Abstract
The water quality of some freshwater catchments feeding into the Great Barrier Reef has elevated concentrations of suspended sediments, nutrients and photosystem II-inhibiting herbicides and other pesticides. To investigate potential impacts of changes in water quality on barramundi (Lates calcarifer) physiology, fish were collected from sites with different land-use patterns in tropical north Queensland. The transcript levels for two genes that can be markers for exposure to endocrine-disrupting chemicals were measured initially. Since we found some differences in the expression levels of these genes, controlled laboratory exposures were undertaken to try to identify the causative agent. RNA Seq was also used to characterize the hepatic transcriptomes of fish captured from the Daintree River, which drains a National Park and has a very low pesticide load. These transcriptomes were compared to those from fish captured in the Tully River, which drains agricultural areas and has higher pesticide loads. The differences in transcript abundance indicated elevated cortisol in fish from the Tully, with transcripts involved in fatty acid metabolism, amino acid metabolism, and citrate cycling were more abundant in these fish; and transcripts involved in immune responses were less abundant. Fish from the Tully also had an increased abundance of transcripts associated with xenobiotic metabolism. Previous laboratory studies have noted similar patterns in fish and amphibians exposed to atrazine. If these transcriptomic patterns are manifested at the whole organism level, the differences in water quality between the two rivers may affect organism growth and fitness.