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

Abstract

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.

Low levels of crustacean parasite infestation in fish species from the Matapi River in the state of Amapá, Brazil

“…Oliveira et al (2017) reported that in 13 host species of the Jari River (state of Amapá), the prevalence of parasites was 63.8%; they collected 399 parasite specimens. However, the diversity of crustacean parasites and their levels of infestation can be influenced by various factors relating to the biology of parasites and hosts, and by environmental factors, among others (CARVALHO et al, 2003;MAMANI et al, 2004;FONTANA et al, 2012;ALSARAKIBI et al, 2014;MIKHEEV et al, 2015;VASCONCELOS & TAVARES-DIAS, 2016). Fish hosts may be are used by these parasites for transportation (CARVALHO et al, 2003), which could be facilitated by migrating fish species.…”

“…Fish hosts may be are used by these parasites for transportation (CARVALHO et al, 2003), which could be facilitated by migrating fish species. However, this low prevalence of parasites in the hosts of the Matapi River may be due to the influence of daily tides from the Amazon River, considering that certain crustacean parasites respond to water movement to reach their hosts (MIKHEEV et al, 2015).…”

“…Moreover, with time, the hosts' stress increases and their metabolism tends to decrease, which could stimulate these ectoparasites in the tegument of the fish to explore new habitats for their survival (BRANDÃO et al, 2013). Another factor that needs to be considered is the strong influence of diary tides from the Amazon River on the velocity of the Matapi River (CUNHA et al, 2011;SILVA et al, 2016), given that these parasites need to swim to find adequate hosts, while others depend on the flow of water and swimming speed (FONTANA et al, 2012;MIKHEEV et al, 2015).…”

Argulus from the Pascagoula River, MS, USA, with an Emphasis on Those of the Threatened Gulf Sturgeon, Acipenser oxyrinchus desotoi

“…Argulids are free swimming ectoparasites that must swim to attach to a host; therefore, a bigger fish presumably offers a larger target for attachment. Additionally, bigger fish produce larger wakes than small fish [51] that may decrease water flow around them thereby reducing the risk of the parasite being distributed downstream [52]. The water of the Pascagoula River is also very turbid and a bigger fish would also cast a larger shadow than a smaller fish that may help A. flavescens ambush it during daylight hours [53].…”

“…For much of the Fall of 2017 the Pascagoula River experienced increased flow relative to 2016, 2018, and 2019. This resulted in fewer Gulf sturgeon captured, but could have also prevented A. flavescens from finding and attaching to Gulf sturgeon since the increased flow may have dispersed the parasites downstream or made swimming more difficult [52].…”