Arguments Against Fish Enrichment

Evidence supporting the incorporation of enrichment materials into a captive mammal’s environment lead Pounder and his colleagues to investigate if doing so would be just as beneficial to captive fish. Fish are a hugely exploited research model as millions of tons of fish are farmed across the UK. Despite the massive commercial production occurring, inadequate research has been done on improving fish welfare in stressful situations. The large growth of the aquaculture industry should be synonymous with research about how to remedy production problems and facilitate humane treatment. In captivity, fish tanks are relatively under-stimulating compared to environments in the wild. It is thought that this disparity can cause stress or impaired cognitive function for the fish. It is simply recommended by the EU government that fish in captivity have enriched tanks. The fact that there has been little research done to discover potential benefits to enrichment might explain why there are no laws in place. Captive fish are often kept in barren tanks for reasons such as easy transfer and cleaning. Enriching a tank, in its most broad sense, refers to increasing the environmental complexity of the surroundings in a way that helps animal welfare. The results of research on environmental enrichment in fish may contradict each other, which indicates that species-specific considerations must be factored into the type of supplement used. Some positive effects regarding the effect of enrichment include increased brain development, reduced impact from stressors, improved foraging ability, improved post-release survival, and positive effects on growth. When fish are more adept at coping with various situations, an increase in neural plasticity occurs. However, it is possible for there to be negative or neutral associations with environmental enrichment. In order to find out what will benefit the captive fish the most, the best enrichment will have to consider the species and possibly even the life stage of the animal at the time of captivity. This study focuses on the species Onocorhynchus mykiss (rainbow trout) because of its wide usage as a commercially farmed fish and its lack of pre-existing information from research studies. This study aimed to investigate whether or not environmental enrichment would benefit the recovery of a rainbow trout from a stressor or invasive procedure and the degree of inter-individuality variability among the data found. Method: Juvenile rainbow trout were studied in stock tanks with two weeks to recover from the stress of transport. The tanks were equipped with light and dark cycles, aeration, and were kept at an appropriate temperature while being fed a standard fare trout diet. To begin the study, trout were transported at random and placed into an unenriched tank (n=32 trout) or a tank enriched (n=32 trout) with air, stone, gravel, a plastic plant, and an overhead area of cover. The feeding, light, aeration, and other environmental standards from the original tank were maintained in the study tanks. Fish were tested individually to account for social stresses caused by territorial behaviors within trout communities. Fish were randomly assigned to four treatment groups. Control fish were undisturbed, sham fish were anaesthetized in benzocaine water without invasive procedure, pain fish were given an acetic acid injections while under anesthesia, and stress fish were subject to air emersion for 1 minute. It is vital to know if enrichment can offset pain and stress by increasing recovery from experimentally induced stress that is commonly conducted in a laboratory. The painful stimuli only lasted 3 hours, and did not cause long term harm …show more content…
There failed to be a difference in OBR between any treatment group and environment. Recovery was expedited in regards to stress for fish in an enriched environment as opposed to fish in barren environments. Judging from this study, it is unclear whether the peak level of OBR or the recovery time is a more important indicator of the importance of enrichment. There was no enrichment effect on cortisol concentrations, but this factor may be influenced by the fact that the fish are checked after a 3 hour delay (peak acute stress is 1 hour post-stressor). Enrichment fish did experience lower coefficients of variation for cortisol levels than barren environment fish. Plasma cortisol was elevated for sham and pain group including a stress response. There are clear benefits for recovery for fish as long as enrichment is species