Histopathological observations on liver, kidney and gonad of plaice (Pleuronectes platessa) taken from the Mersey estuary

Histopathological observations on liver, kidney and gonad of plaice (Pleuronectes platessa) taken from the Mersey estuary

Marine Environmental Research 54 (2002) 543–546 www.elsevier.com/locate/marenvrev Histopathological observations on liver, kidney and gonad of plaice...

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Marine Environmental Research 54 (2002) 543–546 www.elsevier.com/locate/marenvrev

Histopathological observations on liver, kidney and gonad of plaice (Pleuronectes platessa) taken from the Mersey estuary Michael G. Simpson*, Peter Walker, Alison Helm, Rick Leah University of Liverpool, Environmental Research and Consultancy (Centre for Marine and Coastal Studies), Vanguard Way, Birkenhead, Merseyside CH41 9HX, UK

Abstract The Mersey estuary is the most contaminated estuary in British waters. Detailed studies are underway on the pathology of flounder (Platichthys flesus) from the Mersey and on flounder from the nearby, but less contaminated, Dee estuary. Flounder breed offshore but spend a lot of time in the estuaries, penetrating into freshwater. These flatfish are in close contact with sediments and will be exposed to exenobiotic stored in the sediments. Plaice (Pleuronectes platessa) are flatfish which enter the Mersey with the tidal flow but spend less time in the estuary than flounder and are less likely to show evidence of pollutant exposure. Over 20 plaice were collected from the Mersey. Samples of the liver, kidney and gonad were fixed in 10% formal saline, processed into paraffin wax and 5 mm sections cut and stained with haematoxylin and eosin. Liver changes consisted of variable amounts of glycogen/lipid storage product, minor perivenular and perivascular fibrosis, and helminth parasitisation. No tumours or foci of cellular alteration, necrosis and inflammation were seen. In the gonad only changes consistent with normal gonadal cycling was seen. These studies provide evidence that plaice show little or no evidence of toxic pathological damage resulting from their stay in the estuary. # 2002 Elsevier Science Ltd. All rights reserved. Keywords: Histopathology; Pleuronectes platessa; Estuary; Toxicity

The Mersey estuary is the most contaminated estuary in British waters (Collings, Johnson, & Leah, 1996; Fox, Johnson, Jones, Leah, & Copplestone, 1999). Detailed studies are underway on the pathology of flounder (Platichthys flesus) from the Mersey and on flounder from the nearby, but less contaminated, Dee estuary.

* Corresponding author. Tel.: +44-151-794-5120; fax: +44-1477-535-387. E-mail address: [email protected] (M.G. Simpson). 0141-1136/02/$ - see front matter # 2002 Elsevier Science Ltd. All rights reserved. PII: S0141-1136(02)00203-9

