LAUSR

Urinary calculi are observed in some cultured marine fish larvae and may negatively impact larval health and survival. This study assessed urinary calculi in striped trumpeter Latris lineata larvae from hatching to 28 days post-hatching (dph). The prevalence of urinary calculi was variable over time and ranged from 15% to 50%, whereas the average size of calculi increased with larval age. Urinary calculi were semi-translucent, light cream to white colour with irregular morphology and a uniform internal structure. The calculi resulted in pressure atrophy causing a distended epithelium of the urinary bladder of fish with calculi. The calculi were predominantly formed of calcium hydrogen phosphate (CaHPO4 ). Routine assessment of the prevalence of urinary calculi in marine fish larvae is recommended, along with other parameters, to monitor larval quality and inform hatchery management actions.