What researchers used an experimental paradigm, they called

What is enrichment?

Environmental enrichment is
closely related to behavioural enrichment. It is an animal husbandry principle
that aims to enhance the quality of life of captive animals. It provides and
identifies stimuli for necessary psychological and physiological well-being. (Shepherdson, Mellen, Hutchins, 1998).
Environmental enrichment aims to improve or maintain an animal’s health by
increasing the number of species- specific behaviour, and also increasing
positive utilisation of the captive environment. Its aim is to prevent or reduce
abnormal behaviour, as well as enhancing an animal’s ability to cope with

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A paper that shows this is Environmental Enrichment Reduces A? Levels
and Amyloid Deposition in Transgenic Mice. The researchers used an
experimental paradigm, they called environmental enrichment. Lazarou et al first exposed male
transgenic mice to an enriched environment. Secondly, they experimented with
steady levels of soluble and formic acid – soluble A? peptides. They were
reduced in enriched mice compared to standard housing mice. Western blot
analyses showed enrichment does not alter APP processing but alters levels of
accumulated A? peptides. Several critical approaches were noted in the
experimental approaches when compared to Jankowsky
et al (2003). Thirdly, they showed the activity of A? – degrading protease
and neprilysin is elevated in enriched mice. Lastly they employed high –
density oligonucleotide arrays which showed elevation in the endothelial cell
activated in enriched mice. (Lazarov et
al., 2005)

Robert Young believed people involved in environmental
enrichment should have a basic understanding of animal welfare. Robert Young mentioned two definitions
of environmental enrichment. Environmental enrichment describes how
environments of animals in captivity can change for the benefit of the animals.
Young used this definition from Shepherdson, 1994. However Young also used this definition from BHAG, 1999 provided by Valerie Hare. The definition states
environmental enrichment is a process for improving zoo environments and care
for the animals. It is a dynamic process with changes to structure and
husbandry practices with the aim to increase behavioural choices and drawing
out species behaviours and abilities. (Young,

Mason et al stated stereotypic behaviours in some captive wild
animals are well known in zoos and similar institutions. Wild captive species
need to be taken seriously and in terms of enrichment which can lead to central
nervous system dysfunction. Stereotypic behaviours may be expressed in animals
to cope with sub-optimal environments. They are only expressed when natural
activities are not available. Mason et al
argued that the best welfare option is to provide appropriate enrichments
that animals can choose to interact with. Abnormal repetitive behaviour may
indicate a risk to cross-species, suggesting enrichment changes to the root of
the problem. Habitats that induce abnormal repetitive behaviour can be poorer
than those which do not. Animals within sub-optimal environments can fare
better than non-stereotypic animals. Mason
et al emphasised reliable and valid welfare assessments require more than just
data on abnormal repetitive behaviour. Potential measures of stress and
welfare, also assessing how much animal’s value enrichment, can also be used. (Mason et al., 2007) 

A variety of environmental
enrichments is used to create outcomes that match an animals individual and
species history. The techniques used aim to stimulate the animal’s senses to
mimic their usage in the wild. Enrichment can be seen as auditory, olfactory, habitational
factors and food. (Smithsonian’s National
Zoo). Environmental enrichment can be offered to captive animals in a range
of locations including zoos and sanctuaries. It can be beneficial to a wide
range of animals e.g. land mammals, marine mammals and amphibians. (Ammpa.org).

The Association of Zoos and
Aquariums (AZA) requires that husbandry and welfare is a main concern for animals
in captivity. AZA promotes the overall wellbeing of animals encompassing the mental,
physical, social and biological characteristics. (Aza, 2013). 



An animal’s interest that is
evoked by any stimulus is considered enriching, this includes both natural and
artificial objects, scents and novel foods. (Smithsonian’s
National Zoo). Most enrichment stimuli can
be divided into seven groups:

Changes which add complexity to the captive animal’s environment.

Feeding: To present food to an animal in different ways.
E.g. hidden, scattered, buried, presented differently and food that is

Manipulation: Items that can be manipulated by paws, feet, tail,
head, mouth etc. The aim is to promote investigatory behaviour and exploratory
play that is closely related to behaviours that are seen in the wild.

