Steatitis in wild sharptooth catfish, Clarias gariepinus (Burchell), in the Olifants and lower Letaba Rivers in the Kruger National Park, South Africa

Ontogenetic dependence of Nile crocodile (Crocodylus niloticus) isotope diet-to-tissue discrimination factors

RATIONALE

The diet of wild Nile crocodiles (Crocodylus niloticus) is difficult to assess because they are cryptic and nocturnal predators that are extremely sensitive to disturbance by observers, and stomach content analysis is challenging, especially in large specimens. Stable light isotope analysis provides a means of assessing their diet, but diet-to-tissue discrimination factors have yet to be established for the species.

METHODS

Isotope ratio (¹⁵ N/¹⁴ N and ¹³ C/¹² C expressed as δ¹⁵ N and δ¹³ C) analyses of scutes, claws, and blood of farmed crocodiles of different sizes were compared with the isotope values of their lifelong diet, which comprises chickens from a single supplier.

RESULTS

Systematic size dependence in the diet-to-tissue discrimination factors for scute collagen, scute keratin, and claw keratin is described in regression relationships against the snout to vent length. Fixed values are presented for erythrocytes and blood plasma because blood was not sampled from juveniles.

CONCLUSIONS

The diet-to-tissue discrimination factors help assess the diet of wild crocodiles. The diet of crocodiles from Lake Flag Boshielo shows a clear ontogenic shift, as has been seen in other studies, and the results strongly indicate a dependence on the terrestrial food web rather than a fish diet. That this population may exploit a terrestrial diet highlights potential conflicts for conserving Nile crocodiles outside protected areas.

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

Pansteatitis is the leading cause for the decline in Nile crocodile populations and the sporadic mortality of fish in the Olifants River System, South Africa. To determine the prevalence of this disease in lentic systems, Mozambique tilapia, Oreochromis mossambicus, were collected from Lake Loskop, Lake Flag Boshielo, Phalaborwa Barrage and Lake Luphephe-Nwanedi. The former three impoundments are located within the main stem of the Olifants River, while the latter, which is geographically isolated and situated in the Limpopo River System, served as a reference site. Mesenteric adipose, liver, serosa of the swim bladder, gill and the skeletal muscle of fish sampled were examined for gross and microscopic evidence of pansteatitis. Microscopically observed changes were used to statistically compare pansteatitis prevalence between samples and sites. Based on histopathological evaluation, the adipose tissue in the liver, swim bladder serosa and coelom from severely debilitated individuals showed the most significant pathological changes. Lesions indicative of steatitis were observed in fish collected from Lake Loskop (75%), Lake Flag Boshielo (22%) and Lake Luphephe-Nwanedi (15%). Further investigation is warranted to understand the pervasiveness and mechanisms driving pathological changes of pansteatitis at Lake Flag Boshielo, Phalaborwa Barrage and Lake Luphephe-Nwanedi.

Lipidomics for wildlife disease etiology and biomarker discovery: a case study of pansteatitis outbreak in South Africa

INTRODUCTION

Lipidomics is an emerging field with great promise for biomarker and mechanistic studies due to lipids diverse biological roles. Clinical research applying lipidomics is drastically increasing, with research methods and tools developed for clinical applications equally promising for wildlife studies.

OBJECTIVES

Limited research to date has applied lipidomics, especially of the intact lipidome, to wildlife studies. Therefore, we examine the application of lipidomics for in situ studies on Mozambique tilapia (Oreochromis mossambicus) in Loskop Dam, South Africa. Wide-scale mortality events of aquatic life associated with an environmentally-derived inflammatory disease, pansteatitis, have occurred in this area.

METHODS

The lipidome of adipose tissue (n = 31) and plasma (n = 51) from tilapia collected from Loskop Dam were characterized using state of the art liquid chromatography coupled to high-resolution tandem mass spectrometry.

