Abstract
Infestation of Sacculina beauforti on an aquaculture species, mud crab Scylla olivacea is alarming due to its high prevalence and the extreme morphological changes in hosts. To further understand its pathological effect on growth and reproduction of S. olivacea, gonadal and hepatopancreatic histological changes of infected individuals were compared with healthy individuals. Also, the histological characteristics of S. beauforti's mature externa was described. Hepatopancreases of infected individuals were loosely packed and rootlets were observed in the intertubular spaces. Although hepatopancreatic tubule count was significantly lower, tubule diameters were unaffected. Gonads, however, were severely affected. No germ cells were found in the infected testes (except for remnants of spermatozoa), indicating the arrest of spermatogenesis. Rootlets were also present in testes of infected individuals. Ovarian tissues of infected females were severely damaged with no rigid cell structures. Gonadosomatic index (GSI) of infected males and females were lower, but the hepatosomatic index (HSI) were higher than their healthy counterparts. No significant differences in GSI and HSI values were observed among infected males and females. Multiple regression analysis revealed that carapace width, GSI and HSI are statistically important for the prediction of infection status. Given the high prevalence of S. beauforti infection and its disruptive effects on the morphology and internal physiology of S. olivacea, this study, albeit fundamental and incomprehensive, highlights to farmers and researchers the emergence of a castrating parasite and the urgency for the development of preventive measures and treatments for this disease in an economically important aquaculture species.
Highlights
Orange mud crab Scylla olivacea is widely distributed around Southeast Asia (SEA) countries, Australia, Japan and Pakistan (Keenan et al, 1998; Alberts-Hubatsch et al, 2016)
As the growth and reproduction of crustaceans are primarily regulated by hepatopancreas and gonads (Wang et al, 2014), we investigated the pathological changes of the S. beauforti infection had on these two organs of S. olivacea
A cuticle clad mantle cavity is located between the mantle cavity and the mantle, and it communicates with the surrounding seawater by a mantle opening
Summary
Orange mud crab Scylla olivacea is widely distributed around Southeast Asia (SEA) countries, Australia, Japan and Pakistan (Keenan et al, 1998; Alberts-Hubatsch et al, 2016). According to FAO (2019), the global aquaculture production of mud crabs (Scylla spp.) was doubled within 3 years, from 41,460 tons in 2013 to 89,390 tons in 2016. The aquaculture production of mud crabs, still relies almost entirely on wild-caught seeds and broodstocks (Waiho et al, 2018). In most countries including Malaysia where wild population of mud crabs are still abundant, most aquaculture activities involve fattening and soft-shell crab farming using juveniles. They are often held in earthen ponds that rely on spring tide for water exchange or directly cultured in pens and cages in their natural environment (mangroves, lagoons or estuarine areas) (Ihwan et al, 2013). Industrial players and research institutions are working toward optimization of mud crab larval rearing, broodstocks are still sourced from the wild (Waiho et al, 2018)
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