Pig producers are required to
provide enrichment for pigs to enable proper investigation and manipulation
activities. Scott et al showed single
or multiple hanging toys were able to show a comparable level of occupation to
that of the straw bedding. Toy manipulation only represented 5% of the
remaining time. Manipulation of a single toy did not differ between the housing
systems. Scott et al results
suggested behaviour was more focused on enrichment toys. The type of feeding
may influence levels of enrichment manipulation. A pig playing with enrichment
may cause that object to become more interesting to the other pigs. Levels of
toy manipulation were low in the study, possibly to the extent that there was
no social competition. This suggested that one toy would cater for all pigs.
The lack of skin lesions scores indicated a lack of aggressive behaviour. (Scott et al., 2007)

Puzzles: Given to animals as simple problems that contain

Sensory: Animal senses are stimulated e.g. visual,
olfactory, auditory, tactile, and taste. (Smithsonian’s
National Zoo)

Assessment of Environmental Enrichment

A wide range of methods can be
used to assess the most appropriate environment enrichments to be used. These
are used on the premise that captive animals should perform behaviours that are
similar to their ancestral species. (Dawkins, 1989). One method is preference test studies, which leaves the
animal free to choose which activity or interaction they most prefer. (Sherwin and Glen, 2003). Another method
is motivation studies, which assesses the impact of environmental enrichment on
an animal’s motivation. (Sherwin and
Glen, 2003). The assessment can include some or all the general approaches
listed above.   

mice were offered a choice between white, black, green and red cages. Most of
the mice preferred white cages, then black or green, red was the least
preferred cage. Familiar environment can influence preference choice. Sherwin and Glen showed 17 of the 24
mice chose cages different to their home cage showing familiarity has little
preference. Not much is known about how mice visually perceive their
environment. It remains uncertain what influences cage preferences in mice.
Food consumption and body weight were inversely related. E.g. the heaviest
mouse ate less food. Sherwin and Glen speculated
cage colour effect on these characteristics could relate to home cage activity.
Mice from the white home cages had the highest food consumption and the lowest
body weight. Home cage colour influenced mice behaviour in the raised plus
maze. Mice in red cages spent more time in the closed arms than white home cage
colour. The maze is established to test behaviour and used to indicate fear or
anxiety. Greater use of closed arms in the maze indicates a more anxious or
fearful animal. Characteristics of home cage rodents influenced the responses
of laboratory rodents in behavioural tests of emotionality. Red cages were
least preferred and the mice showed the greatest amount of anxiety. White cages
may have lowered or did not change the level of anxiety, whereas red cages may
have increased the levels of anxiety. (Sherwin
and Glen, 2003).


based enrichment can be
as simple as leaving
food whole or for those animals able to climb throwing it on the roof of
the enclosure or a raised platform. It can also be
scattered, hidden or concealed in paper sacks.

most common sensory enrichment is olfactory. Using items such as herbs, spices,
perfume, deodorant, catnip and toothpaste.

enrichment uses objects such as Boomer Balls, Kong toys, tyres, cardboard tubes
and fireman’s hoses to occupy the animals time.

can be used as a form of social enrichment to effect mating and natural behaviours.

to the physical habitat include hiding food, adding enrichment objects to
encourage natural behaviour and enhance their space to provide mental
stimulation. (Colchester Zoo).


Enrichment Articles


of Collard Green Stalks as Environmental Enrichment for Cockatiels Kept in
Captivity. They found the stalks increased food intake and reduced
sleep activities. There was no effect on body surface temperature, locomotion,
maintenance and other resting activities. Green stalks proved they can be used
as enrichment, but did not significantly alter their overall behaviour. Lower
sleeping activities were observed in the group with the green stalks (the
enriched group). The result indicated that enrichment could be a promising
strategy to reduce the fear response in captive parrots and similar birds. (Carvalho et al, 2017).

of Environmental Enrichment on the Behaviour Performance and Meat Quality of
Domestic Pigs. They found that pigs with an enriched environment showed
more exploratory behaviour spending more than a quarter of their time
exhibiting that characteristic. In a barren environment pigs showed more time
exploring the fixtures of the pen than the other pigs. They also were involved
in more harmful behaviour e.g. nosing other pigs, biting other pigs and
aggressive head thrusting. Environmental enrichment improves the welfare of
pigs by reducing anti-social behaviour and an additional benefit of improving
meat quality. (Beattie, O’Connell and
Moss, 2000).