RESULTS

Lipid profiles reflected pansteatitis severity and were significantly different between diseased and healthy individuals. Over 13 classes of lipids associated with inflammation, cell death, and/or oxidative damage were upregulated in pansteatitis-affected adipose tissue, including ether-lipids, short-chained triglyceride oxidation products, sphingolipids, and acylcarnitines. Ceramides showed a 1000-fold increase in the most affected adipose tissues and were sensitive to disease severity. In plasma, triglycerides were found to be downregulated in pansteatitis-affected tilapia.

CONCLUSION

Intact lipidomics provided useful mechanistic data and possible biomarkers of pansteatitis. Lipids pointed to upregulated inflammatory pathways, and ceramides serve as promising biomarker candidates for pansteatitis. As comprehensive coverage of the lipidome aids in the elucidation of possible disease mechanisms, application of lipidomics could be applied to the understanding of other environmentally-derived inflammatory conditions, such as those caused by obesogens.

Biomarkers in tigerfish (Hydrocynus vittatus) as indicators of metal and organic pollution in ecologically sensitive subtropical rivers

Studies have shown high levels of contamination of both metals and organochlorine pesticides (OCPs) in aquatic systems of the world renowned Kruger National Park, South Africa. With effects evident in top predators, including, unexplained Crocodylus niloticus deaths and organ level and histological changes in Hydrocynus vittatus. A suite of biomarkers reflecting exposure and were selected to evaluate biological responses of H. vittatus to anthropogenic stressors as well as to evaluate whether the chosen suite of biomarkers could successfully distinguish between the different pollution profiles present in the selected rivers. During this study a clear relationship was found between exposure to environmental contaminants and the concomitant responses of H. vittatus to these stressors. The ensuing biomarker responses indicated that there is a physiological attempt to deal with, and mitigate the deleterious effects that metals and OCPs may induce. In the Luvuvhu River there is a clear indication in H. vittatus of the stimulation of anti-oxidant protective mechanisms in response to internal OCP exposure. This is reflected by the increasing cytochrome P-450, superoxide dismutase, and more specifically reduced glutathione, which resulted in decreased lipid and protein breakdown (reflected in decreased lipid peroxidation and protein carbonyl levels). Consequently H. vittatus populations of the Luvuvhu River are under greater cumulative stress and this is reflected in the lower energy budgets. Our results further show the integrated application value of the current suite of biomarkers in assessing responses of subtropical fish to metal and OCP exposure as the entire suite of biomarkers when used in conjunction were able to explain 100% of the variation in the data.

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

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.

Thyroid function of steatitis-affected Mozambique tilapia Oreochromis mossambicus from a sub-tropical African reservoir

Thyroid function and nutritional indicators were measured in obese, steatitis-affected Mozambique tilapia Oreochromis mossambicus from Loskop Reservoir (LR), South Africa. Plasma thyroid hormones (especially T3) and thyroid follicle histomorphology revealed high levels of activity in every aspect of the thyroid cascade measured in fish from LR compared to a reference population of steatitis-free fish. Concurrent measurements of nutritional state including plasma lipids, liver lipid content and hepatocyte size showed that fish from LR had significant energy stores indicative of abundant nutritional intake. There were distinct sex and seasonal differences, with the highest plasma lipids and T3 levels observed in steatitis-affected females during spring and summer. Positive correlations were observed between plasma lipids (especially cholesterol) and T3 concentrations in fish from both populations, indicating a link between lipid metabolism and thyroid function. There was no direct evidence of thyroid disruption, but this cannot be ruled out until further research determines the factors that underlie the homeostatic shift leading to elevated plasma and liver lipids and T3 levels in steatitis-affected tilapia.

