Swimming exercise enhances brain plasticity in fish

It is well-established that sustained exercise training can enhance brain plasticity and boost cognitive performance in mammals, but this phenomenon has not received much attention in fish. The aim of this study was to determine whether sustained swimming exercise can enhance brain plasticity in juvenile Atlantic salmon. Brain plasticity was assessed by both mapping the whole telencephalon transcriptome and conducting telencephalic region-specific microdissections on target genes. We found that 1772 transcripts were differentially expressed between the exercise and control groups. Gene ontology (GO) analysis identified 195 and 272 GO categories with a significant overrepresentation of up- or downregulated transcripts, respectively. A multitude of these GO categories was associated with neuronal excitability, neuronal signalling, cell proliferation and neurite outgrowth (i.e. cognition-related neuronal markers). Additionally, we found an increase in proliferating cell nuclear antigen (pcna) after both three and eight weeks of exercise in the equivalent to the hippocampus in fish. Furthermore, the expression of the neural plasticity markers synaptotagmin (syt) and brain-derived neurotrophic factor (bdnf) were also increased due to exercise in the equivalent to the lateral septum in fish. In conclusion, this is the first time that swimming exercise has been directly linked to increased telencephalic neurogenesis and neural plasticity in a teleost, and our results pave the way for future studies on exercise-induced neuroplasticity in fish.</p

Aerobic swimming in intensive finfish aquaculture: applications for production, mitigation and selection

We review knowledge on applications of sustained aerobic swimming as a tool to promote productivity and welfare of farmed fish species. There has been extensive interest in whether providing active species with a current to swim against can promote growth. The results are not conclusive but the studies have varied in species, life stage, swimming speed applied, feeding regime, stocking density and other factors. Therefore, much remains to be understood about mechanisms underlying findings of ‘swimming‐enhanced growth’, in particular to demonstrate that swimming can improve feed conversion ratio and dietary protein retention under true aquaculture conditions. There has also been research into whether swimming can alleviate chronic stress, once again on a range of species and life stages. The evidence is mixed but swimming does improve recovery from acute stresses such as handling or confinement. Research into issues such as whether swimming can improve immune function and promote cognitive function is still at an early stage and should be encouraged. There is promising evidence that swimming can inhibit precocious sexual maturation in some species, so studies should be broadened to other species where precocious maturation is a problem. Swimming performance is a heritable trait and may prove a useful selection tool, especially if it is related to overall robustness. More research is required to better understand the advantages that swimming may provide to the fish farmer, in terms of production, mitigation and selection

Effects of the hatchery environment on neurobiology and behaviour in Atlantic salmon : implications for stocking

