Behavioural adaptations of argulid parasites (Crustacea: Branchiura) to major challenges in their life cycle

Fish lice (Argulus spp.) are obligate ectoparasites, which contrary to most aquatic parasites, retain the ability to swim freely throughout the whole of their life. In fish farms, they can quickly increase in numbers and without effective control cause argulosis, which results in the reduced growth and survival of their fish hosts. The morphology of Argulus spp, including their sensory organs, is suitable for both parasitism and free-swimming. By spending a considerable amount of time away from their host, these parasites risk being excessively dispersed, which could endanger mating success. Here we present a review of recent studies on the behaviour of Argulus spp, especially the aggregative behaviour that mitigates the dilution of the parasite population. Aggregation of parasites, which is especially important during the period of reproduction, occurs on different scales and involves both the aggregation of the host and the aggregation of the parasites on the host. The main behavioural adaptations of Argulus spp, including searches for hosts and mates, host manipulation and host choice, are all focused on the fish. As these ectoparasites repeatedly change hosts and inflict skin damage, they can act as vectors for fish pathogens. The development of environmentally friendly measures for the control and prevention of argulosis needs to take into account the behaviour of the parasites.peerReviewe

Potential of DIVA vaccines for Fish

The expanding aquaculture industry continues to encounter major challenges from highly contagious viruses. Control and eradication measures for lethal and economically damaging notifiable viral diseases involve ‘stamping out’ policies and surveillance strategies. Mass-culling of stock and restricted movement of fish and fish products, used to control the spread of notifiable diseases, has considerable impacts on the trade of fish products. Although effective, these measures are expensive and ethically complex and could possibly be reduced by emulating innovative vaccination strategies used by the terrestrial livestock industry. DIVA (differentiating infected from vaccinated animal) strategies provide a basis to vaccinate and contain disease outbreaks without compromising ‘disease-free’ status, as antibodies induced during infection can be used to distinguish from those induced by vaccination. The potential and feasibility of DIVA vaccination in aquaculture is explored here with reference to DIVA strategies applied in higher vertebrates. Three economically important notifiable viruses, causing major problems in three different cultured fish industries, are considered. The increased availability and application of sophisticated biotechnology tools has enabled improved prophylaxis and serological diagnosis for control of viral haemorrhagic septicaemia in rainbow trout, infectious salmon anaemia in Atlantic salmon and koi herpesvirus disease in carp. Improving the specificity of serological diagnostics in aquaculture in conjunction with suitable vaccines could enable the application of DIVA strategies, but the immunological variation between different fish species and contrasting pathobiological characteristics of different viruses determines the feasibility and potential of such DIVA approaches for aquaculture industries