Risk evaluation for fish health

Risk of the emergence of major aquaculture pathogens in the systems considered

Disease risk is one of the major constraints on the sustainability of aquaculture, and risk analysis is essentially about quantifying the risk, determining the consequences and possible scenarios, defining an acceptable level of infectious risk and the procedures to be put in place to manage this risk. These steps require a great deal of information and knowledge about the epidemiological factors of the diseases but also about other economic and social factors that may be involved in the health risk.

Infectious risk assessment is of increasing interest, especially when applied at the national level to i) manage the risk of introduction of exotic diseases; ii) implement health risk-based surveillance of fish farms. However, given the complexity and chronic lack of information on the health status of aquaculture systems, risk assessment in aquaculture has limited use.

A semi-quantitative model for ranking fish farms concerning the risk of introduction and spread of pathogens has been developed for salmonids (Oidtmann et al., 2011). The latter allows the definition of surveillance priorities according to the risk profile of these farms, thus allowing the possible implementation of a surveillance system specific to these facilities. Already used in tropical environments (Caruso & Lazard, unpublished data), in the AquaCAM project we propose a methodology and a biosecurity assessment grid for aquaculture adapted to the type of farming and especially to the conditions of local farms.

Based on the assessment of recognised risk factors grouped into “risk families”, these factors will be evaluated and weighted according to the seriousness of the risk they are recognised to pose. The methodology is based on assigning a rating to potential risks that may contribute to the contamination or emergence of a disease on the farm.  The higher the score, the higher the weight of the failures in the farm’s health safety

Broad web-based consultation is currently underway and a questionnaire has been submitted to international peers (experts in aquaculture and fish pathology) to collect their opinions and scores on these identified risks.

The analysis of these questionnaires will allow the drafting of an evaluation grid to assess the biosecurity of farms and more broadly the health “resilience” of production systems.  This approach will also be validated on a set of farms in the systems considered in the project, and classification of farms in terms of infectious risk could be proposed at the end of the project. This evaluation grid could be the first element for a national strategy of pathology surveillance in aquaculture based on the notion of risk or “Risk-Based Surveillance” (RBS).

This image has an empty alt attribute; its file name is RBS-MapPost-in-Fish-and-Food-safty-risk-Assement-1024x501.jpg

Longitudinal survey on the prevalence of Food-Borne Trematodes (FBT) in Silver barb and Red-tailed tinfoil

Some larval trematode known as flukes can be zoonotic affecting the liver or the intestine in humans. They represent a strong risk for consumers, especially in South East Asia. Cyprinid fish can be a carrier for these parasites and can transmit disease to a human. A study has been conducted to determine the prevalence of these parasites in Silver barb and Red-tailed tinfoil both fish are largely appreciated by Cambodian people. From June-2021 until now. we investigated fish from 6 provinces and Phnom Penh city of ​Cambodia to identify FBT species.

Nowadays, more than 800 Silver barb and Red-tailed tinfoil from aquaculture, Mekong River and markets in the Phnom Penh area were collected and analyzed. All fish samples were preserved on ice with a box and transferred to the laboratory of the Faculty of Fisheries, Royal University of Agriculture, for examination following the standard methods (WHO, 1995; modified by Chi et al. 2008).

Our study demonstrates that these fish have a relatively low prevalence of FBT than reported in other studies. However, our study has shown that many factors can influence the parasite pressure in fish (Seasonal patterns, species, geographic location, size of fish, facilities …). Our study continues to investigate on this subject.