These two papers confirm that environmental
enrichment is beneficial but there are other papers that have also researched
enrichment in animals and have stated otherwise. In the case of the Cockatiels
the objective of the enrichment was to improve the behaviour and reduce the
fear response which leads to undesirable behaviour. This statement also relates
to Sherwin and Glen, 2003, they
looked into the fear and anxiety of mice in coloured cages and in the raised
plus maze.  However the study of the pigs
differed in that there was a commercial driver to the enrichment and whilst
they also exhibited better behaviour the commercial spin off was better meat


about Laboratory Fish


Laboratory fish are very useful for a variety
of experiments.

Immunoassays for Predicting the Toxicity of Malathion in a Laboratory Fish
Model. The
use of non-rodent species has increased for immunotoxicological evaluation of
chemicals. Fish are phylogenetically distant from humans. Fish contain a number
of structural, functional and biochemical characteristics. Fish offer
advantages over the immunotoxicological mammalian models. Beaman et al, investigated the utility of NTP – validated mammalian
immune assays. The results will help to explain a specific panel of immune
assays. The significant finding was sub chronic exposure of medaka to sub
lethal concentrations of Malathion which had little effect on immune functions.
Malathion showed to produce neurotoxicity in fish similar in mammals. PFC
(Plaque-forming Cell) response requires a concentrated effort which is
difficult in medaka and requires further study. Beaman et al, results demonstrated sub chronic exposure to
non-lethal concentrations of Malathion increased host susceptibility. When PFC
was suppressed host resistance was compromised.  Beaman
et al, also showed mammalian immune assays can be used successfully in fish
to show toxicological hazards. (Beaman et
al., 1999)

Fertile and
diploid nuclear transplants derived from embryonic cells of a small laboratory
fish, medaka. Wakamatsu et al transplanted embryonic cell nuclei in to unfertilized
eggs of medaka. Six transplants grew into adults, they were fertile and
homozygous and introduced marker genes. Genetic markers were passed down the
generations in a Mendelian fashion. Wakamatsu
et al demonstrated successful nuclear transplantation in fish. The first experiment
was the GFP gene was driven by a promoter gene (medaka EF-1a-A). The results
indicated the transgene from the donor was expressed with characteristics of
the promoter. The second experiment consisted of the GFP transgene expressed in
the same pattern as the donor transgenic fish. Wakamatsu et al demonstrated nuclei of medaka blastula cells are
totipotent. The survival rate of nuclear transplants after the blastula stage
was lower in the first experiment when compared to the second one. In the first
experiment PGM allozyme markers in the eggs was not detected. The genetic
markers of the recipient fish were not obtained in the first or second
experiment. (Wakamatsu et al., 2001)


about Enrichment in Fish


Change Enhances Cognitive Abilities in Fish. They found
variations in food rations for Cichlid fish (Simochromis pleurosphilus) in early life outperformed fish that had
constant rations. This suggested environmental enrichment changes in early life
trigger a better cognitive performance. The fish were tested one year later and
the difference in their cognitive ability stayed the same. Kotrschal and Taborsky suggested a single change can improve
cognitive abilities for maybe a lifetime. Food rations were different for
juveniles as they were a range of sizes. Fish given less food showed more
motivation to eat the food. When in adult hood, the fish sizes were all the
same, so motivation had been lost. (Kotrschal
and Taborsky, 2010)  

Enrichment Promotes Neural Plasticity and Cognitive Ability in Fish. They found that
juvenile salmon that experienced an enriched environment for 8 weeks had
increased ability to compensate for injury and adjust their activities in
response to new situations (neural plasticity). The enriched fish were given a
maze and made fewer mistakes. Salvanes et
al concluded that salmon exposed to an enriched environment during a
rearing period had a positive effect on cognitive learning. The salmon raised
in the non-enriched environment exhibited a disadvantage in cognitive learning.
Enrichment, with regard to salmon has been found to have a positive on neural
plasticity and spatial learning. (Salvanes
et al, 2013).

