Seasonal variation in haematological parameters and oxidative stress bio-markers for selected fish species collected from the Flag Boshielo Dam, Olifants River System, Limpopo Province, South Africa

Abstract

Water is an essential and yet scarce resource, which has a vital role for human use and also serve as a habitat for numerous organisms in aquatic environments. Despite its scarcity there have been many reports indicating that it is continually polluted by domestic, agricultural, mining and other anthropogenic activities; subsequently affecting the health of organisms residing in such water bodies. Fish have been selected as the bio-monitoring species due to its direct interaction with the environment; thereby making it an appropriate model to monitor and evaluate the health status of the environment. The feral population of the alien species, Hypopthalmichtys molitrix (Valenciennes, 1844) commonly known as the silver carp in Flag Boshielo Dam has been considered a healthy population. However, this perception changed considerably after reports of lethargic, dying fish were first noted in 2011. Currently the sporadic deaths amongst mature specimens (>0.7m) persist; and the reason(s) for their demise remains unclear. Therefore, the aim was to employ a seasonal study design to investigate the health status of selected fish species such as H. molitrix in Flag Boshielo Dam by evaluating haematological parameters, oxidative stress biomarkers and bio-accumulation levels of particular transition metals. Seasonal surveys were carried out from February 2012 to January 2013 at Flag Boshielo Dam, Olifants River System, Limpopo Province. The locality surrounding the dam is known to be in an agriculture and mining catchment. Hypopthalmichtys molitrix and Labeo rosae (Steindachner, 1894) commonly known as the rednose labeo were collected with the use of scoop nets, conventional angling gear and gill nets. Following collection, morphometric measurements were taken and blood was collected. The blood samples required for further analysis at the Medical Science Department, University of Limpopo were kept on ice (4˚C). After the collection of all blood samples the specific fish was sacrificed and muscle samples were collected for bio-accumulation analysis and gills and liver samples were collected for the measurement of oxidative stress biomarkers. These tissue samples were rapidly frozen and kept frozen (-85˚C) until further analysis. Haematological parameters from the study reflected a variation amongst comparison of the inter- and intra-species. It was observed that mature H. molitrix suffered from anaemia. The response of glutathione-S-transferase (GST) and thiobarbituric acid reactive substances (TBARS) was relatively constant throughout all seasons when the young (<0.5m) and mature H. molitrix (0.6 – 0.90m) specimens were compared. However, the catalase (CAT) response of mature H. molitrix was dramatically impaired. This would increase their vulnerability to oxidative stress. Bioaccumulation levels of the eleven selected transition elements exhibited various trends. Metals such as Molybdenum (Mo), Vanadium (V), (Chromium) Cr, Cobalt (Co), Zinc (Zn), Cadmium (Cd) and Mercury (Hg) exhibited seasonal bio-accumulation levels that were in support of the various feeding behaviours of the fish species in this study. On the other hand, metals such as Manganese (Mn), Iron (Fe), Copper (Cu), Zinc (Zn), Cadmium (Cd) and Mercury (Hg) also illustrated the potential to be contributing factors in the death of the mature specimens. In conclusion, the findings from this study illustrate the complex nature of metabolic disturbances resulting in the death of mature H. molitrix specimens. It is clear that no single aspect investigated in this study could be solely implicated as the major cause of death. This multifactorial presentation necessitates further haematological assessment focussing on blood cell morphology and pathology, as well as investigations into other oxidative stress biomarkers in liver and gill tissue. In addition, identifying the most appropriate tissue type for future bio-accumulation measurements of transition metals in this feral population is necessitated. It is further suggested that neuro-muscular assessments, focussing on neurotransmitters such as γ-aminobutyric acid (GABA) and acetylcholine (Ach), form part of the investigation into the lethargic behaviour of the mature fish.