The Atlantic salmon (Salmo salar) is an iconic fish species with a widespread historic abundance, but recent decades have witnessed a dramatic decline in wild stocks due to a variety of anthropogenic factors, especially overfishing and loss of habitat. To mitigate the impacts of these anthropogenic effects, millions of hatchery-reared Atlantic salmon are released yearly into rivers through stocking programs, which aim to augment the productivity of wild populations. However, these stocked fish are reared under uniform and stimulus-poor hatchery conditions and consequently, they are behaviourally naïve at time of release. For example, hatchery-reared salmonids often show impaired foraging and antipredator behaviour compared to wild conspecifics, which contributes to the observed high post-release mortality rates in stocked fish. Although the effects of the hatchery environment on fish behaviour are relatively well described, the brain, which is the key organ that translates environmental stimuli into appropriate behavioural responses, remains gravely understudied. The few studies which have investigated the impact of the hatchery environment on the fish central nervous system have mostly mapped the expression of neuroplasticity and neurogenesis genes in the entire brain, or large brain structures, such as the whole telencephalon. However, the brain is a complex organ, composed of a plethora of neural subpopulations, each with distinct functionalities and characteristics. When quantifying whole-brain levels of neuroplasticity markers, one studies a conglomerate of many different neural subregions, and regional differences can therefore not be detected. The aim of this thesis is to gain a better insight into the neural differences between wild and hatchery-reared fish, specifically within neural subpopulations of the telencephalon, and how innovative hatchery protocols can improve the neurobiology, behaviour and post-release survival of hatchery-reared salmon. First, we made a detailed characterisation of the neurobiology of juvenile wild and hatchery-reared Atlantic salmon parr. This was achieved by quantifying the expression of the neuroplasticity marker brain-derived neurotrophic factor (bdnf) and the neural activity marker cfos in five neural populations within the telencephalon of wild and hatchery-reared juvenile salmon under both basal and acute-stress conditions (Paper I). We found that expression of bdnf and cfos varied greatly between the studied telencephalic subregions, confirming that these subregions have a distinct responsiveness to environmental stimuli. Compared to wild fish, hatchery-reared fish of the same genetic origin showed higher post-stress neural activation in the ventral area of the dorsolateral pallium (Dlv), which is an important brain region associated with relational memory and spatial orientation. Furthermore, wild fish displayed stress-induced upregulation of bdnf in the dorsomedial pallium (Dm), which regulates emotional learning and stress reactivity, while this was not the case for hatchery-reared individuals. This study showed that targeting telencephalic subregions can reveal expression patterns that escape detection when studying the entire telencephalon as a whole. Moreover, we demonstrated that the hatchery environment affects neuroplasticity and neural activation in brain regions which are important for learning processes and stress reactivity, providing a neuronal foundation for the behavioural differences observed between wild and hatchery-reared fish. After we had characterised neural differences in telencephalic subregions between wild and hatchery-reared salmon, we assessed whether structural environmental enrichment (EE) of the rearing environment could increase region-specific neural plasticity and stocking success in hatchery-reared salmon (Paper II). After seven weeks of treatment, EE-reared parr showed higher post-release freshwater survival rates compared to control individuals, which were reared in standard uniform hatchery tanks. This improved stocking performance did not, however, appear to be linked to significant changes in the expression of telencephalic plasticity markers. Although structural EE has shown some, albeit inconsistent, beneficial effects on fish stocking success across studies, hatchery managers are reluctant to implement this measure in their hatcheries because of hygienic and operational limitations. Therefore, it is important to develop alternative rearing methods which can enhance fish neural development and are more practical to implement in the hatchery. One of these alternative rearing methods is swimming exercise, which has previously been linked to increased post-release survival in salmonids. As running exercise is associated with increased neural plasticity in mammals, we investigated in Paper III whether swimming exercise could serve as an alternative rearing strategy to promote Atlantic salmon neural plasticity and cognition. After eight weeks of sustained swimming, we found increased expression of neuroplasticity-related transcripts in the telencephalon transcriptome of exercised salmon. However, we did not find any evidence for increased cognition in exercised fish, in terms of their ability to solve a spatial orientation task in a maze test. While previous studies have reported positive physiological effects of swimming exercise, such as improved growth efficiency and stress reduction, this is the first time that exercise-enhanced neural plasticity has been reported in salmonids, building a case for exploring further the potential of implementing swimming exercise to improve the stocking success of reared salmonids. In summary, the results presented in this thesis advance the field of applied fish neurobiology in a stocking context by characterising telencephalic neural plasticity markers in Atlantic salmon on a more detailed level than previously studied. We demonstrate that EE can improve juvenile salmon survival during freshwater residency, but that the effects of EE on neural plasticity are limited in the studied telencephalic regions. We identify swimming exercise as a promising novel tool to improve neural plasticity in salmon, and we remark that exercise has additional physiological benefits and is relatively easy to implement in hatcheries. We therefore suggest that future work should aim at validating the potential use of exercise in the optimisation of hatchery conditions for stocking programs, and that further research is needed to increase our understanding on the link between the rearing environment, the brain and behaviour

Neurobiology of Wild and Hatchery-Reared Atlantic Salmon: How Nurture Drives Neuroplasticity

