Pansteatitis in polluted Olifants River impoundments: nutritional perspectives on fish in a eutrophic lake, Lake Loskop, South Africa

Abstract

This study compares the aetiology of pansteatitis in Lake Loskop, relative to two other impoundments along the Olifants River. Macroscopic and microscopic pathology, age determination and analysis of stomach content, fatty acids and stable isotopes explain the high prevalence of pansteatitis in Oreochromis mossambicus (Peters) and several other species in Lake Loskop. All the dietary indicator comparisons between pansteatitis-affected and healthy fish fail to support a systemic cause. Pansteatitis in Lake Loskop was linked to size and weight of O. mossambicus, but not to ontogenic age. Fish in Lake Loskop showed abnormally high omega-3 to omega-6 fatty acid ratios normally only found in marine fish with no significant difference in degree of assimilation of these fatty acids between pansteatitis-affected and healthy fish. This explains the vulnerability to, but not the occurrence of, pansteatitis. As a cause for the pansteatitis, these results point towards sporadic vitamin E-depleting trigger events, known sporadic fish die-off occurrences that provide surviving fish with a rich source of rancid fats on which to scavenge. The mechanism ties pansteatitis to eutrophication and trophic cascade effects, the intrinsic drivers of the disease and suggests an adaptive management strategy that might be applied by relevant conservation authorities.

A histological evaluation of pansteatitis‐affected Mozambique tilapia, Oreochromis mossambicus (Peters 1852), from different geographical locations in South Africa

“…Over the past two decades, seemingly random large‐scale mortality events of the Nile crocodile ( Crocodylus niloticus Laurenti, 1768) have occurred in lotic and lentic systems along the Olifants River, South Africa (Ashton, 2010; Ferreira & Pienaar, 2011; Huchzermeyer et al., 2017). Veterinary investigations have characterized these events as an environmental form of pansteatitis.…”

“…Veterinary investigations have characterized these events as an environmental form of pansteatitis. In addition to crocodiles, this disease has been documented in the serrated hinged terrapin Pelusios sinuatus (Smith, 1838) (Huchzermeyer, Govender, Pienaar, & Deacon, 2011; Oberholster, Myburgh, Ashton, Coetzee, & Botha, 2012), fish species such as the African sharptooth catfish ( Clarias gariepinus (Burchell, 1822), the rednose labeo ( Labeo rosae Steindachner, 1894)), the Mozambique tilapia ( Oreochromis mossambicus (Peters, 1852))(Huchzermeyer, 2012a; Huchzermeyer et al., 2011, 2017; Huchzermeyer, Osthoff, Hugo, & Govender, 2013; Truter, Wyk, Oberholster, Botha, & Luus‐Powell, 2014) and various piscivorous birds (Myburgh & Botha, 2009; Oberholster, 2009) inhabiting the Olifants River System. Clinicopathological manifestation of pansteatitis includes adipose tissue necrosis, histiocytic inflammation and ceroid accumulation within granulomata and cytoplasm of aggregated macrophages, with severe cases resulting in the immobility and death of the affected host (Bangma et al., 2017; Huchzermeyer, 2012a, 2012b; Myburgh & Botha, 2009; Orós, Monagas, Calabuig, Luzardo, & Camacho, 2013).…”

“…Clinicopathological manifestation of pansteatitis includes adipose tissue necrosis, histiocytic inflammation and ceroid accumulation within granulomata and cytoplasm of aggregated macrophages, with severe cases resulting in the immobility and death of the affected host (Bangma et al., 2017; Huchzermeyer, 2012a, 2012b; Myburgh & Botha, 2009; Orós, Monagas, Calabuig, Luzardo, & Camacho, 2013). Environmental forms of pansteatitis have been linked to deleterious water conditions in conjunction with a deficiency in plasma vitamin E (Huchzermeyer, 2012a, 2012b; Huchzermeyer et al., 2013, 2017; Lane et al., 2013), selenium (Huchzermeyer, 2012a; Lane et al., 2013) and nutritional deficiencies associated with the ingestion and metabolism of large quantities of polyunsaturated lipids under oxidative conditions (Huchzermeyer et al., 2017).…”

“…A confounding feature of pansteatitis‐related deaths is the heterogeneous distribution of the disease throughout the Olifants River System (Bangma et al., 2017; Huchzermeyer et al., 2017). Currently, there are no reports available that highlight the prevalence and severity of pansteatitis in fish species within the Olifants River System.…”

“…More information is critically needed to characterize the disease in the system (Bowden, Cantu, et al, 2016). To establish the aetiology of the disease, the pathology of various body tissues has been examined in pansteatitis‐affected African sharptooth catfish (Huchzermeyer et al., 2017) and Mozambique tilapia (Bangma et al., 2017; Bowden, Cantu, et al, 2016; Bowden, Somerville, et al, 2016; Dabrowski et al., 2017; Truter et al., 2014) from Lake Loskop and sharptooth catfish from waterbodies in close proximity to and within the KNP (Huchzermeyer, 2012a, 2012b; Huchzermeyer et al., 2011, 2013, 2017). Besides research by Huchzermeyer (2012a, 2012b) and Huchzermeyer et al.…”