The expression of selected genes linked to metabolic homeostasis in obese pansteatitis‐suffering Mozambique tilapia, Oreochromis mossambicus (Peters)

Abstract

The Oreochromis mossambicus (Peters) population inhabiting Lake Loskop, South Africa, is characterized by a high incidence of obesity and pansteatitis. We investigated potential links between the impaired health of Lake Loskop O. mossambicus and the endocrine system by assessing the expression of selected genes associated with the thyroid and adrenal endocrine axes as well as peroxisome proliferator-activated receptor gamma (pparg). Moreover, contaminant-induced thyroid and/or metabolic modulation in Lake Loskop water was evaluated using juvenile O. mossambicus in laboratory exposures. The expression of thyroid hormone receptor alpha (thra) and type 2 deiodinase (dio2) was higher in Lake Loskop O. mossambicus than fish from another population, suggesting a degree of thyroid disruption. The altered gene expression may be a consequence, rather than cause of obesity. Expression of dio2 and pparg was higher in juvenile O. mossambicus exposed to unfiltered compared to filtered lake water, and our data suggest fasting as causative factor. Micro-organism abundance can therefore be a confounding factor in studies applying molecular markers to test for thyroid modulation by environmental waters. Pansteatitis was not a significant source of variance in the expression of any of the genes investigated, suggesting that the disease is not associated with disrupted endocrine signalling.

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

“…However, condition factor was not a significant predictor of pansteatitis severity, supporting the findings of Truter et al . () who were unable to link the pansteatitis in Lake Loskop fish to abnormal obesity through hormonal disruption. However, a lack of any relationship between δ 15 N values (as an indicator of trophic level) and size or age does not support the notion of a shift towards piscivory with age as a systematic adaptive strategy of O. mossambicus .…”

An evaluation of the endocrine disruptive potential of crude oil water accommodated fractions and crude oil contaminated surface water to freshwater organisms using in vitro and in vivo approaches

“…Surface water treatments were constantly aerated, but WAF treatments were not. Tadpoles assigned to surface water were fed (∼70 mg of Sera Micron [Sera] per tank) throughout acclimation and exposures, seeing that fasting may alter the expression of thyroid‐linked genes and that the surface water samples likely contained algae and other microorganisms to forage on . The WAF–exposure tadpoles and fish were only fed during the acclimation period.…”

Predictive Blood Chemistry Parameters for Pansteatitis-Affected Mozambique Tilapia (Oreochromis mossambicus)

“…Other portions of the Olifants River system have similarly witnessed massive mortality events of crocodiles and fish. In 2008, approximately 180 adult crocodile carcasses were discovered in the Olifants River Gorge in Kruger National Park (KNP), some 530 km downstream from Lake Loskop, with an estimated number of 500 individual deaths in total [ 2 , 6 , 7 , 10 – 13 ]. The next season (2009), approximately 24 crocodile carcasses were observed in the same area [ 14 ].…”

“…Beyond isolating and connecting specific point source(s) to the large-scale mortality events in the Olifants River system (2003–2010), veterinary examination concluded that the ultimate cause of death in these events was an environmental form of pansteatitis, a disease noted by the presence of inflammation in adipose tissue [ 11 , 14 ]. In addition to crocodile deaths, other species have presented pansteatitis and/or suffered mortality events, including the African sharptooth catfish ( Clarias gariepinus ), Rednose labeo ( Labeo rosae ), Mozambique tilapia ( Oreochromis mossambicus ) and serrated hinged terrapins ( Pelusios sinuatus ) [ 2 , 6 , 10 , 13 , 18 ]. Fish-eating waterfowl species in the Olifants River system have been affected as well; African fish eagles ( Haliaeetus vocifer ) in the Lake Loskop area have struggled to reproduce and cormorant numbers are on the decline [ 5 ].…”

“…Fish exhibited parallel mortality events to the crocodile, are easier to catch, certain species (Mozambique tilapia) are not classified as either endangered or threatened, and therefore present several benefits as a relevant sentinel species in the assessment of newly developed diagnostic assays for pansteatitis. Tilapia were chosen at Lake Loskop due to their relatively robust population and high incidence of pansteatitis [ 2 , 8 ].…”