Gyrodactylus thymalli ?it?an, 1960 and G. salaris Malmberg, 1957 have an indistinguishable ribosomal internal transcribed spacer (ITS) DNA sequence, but exhibit surprisingly high levels of intra- and interspecific sequence variation of the mitochondrial cytochrome oxidase I (CO1) gene. To test whether different populations of these reportedly very similar species could be discriminated using morphometric methods, we examined the morphometry of four different populations representing different mitochondrial clades. Twenty five point-to-point measurements, including five new characters of the attachment hooks, were recorded from three Norwegian laboratory populations (G. salaris from the Rivers Lierelva and Rauma, and G. thymalli from the River Rena), and from one wild population of G. thymalli from the River Test, UK. The Norwegian populations were kept under identical environmental conditions to control for the influence of temperature on the haptoral attachment hooks. Data were subsequently subjected to univariate and linear stepwise discriminant analyses. The model generated by the linear stepwise discriminant analysis used 18 of the 25 original variables, the first two roots accounting for 96.6% of the total variation between specimens. The hamulus shaft length accounts for 66.7% of the overall correct classification efficiency. Based on morphometry, all specimens were assigned to the correct species. Apart from three specimens of G. salaris from the River Lierelva population which were misclassified as belonging to the G. salaris Rauma population, all specimens were assigned to the correct population. Thus, populations of Gyrodactylus identified by mtDNA can also be discriminated using morphometric landmark distances.

The challenges and problems of managing good biosecurity are wide‐ranging and multifactorial with many compounding factors to pre‐dispose farmed stocks to an increased risk of infection with consequential stock losses. Many challenges are anthropogenic in origin and may be the result of the physical location (site) and/or the poor design of the production facility (i.e., water re‐use; lack of zoning based on biosecurity risk, etc.) as well as from inappropriate decisions and practices made once the site is in production (i.e., pushing the system for increased biomass production). There is a need for better regulation and health legislation across aquaculture—an industry that embraces the culture of >500 species. In the absence of regulatory frameworks and culture guidelines, it is difficult for farmers to apply certain measures such as maximum stocking densities and maximum allowed biomass, conduct disease surveillance and regular health checks, and report diseases to relevant authorities for advice. In this review, we have identified several issues which are continuing to challenge the design and implementation of efficient and effective biosecurity strategies and protocols at all levels, requiring attention over the coming decade. They are, not in any order of priority: (a) healthy seed, (b) emergency preparedness and response, (c) diagnostics, (d) microbial management at the production level, (e) disease and pathogen surveillance, (f) trade in aquatic species, (g) policies and regulatory framework, (h) welfare, (i) research and technology development, (j) antimicrobial resistance, (k) non‐conventional ways of pathogen transfer, and (l) Progressive Management Pathway.

Over the past 80 years, tilapia have been translocated globally for aquaculture; active production is recorded in >124 countries. Of 7 million tonnes of tilapia produced in aquaculture, 79% is from 79 countries outside the natural range of tilapia. Capture fisheries account for a further 723,627 tonnes of tilapia, and >47% of this is landed from established invasive populations outside Africa. Tilapias host a rich fauna of parasites, many of which have been translocated with their hosts. This review summarises >2500 host–parasite records from 73+ countries and >820 recorded tilapia translocations (provided in the supplementary materials). This work focuses on the notable pathogens that threaten the health of cultured populations of tilapia, providing a description of their pathology and includes species that also have substantial impacts on wild tilapia populations, where relevant. For each major parasite taxonomic group, we highlight which parasites have been translocated or have been acquired from the new environments into which tilapia have been introduced, together with remarks on standard treatment approaches and research on them and their management and control. Regarding the theme ‘Tilapia health:quo vadis?’, Africa has enormous potential for aquaculture growth, but substantial knowledge gaps about tilapia parasites in many African states remain, which creates associated production and biosecurity risks. For each parasitic group, therefore, the risks of parasite translocation to new regions as tilapia aquaculture industries expand are highlighted.