Biomarker responses, bioaccumulation and edibility risks in African sharptooth catfish treated with ionic and nano silver for monogenean control

Title : Biomarker responses, bioaccumulation and edibility risks in African sharptooth catfish treated with ionic and nano silver for monogenean control

Abstract:

Infections by the monogenean ectoparasite Macrogyrodactylus congolensis can become a major health problem in Clarias gariepinus in aquaculture, where heavy parasite loads compromise gill and skin integrity, thereby impacting osmoregulation and ultimately reducing growth and survival. In the University of Johannesburg aquarium, M. congolensis was accidentally introduced into the system and present in low numbers, but it rapidly increased. Parasites spread through recirculating systems, leading to a widespread infection which could not be controlled with routine husbandry and conventional treatments. Thus, alternative control strategies that will eradicate the parasite, but are still safe for the fish, were considered. Silver-based treatments have been proposed as an alternative; however, little understanding of the host's reactions and consumer safety was available. Therefore, the current study aims to evaluate the biomarker responses of C. gariepinus infected with M. congolensis exposed to sublethal concentrations of AgNO₃ and nAg, focusing on organ-specific bioaccumulation and edibility. Fish were exposed to LC₁₀ concentrations of AgNO₃ and nAg of the parasite for 10 days. Thereafter, the gill, liver, muscle, intestine and brain tissues were collected from each fish for biomarker (AChE, MT, SOD, CAT and GSH) analysis using standard protocols. The bioaccumulation in each organ was measured using ICP-MS.  The AChE activity increased with exposure to nAg, whereas exposure to AgNO₃ did not significantly differ from the control. MT concentrations were comparable across groups, with an increase in the intestinal tissue of fish exposed to AgNO₃. The SOD concentrations were lower than those seen in the control, while CAT activity in the liver tissue was only increased with exposure to AgNO₃. GSH concentrations decreased in the gill, liver, muscle and brain tissues in both silver treatments and increased in the intestinal tissue with nAg exposure. These biomarker responses showed no difference between fish infected with M. congolensis and uninfected fish and correlated with tissue-specific bioaccumulation concentrations, showing organ susceptibilities and highlighting human consumption health risks associated with fish treated with silver.

Biography:

Lutfiyya Latief is a PhD candidate in the Zoology department at the University of Johannesburg, South Africa, specialising in Aquatic Fish Parasitology and toxicology resulting from treatment. Her research focuses on the uses and impacts of ionic silver and nano silver on the African sharptooth catfish (Clarias gariepinus) and its monogenean parasite (Macrogyrodactylus congolensis).