The use of liver histopathology, lipid peroxidation and acetylcholinesterase assays as biomarkers of contaminant-induced stress in the Cape stumpnose, <i>Rhabdosargus holubi</i> (Teleostei: Sparidae), from selected South African estuaries

Abstract

Three biomarkers of contaminant-induced stress (liver histopathology, the lipid peroxidation (LPx) assay and the acetyl-cholinesterase (AChE) assay) were adapted for application to the estuarine-dependent marine fish Rhabdosargus holubi (Steindachner, 1881). Specimens of R. holubi were collected using a seine net from 3 temporarily open/closed estuaries in the Eastern Cape, South Africa, each impacted by different anthropogenic activities. The East Kleinemonde estuary has a housing settlement on the banks in the lower reaches and some agriculture in its catchment. The Old Woman's estuary has a golf course adjacent to its lower and middle reaches and is crossed by a national road in its upper reaches. The Mtana estuary is virtually pristine, with limited cattle grazing occurring along the banks of the estuary and some subsistence agriculture in the catchment. According to the biomarker results from this study, R. holubi from the East Kleinemonde were in good health, as reflected by low LPx and high AChE levels. The liver histopathology did, however, suggest possible previous exposure to stress (increased melanomacrophage centres, increased perivascular connective tissue and severe vacuolation). Overall, liver histopathology results did not differ significantly between estuaries. Fish from the Old Womans recorded significantly inhibited AChE and increased LPx, while fish from the Mtana exhibited significantly increased LPx only, suggesting possible exposure to anticholinesterase contaminants in the former estuary and some form of oxidative stress in the latter. Although water samples were collected from each of the 3 estuaries and analysed for polychlorinated biphenyls, organochlorines, organophosphorous pesticides and pyrethroids, none of these chemicals were detected. As pesticide residues in water are highly variable, both temporally and spatially, future studies should focus on measuring tissue burdens of organisms in order to identify the contaminant stressor. This study has shown that while chemical analyses of water provide a 'snap-shot' of water quality at the time of sampling, biomonitoring can integrate past exposures to stress and is thus useful for identifying potential situations of concern that require further detailed investigation.

A weight‐of‐evidence approach to determine estuarine fish health using indicators from multiple levels of biological organization

“…As discussed in more detail by Richardson et al (), R. holubi from the East Kleinemonde Estuary appeared in good health, as reflected by low LPx and high AChE levels. The liver histopathology did, however, suggest possible previous exposure to stress in the case of certain fish.…”

“…Results from the different field biomarkers investigated provided conflicting evidence of R. holubi stress exposure from the three estuaries (Table ) and are discussed in greater detail by (Richardson et al , ). Significantly lower levels of AChE were found in R. holubi inhabiting the Old Woman's compared with the other two estuaries ( P < 0.001), suggesting the possible presence of AChE inhibiting chemicals (e.g.…”

“…At the time of sampling, the mouths of all three estuaries had been closed by a sandbar for approximately four months, thereby ensuring that the fish sampled in a particular estuary had been exposed to the conditions in that estuary for at least that period. The estuaries differ according to the types of human impacts occurring within their catchments (Richardson et al , ). In the East Kleinemonde catchment, housing developments occur along the banks of the lower estuary reaches while pineapple and cattle farms occur in the upper catchment area.…”

“…Liver histopathological analyses were also undertaken on R. holubi to provide an indication of the organ level health of a sample of fish from each estuary. The methodology used in the LPx, AChE and liver histopathology assays, and detailed results obtained, are described in (Richardson et al , ). None of the biomarker data were normally distributed (STATISTICA TM version 7 was used for all data analyses) and consequently results are presented as medians with 95% confidence intervals.…”

“…The brain and liver were immediately excised, snap frozen in liquid nitrogen and stored at −80 °C until further analysis. Methods for determining LPx levels and AChE activity are described in (Richardson et al , ). AChE results are presented in nmol min −1 mg −1 protein and LPx results as nmol MDA formed h −1 mg −1 protein.…”