Contains fulltext : 195541.pdf (publisher's version ) (Open Access

Swimming exercise enhances brain plasticity in fish

It is well-established that sustained exercise training can enhance brain plasticity and boost cognitive performance in mammals, but this phenomenon has not received much attention in fish. The aim of this study was to determine whether sustained swimming exercise can enhance brain plasticity in juvenile Atlantic salmon. Brain plasticity was assessed by both mapping the whole telencephalon transcriptome and conducting telencephalic region-specific microdissections on target genes. We found that 1772 transcripts were differentially expressed between the exercise and control groups. Gene ontology (GO) analysis identified 195 and 272 GO categories with a significant overrepresentation of up- or downregulated transcripts, respectively. A multitude of these GO categories was associated with neuronal excitability, neuronal signalling, cell proliferation and neurite outgrowth (i.e. cognition-related neuronal markers). Additionally, we found an increase in proliferating cell nuclear antigen (pcna) after both three and eight weeks of exercise in the equivalent to the hippocampus in fish. Furthermore, the expression of the neural plasticity markers synaptotagmin (syt) and brain-derived neurotrophic factor (bdnf) were also increased due to exercise in the equivalent to the lateral septum in fish. In conclusion, this is the first time that swimming exercise has been directly linked to increased telencephalic neurogenesis and neural plasticity in a teleost, and our results pave the way for future studies on exercise-induced neuroplasticity in fish

Supplementary material from "Swimming exercise enhances brain plasticity in fish"

It is well-established that sustained exercise training can enhance brain plasticity and boost cognitive performance in mammals, but this phenomenon has not received much attention in fish. The aim of this study was to determine whether sustained swimming exercise can enhance brain plasticity in juvenile Atlantic salmon. Brain plasticity was assessed by both mapping the whole telencephalon transcriptome and conducting telencephalic region-specific microdissections on target genes. We found that 1772 transcripts were differentially expressed between the exercise and control groups. Gene ontology (GO) analysis identified 195 and 272 GO categories with a significant overrepresentation of up- or downregulated transcripts, respectively. A multitude of these GO categories was associated with neuronal excitability, neuronal signalling, cell proliferation and neurite outgrowth (i.e. cognition-related neuronal markers). Additionally, we found an increase in proliferating cell nuclear antigen (pcna) after both three and eight weeks of exercise in the equivalent to the hippocampus in fish. Furthermore, the expression of the neural plasticity markers synaptotagmin (syt) and brain-derived neurotrophic factor (bdnf) were also increased due to exercise in the equivalent to the lateral septum in fish. In conclusion, this is the first time that swimming exercise has been directly linked to increased telencephalic neurogenesis and neural plasticity in a teleost, and our results pave the way for future studies on exercise-induced neuroplasticity in fish

The potential roles of sponges in integrated mariculture

This mini-review evaluates the use of marine sponges in integrated culture systems, two decades after the idea was first proposed. It was predicted that the concept would provide a double benefit: sponges would grow faster under higher organic loadings, and filtration by sponges would improve water quality. It is promising that the growth of some commercially interesting sponges is indeed faster in organically enriched areas. The applicability of sponges as filters for undesired microorganisms has been confirmed in laboratory studies. However, upscaled farming studies need to be done to demonstrate the value of sponges for in situ bioremediation of sewage discharge or waste produced by fish cages. In addition, a new idea is presented – the use of sponges as an engine to convert dissolved organic matter (DOM) into particulate organic matter (POM) that can be consumed by deposit feeders through a chain of processes termed the sponge loop. A theoretical design of an integrated culture with seaweeds (Gracilaria sp.), sponges (Halisarca caerulea) and sea cucumbers (Apostichopus japonica) shows that 37% of the part of the primary production that is excreted by the seaweeds as DOM can be directly recovered in sponge biomass and a subsequent 12% in sea cucumber biomass after mediation (conversion of DOM to POM) by sponges. Hence, the total recovery of DOM into (sponge and sea cucumber) biomass within this IMTA is 49%.</p