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Flounder breed offshore but spend a lot of time in the estuaries, penetrating into freshwater. These flatfish are in close contact with sediments. In contrast plaice (Pleuronectes platessa) are flatfish which enter the Mersey with the tidal flow but spend less time in the estuary than flounder and are therefore less likely to show evidence of pollutant exposure. In a previous histopathological study on the liver, kidney and gonad of flounder (P. flesus), Simpson, Parry, Kleinkauf, Swarbreck, and Leah, (2000) found pathological changes which were consistent with xenobiotic exposure. Comparative published data on plaice (P. platessa) was not found. There is probably much histopathological information in a variety of flatfish from European waters by UK government sources (e.g. CEFAS) and international agencies, such as ICES etc., but this information has not been published in peer reviewed journals and so is not available for citation and independent review, with some notable exceptions (Veetak & Wester, 1996; Allen, Matthiesson, Scott, Hawworth, & Thain, 1999). We are comparing the histopathology of major organs and tissues of flounder, plaice and sole (Solea solea) which can be found in this estuary with detailed histopathology of offshore populations of the same species. We report here on the histopathology of liver, kidney and gonad of plaice, a species of flatfish which enters the estuary with the tidal flow, spends time feeding but unlike the flounder does not remain long in the Mersey and its tributaries. The microscopic findings obtained for liver, kidney and gonad are reported here. Whilst trawling for flounder, other species were netted, including plaice, sole and whiting (Merlanea mergangea) plus a considerable number of gobies (> 200). Plaice (n=20) with a mean body weight 13.23  1.53 g, mean length 23.49  2.4 cm were netted in Autumn 1998. The fish were killed by a sharp ruler, the spinal cord severed and major organs and tissues removed at necropsy. Tissues were fixed in 10% buffered formalin, processed through ascending grades of alcohol, cleared in xylene and embedded in paraffin wax at 58–60  C. Transverse sections (TS) were cut at 5 mm and stained routinely with haematoxylin and eosin (H&E). Sections werexamined with a Polyvar photomicroscope under transmitted light and by Nomarski interference microscopy. Photographs were taken using Kodak EP64T film, transparencies scanned with CanoScan 2700F film scanner and edited, where appropriately, with Adobe photoshop. Histopathological abnormalities were not seen in the liver, kidney and gonads. The livers mostly were full of storage product, which from their shape the vacuoles appeared to be mostly lipid (Fig. 1) but Oil red O staining was not done to confirm this. In the gonads (Fig. 2) the testes were mostly full of ripe sperm and the ovaries were mostly at the vitellogenic stage. Helminth parasites were present in the body cavity in several fish, adjacent to the liver but had not induced any inflammatory and fibrotic changes in the serosa or parenchyma. In this study, a sample of 20 plaice showed no hepatic, renal and gonadal anomalies. Moreover, no papers were found in the peer reviewed literature on plaice histopathology except observations on Pleuronectes obsura (Syrasina, Arbuzoua, Zhadko, & Sokolousky, 2000) who found mainly gill changes. In industrial toxicological pathology, data has been collected on laboratory species, mostly rodent

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and dog, the incidental pathology is well understood and documented along with the histopathological effects of a vast array of chemicals. No such database is available for teleosts. Virtually no pathological changes were seen in the plaice, incidental or contaminant linked, which is probably a reflection of the small sample size available for study. However, it cannot be discounted that since the stay in the estuary is brief compared to flounder, pollutant exposure and duration of exposure is lessened. Also, plaice may have a different detoxification profile to flounder. To make real progress in fish toxicological pathology, it will be necessary to utilise the experimental pathology approach, so as to be able to better understand pathological changes that are being reported from field studies in Europe. Using an experimental approach sound data can be accumulated for basic histopathological changes (e.g., Okihiro & Hinton, 2000). Eventually, data will be accumulated on what is consistent with chemical exposure and what is incidental. Experimental pathology has contributed to much of our understanding of carcinogenesis in teleosts. Further progress requires detailed examination for non-neoplastic pathology.

Fig. 1. The accumulation of storage products in the liver which in marine flatfish is mostly neutral lipid, characterised by clear round vacuoles in wax sections (a). Glycogen is also a storage product and in wax sections appears as irregular vacuoles sometimes criss-crossed by strands of eosinophilic cytoplasm. (b) H & E stain.

Fig. 2. Gonadal staging in the plaice. (a) A male showing ripe sperm in the gonad. Interference contrast microscopy. H & E stain. (b) A female showing the early stages of vitellogenesis. H & E stain.

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References Allen, Y., Matthiessen, P., Scott, A. P., Hawworth, S., & Thain, J. E. (1999). Science of the Total Environment, 233, 5–20. Collings, S. E., Johnson, M. S., & Leah, R. T. (1996). Marine Environmental Research, 41, 281–297. Fox, W. M., Johnson, M. S., Jones, S., Leah, R. T., & Copplestone, D. (1999). Marine Environmental Research, 47, 311–329. Okihiro, M. S., & Hinton, D. (2000). Toxicologic Pathology, 28, 342–356. Simpson, M. G., Parry, M., Kleinkauf, A., Swarbreck, D., & Leah, R. T. (2000). Marine Environmental Research, 50, 283–287. Syasina, G., Arbuzova, L. L., Zhadko, E. A., & Sokolovsky, A. S. (2000). Biologiya Morya Vladivostk, 26, 265–271. Veetak, A. D., & Wester, P. W. (1996). Diseases Aquatic Organisms, 36, 99–116.