Perfluorinated alkyl acids in the plasma of South African crocodiles (Crocodylus niloticus)

Perfluorinated alkyl acids (PFAAs) are environmental contaminants that have been used in many products for over 50 years. Interest and concern has grown since 2000 on the widespread presence of PFAAs, when it was discovered that PFAAs were present in wildlife samples around the northern hemisphere. Since then, several studies have reported PFAAs in wildlife from many locations, including the remote regions of Antarctica and the Arctic. Although there are a multitude of studies, few have reported PFAA concentrations in reptiles and wildlife in the Southern Hemisphere. This study investigated the presence of PFAAs in the plasma of Nile crocodiles (Crocodylus niloticus) from South Africa. Crocodiles were captured from five sites in and around the Kruger National Park, South Africa, and plasma samples examined for PFAAs. Perfluorooctane sulfonate (PFOS) was the most frequent PFAA detected; with median values of 13.5 ng/g wet mass in crocodiles. In addition to PFOS, long chain perfluorinated carboxylic acids were also detected. Correlations between total length and PFAA load were investigated, as were differences in PFAA accumulation between sexes. No correlations were seen between crocodile size, nor were there sex-related differences. Spatial differences were examined and significant differences were observed in samples collected from the different sites (p < 0.05). Flag Boshielo Dam had the highest PFOS measurements, with a median concentration of 50.3 ng/g wet mass, when compared to the other sites (median concentrations at other sites below 14.0 ng/g wet mass). This suggests a point source of PFOS in this area.

On-Site Classification of Pansteatitis in Mozambique Tilapia (Oreochromis mossambicus) using a Portable Lipid-Based Analyzer

While no pansteatitis-related large-scale mortality events have occurred since 2008, the current status of pansteatitis (presence and pervasiveness) in the Olifants River system and other regions of South Africa remain largely unknown. In part, this is due to both a lack of known biological markers of pansteatitis and a lack of suitable non-invasive assays capable of rapidly classifying the disease. Here, we propose the application of a point-of-care (POC) device using lipid-based test strips (total cholesterol (TC) and total triglyceride (TG)), for classifying pansteatitis status in the whole blood of pre-spawning Mozambique tilapia (Oreochromis mossambicus). Using the TC strips, the POC device was able to non-lethally classify the tilapia as either healthy or pansteatitis-affected; the sexes were examined independently because sexual dimorphism was observed for TC (males p = 0.0364, females χ2 = 0.0007). No significant difference between diseased and pansteatitis-affected tilapia was observed using the TG strips. This is one of the first described applications of using POC devices for on-site environmental disease state testing. A discussion on the merits of using portable lipid-based analyzers as an in-field disease-state diagnostic tool is provided.

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

One of the largest river systems in South Africa, the Olifants River, has experienced significant changes in water quality due to anthropogenic activities. Since 2005, there have been various “outbreaks” of the inflammatory disease pansteatitis in several vertebrate species. Large-scale pansteatitis-related mortality events have decimated the crocodile population at Lake Loskop and decreased the population at Kruger National Park. Most pansteatitis-related diagnoses within the region are conducted post-mortem by either gross pathology or histology. The application of a non-lethal approach to assess the prevalence and pervasiveness of pansteatitis in the Olifants River region would be of great importance for the development of a management plan for this disease. In this study, several plasma-based biomarkers accurately classified pansteatitis in Mozambique tilapia (Oreochromis mossambicus) collected from Lake Loskop using a commercially available benchtop blood chemistry analyzer combined with data interpretation via artificial neural network analysis. According to the model, four blood chemistry parameters (calcium, sodium, total protein and albumin), in combination with total length, diagnose pansteatitis to a predictive accuracy of 92 percent. In addition, several morphometric traits (total length, age, weight) were also associated with pansteatitis. On-going research will focus on further evaluating the use of blood chemistry to classify pansteatitis across different species, trophic levels, and within different sites along the Olifants River.

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

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.

Splenic lipidosis in intensively cultured perch, Perca fluviatilis L

Macroscopically visible lipid deposition varying in size from pinpoint to 8-mm diameter was found in spleens of a population of intensively farmed perch, Perca fluviatilis L. over a 24-month rearing period. Large agglomerates of adipocytes distinguishable from surrounding normal tissue occurred in all individuals with spleen lipidosis. Several affected fish presented total dystrophy of large clusters of hepatocytes. Prevalence of lipidosis was 5.0% at 12 months and 16.6% at 24 months. There was no significant difference between fatty acid profiles of liver or perivisceral fat of perch with and without lipidosis except for linoleic, myristic, γ-linoleic, cis-eicosatrienic, palmitooleic acid. Body weight and hepatosomatic, perivisceral fat and splenosomatic indices were not associated with lipidosis. There was no significant effect of lipidosis on mortality or growth.

