# Rapid parasitological indicators as practical biosecurity tools in inland Nile tilapia (Oreochromis niloticus) aquaculture: A national multiregional two-season survey in Saudi Arabia

## TL;DR

This study shows that checking for common parasites in Nile tilapia can help detect biosecurity issues in Saudi aquaculture, offering a low-cost way to improve farm health.

## Contribution

The study introduces rapid parasitological screening as a practical biosecurity tool for inland Nile tilapia aquaculture in Saudi Arabia.

## Key findings

- Trichodina and Cichlidogyrus were the most prevalent parasites, found on nearly all farms.
- Seasonal and water quality factors significantly influenced parasite presence and diversity.
- Simple screening methods can detect biosecurity risks and support early disease prevention.

## Abstract

The inland aquaculture sector in Saudi Arabia has expanded rapidly, with Nile tilapia (Oreochromis niloticus) becoming the dominant cultured species. However, limited national surveillance has restricted early detection of parasitic infestations that could indicate breaches in farm-level biosecurity. This study aimed to evaluate low-cost parasitological screening as a practical indicator of biosecurity performance by assessing parasite prevalence, diversity, and predictors across inland farms during two seasons.

A sample of 30 fish from each farm was examined from 25 inland aquaculture sites sampled in summer and winter (2022–2023). External and internal parasitic infestations were evaluated through wet smears of the skin, fins, and gills, and by compression techniques for digeneans. Water quality parameters, serum cortisol levels, and farm management data were recorded. Parasites were identified to the genus-level. Predictors of infestation were analyzed using binary logistic regression followed by generalized linear mixed models.

Six parasite groups were detected, with infestations recorded on all farms. Trichodina spp. showed the highest farm-level prevalence (96%) and fish-level prevalence (54.3%), followed by Cichlidogyrus spp. (92% of farms; 56.9% of fish). Dactylogyrus, Ambiphyra, Gyrodactylus, and Centrocestus were variably present, with the eastern region displaying the lowest diversity. Most infestations were mild. Significant predictors varied by parasite type: summer season increased the likelihood of Centrocestus, Dactylogyrus, Cichlidogyrus, and Ambiphyra; low pH strongly predicted monogenean and sessile ciliate infestations; dissolved oxygen and fish length also contributed to parasite-specific patterns. No clear association existed between infestation and elevated cortisol levels.

This nationwide two-season assessment shows that simple parasitological screening, especially for Trichodina and Cichlidogyrus, offers quick, affordable signs of biosecurity breaches in inland O. niloticus aquaculture. The presence of parasites indicates past or current risks of pathogen introduction, highlighting the importance of better quarantine procedures, water quality management, and following national biosecurity guidelines. Regular quarterly parasitological checks, combined with water quality testing and improved farm hygiene, can enhance early detection and reduce the spread of disease across Saudi Arabia’s aquaculture industry.