Toby Champneys – winner of the university’s inaugural Best Dissertation on Aquaculture and Fisheries.
The Effect of Stocking Density on Neophobia in Nile Tilapia (Oreochromis niloticus)
Stocking density is an important variable in aquaculture, as it affects growth, survival, welfare and ultimately production. Neophobia (a fear of the ‘new’) is an important behavioural adaptation in many taxa, including fish. Neophobia is adaptive in many scenarios and is thought to enhance survival, however, to what extent it is affected by density under aquaculture conditions is unknown. Nile tilapia is one of the world’s most cultured species, with a reputation for tolerating high stocking densities which has significant implications for welfare. Nile tilapia fingerlings were reared for six weeks at either high (50g/L) or low density (14g/L), exposed to a novel object and their behavioural response was recorded through various metrics. Fish reared at a high stocking density showed significantly higher levels of neophobia (higher aversion to the novel object) than those from low density and this trend was exacerbated when no cover was available. Fish reared at high density were also shyer, less aggressive, less mobile and showed a lower propensity to take risks by leaving cover than fish reared at low density. Thus the reactive coping style to novelty shown by high density fish was very different from the proactive coping style shown by fish reared at low density. These findings provide valuable insights into the effect of stocking density on Nile tilapia, and highlight the importance of considering behaviour when assessing the welfare of farmed fish.
Alice Wren – runner-up in the university’s inaugural Best Dissertation on Aquaculture and Fisheries.
The Influence of Human Activity on the Occurrence of Microplastics in European Plaice (Pleuronectes platessa) and Common Sole (Solea solea) in the Coastal Waters of Southwest Wales
The ubiquitous prevalence of microplastics in the marine environment is of growing environmental concern. The impacts of ingesting microplastics are well documented in marine organisms; ranging from false satiation and reduced distal intestine function to increased absorption of marine contaminates. All of which are detrimental to the health of exposed populations. Ingestion of microplastics has been confirmed in numerous marine organisms, however, data on the abundance in natural teleost populations is limited.
This study reports the occurrence of microplastics in the gastrointestinal tract of juvenile European plaice, Pleuronectes platessa and common sole, Solea solea in the coastal waters of Southwest Wales. Using the technique of dissolving the gastrointestinal tract in 15% KOH overnight to dissolve all organic material and isolate any microplastics present.
In total 186 fish were examined, of these, 32.3% of individuals had one or more microplastics present within the gut. Plastic particles observed were primarily fibres (47.4%) followed by beads (44.3%), fragments (5.2%) and films (3.1%). The proportion of individuals with microplastics present was significantly higher in Swansea Bay; an area of high human activity, compared to at Oxwich Bay; an area of low human activity. Suggesting that human activity influences the abundance of microplastics in coastal areas. It is likely that microbeads and fibres from washing clothes are a major contributor of microplastics in Swansea Bay due to the present of sewage outfall pipes.
Future research should focus on the long-term effects of microplastic ingestion in fish in order to further assess the extent to which microplastics are impacting marine organisms.