Chlorinated, brominated, and fluorinated organic pollutants in Nile crocodile eggs from the Kruger National Park, South Africa

Repeated annual episodes of Nile crocodile deaths in two isolated areas of the Kruger National Park prompted the investigation of possible organohalogen pollutant involvement. Crocodile eggs were collected close to one of the mortality sites (Gorge) as well as from a crocodile farm (CF) as reference. ∑DDT was significantly higher in Gorge (450ng/g wm) than in CF eggs (85ng/g wet mass). Percentage DDT of ∑DDT was significantly higher in CF (14 per cent) than in Gorge eggs (5 per cent). Mean ∑DDT was almost 70 times higher than mean ∑PCB in Gorge eggs. HCB, β-HCH, mirex, brominated flame retardants (BFRs), and perfluorinated compounds (PFCs) occurred at lower concentrations. We believe that the BFR and PFCs data represent the first published results for any crocodile egg. Thickening of the outer eggshell layer of Gorge eggs was significantly associated with higher concentrations of ∑DDT. Concentrations of ∑DDT and other pollutants were in the same range as eggs from elsewhere, where there were no mortalities. Concentrations of ∑DDT in eggs from healthy Australian crocodiles were of the same orders of magnitude as the current study, making it highly unlikely that the concentrations of pollutants measured in the present study would have caused or substantially contributed towards the mortalities observed. Concerns about reproduction and behaviour remain. As large predators, crocodilians are at the apex of the freshwater aquatic food web. More research is needed to guide measures to manage African freshwater systems so that it will also sustainably accommodate these large, long-lived animals.

Comparison of the lipid properties of healthy and pansteatitis-affected African sharptooth catfish, Clarias gariepinus (Burchell), and the role of diet in pansteatitis outbreaks in the Olifants River in the Kruger National Park, South Africa

Pansteatitis has been identified in wild populations of sharptooth catfish, Clarias gariepinus (Burchell), and Nile crocodiles, Crocodylus niloticus Laurenti, inhabiting the same waters in the Olifants River Gorge in the Kruger National Park, South Africa. Mesenteric and pectoral fat tissue was investigated microscopically and by fatty acid analysis in healthy and pansteatitis-affected catfish from both captive and wild populations. Variation in fatty acid composition between pectoral and mesenteric fat was noted. Composition of mesenteric fat differed between fish from various localities as a result of differences in diet. Pansteatitis in the captive population, resulting from ingestion of high amounts of dietary oxidized fat, reflected higher levels of unsaturated fatty acids within the mesenteric fat. Mesenteric fat of pansteatitis-affected wild catfish was characterized by an increase in moisture content, a decrease in fat content and a decrease in stearic and linoleic acids. The n-3 to n-6 fatty acid ratio of mesenteric fat was higher in pansteatitis-affected wild catfish than in healthy catfish from the same locality, reflecting higher polyunsaturated fat intake by pansteatitis-affected fish. The possible role of alien, invasive, phytoplankton-feeding silver carp, Hypophthalmichthys molitrix (Valenciennes), in the aetiology of pansteatitis in both catfish and crocodiles in the Olifants Gorge is discussed.

