinically significant foreign bodies. This study aimed to characterize the number and relative size of radiopaque gastrointestinal gastroliths in a cohort of juvenile saltwater crocodiles in captivity and to assess potential associations between gastrolith burden and bodyweight over time.

Methods

A prospective observational study was conducted in 49 two-year-old juvenile saltwater crocodiles housed in a UK zoo. Dorsoventral coelomic radiographs were obtained without sedation at two time points separated by four months. Gastroliths were counted and classified relative to the length of the 11th dorsal vertebral body (D11) as sand, small (<0.5× D11), medium (0.5–1× D11), or large (>1× D11). Crocodile weight and morphometrics were recorded at both examinations. Statistical analyses evaluated changes in gastrolith number and size distribution over time, as well as associations with weight gain.

Results

Across both examinations, 1971 gastroliths were recorded, with a mean of 21 gastroliths per crocodile (range 0–98). Small gastroliths comprised 94% of all recorded stones. Only 4.5% of crocodiles had no gastroliths at either time point. Between examinations, there was a significant decrease in the number of small gastroliths per crocodile and a significant increase in medium-sized gastroliths. Total gastrolith counts decreased overall at the second examination. No significant correlation was identified between weight gain and gastrolith number at either time point. Crocodiles that died during the study period had significantly lower initial bodyweight and fewer small gastroliths compared to survivors. Postmortem findings did not implicate gastroliths as a cause of death.

Limitations

Radiographs were limited to dorsoventral projections due to practical and ethical constraints, preventing orthogonal evaluation. All subjects were juvenile crocodiles from a single collection, limiting generalizability to adult or wild populations. Gastrolith counting was performed by a single radiology resident, and inter-observer variability was not assessed. Potential superimposition of stones may have influenced counts of small gastroliths.

Conclusions

Large numbers of relatively small gastroliths are a normal radiographic finding in juvenile saltwater crocodiles and likely reflect healthy lithophagic behavior. As crocodiles increase in size, there appears to be a shift toward ingestion and retention of medium and larger gastroliths, potentially associated with buoyancy regulation. Radiographic presence of small gastroliths may indicate good appetite, whereas absence may warrant closer clinical monitoring. Careful environmental management remains essential to prevent ingestion of hazardous foreign materials.

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