Effects of substrate on the behaviour and welfare of ornamental fishes

Most research into the welfare and behaviour of ornamental fish species has focused
on conditions within the ornamental trade itself, with welfare once fishes reach their
end destination of home aquaria often overlooked. Additionally, there is little
documented evidence on common husbandry practices carried out by hobbyists
across the UK, including the use of enrichment in aquaria. A variety of enrichment
types are available to the home aquarist including physical enrichment (e.g., plants,
substrate), dietary enrichment and sensory enrichment (e.g. lighting) but there has
been only a small amount of research into the effects of adding enrichment to home
aquaria. While some enrichment may be beneficial through increased environmental
complexity stimulating the expression of natural behaviours, the addition of some
types of physical structures, in particular substrate, can increase the growth of
potentially harmful bacteria. This thesis firstly reviewed current literature on fish
welfare, focusing particularly on the ornamental trade and the use of environmental
enrichment. The experimental component of the thesis comprised a lab study, which
used simulated home aquaria to record fish behaviour in relation to four different
substrate types. Simulated home aquaria containing a benthic (Corydoras sp.) and
open water (zebrafish; Danio rerio) fish species were maintained for 10 weeks during
which time behavioural recordings were carried out to understand the influence of
substrate on fish behaviour. To further understand hobbyist practices in the UK, a
survey of UK home aquarium owners was carried out to understand the most
popular fish species kept, the use of different enrichment types and how fishes are
cared for. In the experimental study, the type of substrate, including colour, was
found to affect fish behaviour particularly following the addition of food. More effects
were seen in the benthic Corydoras compared to zebrafish. The UK survey work
indicated that the majority of participants used substrate in their home aquaria,
although the most prominent reason given for use of substrate was aesthetic rather
than being welfare-orientated. In conclusion, the welfare of fishes within home
aquaria is still understudied, particularly when compared with research into the
welfare of other companion animals. Given the prevalence of substrate use in home
aquaria throughout the UK and its potential benefits for fish behaviour, there is a
need to further understand the negative aspects of this enrichment type through the
growth of harmful bacteria, which can cause disease and illness in both fishes and
humans.