New record of parasitic isopod (Isopoda: Bopyridae) infecting the branchial chamber of blue swimming crab Portunus pelagicus (Linnaeus, 1758) (Decapoda: Portunidae) in the Philippines

A parasitic disease causing swollen carapace in commercially important blue swimming crab (Portunus pelagicus L.) has not received considerable attention; neither its causative agent is identified nor its seasonality is recorded. This study aimed to identify the parasite in P. pelagicus inhabiting the Manila Bay. Parasite found in the branchial chamber were isolated, preserved in ethanol and examined. A total of 292 crab specimens were examined and ten were found to be infected (3.42% prevalence with 0–2 parasites per host). Infections were only observed in November 2014 and between January and June 2015. The highest prevalence of infection (10.34%) was recorded in January 2015 whereas the greatest intensity of infection (up to two parasites per infected crab individual) was recorded from February to April 2015. The parasite, based on morphology, was identified as Allokepon monodi. This study presents the third record of female and second record of male A. monodi infecting a crab species. It also represents the first record of male A. monodi in P. pelagicus and in the Philippines. We recommend further studies on the impacts and economic implications of the disease.