Pansteatitis associated with high levels of polychlorinated biphenyls in a wild loggerhead sea turtle Caretta caretta

We describe the morphologic and toxicological findings in a case of pansteatitis in a stranded loggerhead sea turtle Caretta caretta. At necropsy, a large amount of adipose tissue in the celomic cavity showing very firm, yellow to orange irregular formations was observed. Histological lesions ranged from the infiltration of necrotic fat by scarce multinucleated giant cells and numerous macrophages containing xylene-insoluble lipopigment inclusions to the presence of several granulomas characterized by an irregular central necrotic area consisting of lipopigment surrounded by numerous multinucleated giant cells. Microbiological cultures were negative. Celomic fat was analyzed for PCBs and DDTs, resulting in very high levels of PCB 138, 153, 180 209 (3170, 2830, 980 and 1190 ng g-1, respectively). Although a nutritional cause cannot be ruled out, the high levels of PCBs detected in the celomic fat could have induced lipid peroxidation in adipocytes, resulting in cell damage, deposition of ceroid pigment and inflammatory response. This is the first report of pansteatitis in a wild sea turtle.

Prevalence of pansteatitis in African sharptooth catfish, Clarias gariepinus (Burchell), in the Kruger National Park, South Africa

Pansteatitis was confirmed in sharptooth catfish, Clarias gariepinus (Burchell), from three main locations within the Kruger National Park (KNP); the Olifants River Gorge, Engelhard Dam on the Letaba River and from the Sabie River in the Sabiepoort. An increasing prevalence of pansteatitis was observed in catfish during repeated samplings from the Olifants Gorge from 2009 to 2011 and co-existence of old and recent lesions indicated on-going incitement of pansteatitis. Only a low prevalence of pansteatitis was observed in catfish sampled from the Olifants River upstream of the Gorge in the KNP and no pansteatitis was observed in catfish sampled from a rain-filled dam not connected to the Olifants River. Common to both the Olifants Gorge and the Sabiepoort is the damming of the rivers in Mozambique to form lakes Massingir and Corumana respectively. Anthropogenic activities resulting in potential pollution of the rivers differ greatly between these two catchments, providing argument against a primary pollution-related aetiology of the pansteatitis found at these two sites. Compared with other sites, analysis of stomach contents of catfish from the Olifants Gorge and the Sabiepoort strongly suggested that consumption of a predominantly fish diet was associated with the development of pansteatitis in these fish. In a farmed population of catfish used as positive control, development of pansteatitis could be ascribed to consumption of rancid fish waste from a trout slaughterhouse. In the Olifants Gorge, alien invasive silver carp, Hypophthalmychthys molitrix (Valenciennes), seasonally migrate upstream out of Lake Massingir to spawn. This schooling species is an obligate phytoplankton feeder with consequent high levels of adipose tissue n-3 polyunsaturated fatty acids. In the Olifants Gorge, at least, this may explain seasonal exposure to levels of polyunsaturated fats in the diets of catfish and crocodiles to which these animals are not adapted. The possible roles of diet, membrane lipid composition and metabolic rate of fish, sediment pollution and seasonal drop in environmental temperature in the pathogenesis of pansteatitis in the catfish are discussed. Further studies are needed to verify some of these speculations.

Xanthogranulomatous panniculitis of the head of an aquarium-maintained California moray

An aquarium-maintained male California moray Gymnothorax mordax had a symmetrical enlargement of the soft tissues of the head dorsal to the cranium for 2 years prior to its death. This individual was anesthetized for radiographic and ultrasonographic examination of the lesion, and blood was collected for plasma biochemical analytes and lipid profiles. Radiographs and ultrasound of the lesion demonstrated a symmetrical and homogeneous soft tissue density that was consistent with adipose tissue. Plasma cholesterol and triglyceride values appeared elevated; therefore, the animal's diet was amended to decrease fat consumption. Triglyceride values decreased after dietary changes were made; however, values for cholesterol, high-density lipoproteins, and low-density lipoproteins fluctuated but remained largely unchanged. Histopathological assessment of the lesion revealed localized xanthogranulomatous inflammation of hypodermal adipose tissue. The etiology of the lesion in this animal was never determined. This paper describes the first documented case of localized xanthogranulomatous panniculitis in a California moray and demonstrates the need for additional research on specific dietary requirements, species-specific physiological differences, and lesions involving the adipose tissue of morays in comparison with other teleost species.