Both agree enrichment can have a positive effect
on fish. Environmental enrichment can help fish in a manner of learning. The
two articles illustrate that when fish are placed in an enriched environment
early in their life the result is positive changes in their behaviour and
cognitive ability.

behaviour in laboratory zebrafish: potential benefits of exploring the unknown.
Quality of
life led by animals is influenced by cognitive stimulation. Exploration
opportunities in captive enrichment programs proved beneficial for improving welfare.
Cognitive enrichment cannot exceed the skills and resources of the animal in
order for it to be effective. In Graham’s
study zebrafish were quick to swim into the newly released area and this
interest continued over the days observed. Fish did not express anxious
behaviour, but did engage in affiliative behaviour. The evidence suggested
exploration behaviour may induce a positive emotional state. Zebrafish are
known to show anxiety, a measure of this is spatial location in the tank. Graham first studied zebrafish behaviour
in tanks. The fish were provided access to an unexplored area. The findings of
this study show the fish did not show any anxiety. The fish stayed closer
together when more space was added to the tank. Graham’s finding of increased cohesion and co-ordination in the
absence of threat showed distress may not be an only driver of the group.
Normally laboratory housing for zebrafish consist of small or barren tanks.
Animals in the wild have the opportunity to explore their environment freely.
Laboratory environments have resulted in abnormalities in behaviour. The
findings from this study suggests social behaviour of zebrafish is affected by
positive situations. Graham’s findings
suggested a more natural environment is important for animal welfare and so is
the opportunity to explore.  (Graham, 2017)


behaviour in all species articles


Do all
animals sleep? One assumption made is all animals or those with a nervous system sleep.
Another assumption is sleep deprivation is very harmful. The assumptions
combined suggest sleep is a vital function. Most animals adjust their activity
to the conditions they inhabit. Reduced alertness and activity in animals
cannot be associated with sleep. Sleep in animals is when circadian rhythms
have been eliminated. It is important to not mix sleep with rest. Sleep can be
defined as a reversible state of immobility and reduced sensory responsiveness.
Two types of sleep have been found in mammals, non-REM sleep and REM sleep. Non-REM
sleep is reduced activity in brainstem systems, whereas REM sleep is a pattern
of discharge that resembles a ‘waking’ in most brain regions.  To Siegel’s
knowledge there hasn’t yet been any claim of sleep in unicellular organisms.
Rest deprivations in cockroaches did not produce a consistent increase in rest
time during a recovery period. Drosophila
have been found to show a behavioural state which meets the criteria of
sleep. In studies of sleep behaviour in zebrafish, circadian variations in
activity and responsiveness increased and a decrease in response to stimuli was
seen after rest deprivation. Activation of the perch by light during their
inactive periods resulted in an increase of rest behaviour during the subsequent
12 hour period. In a study of activity and responsiveness in the bullfrog this showed
levels of activity varied in a circadian pattern. The bullfrog was more alert
during periods of inactivity when compared to periods of activity. In a study
of the tree frog it was concluded this species slept. In the turtle, quiescent
behaviour increased after disruption of quiescent states. Birds have been found
to show REM and non-REM sleep. Sleep has been studied in a few mammalian
domesticated species, these species met the general definition of sleep. Using
only behavioural responses Siegel cannot
safely say herbivores meet the criteria for sleep. Sleep in the fur seal on
land can resemble terrestrial mammals. In dolphins and cetaceans is quite
different, they only show uni-hemispheric slow waves. In smaller cetaceans,
motor activity in continuous from birth to death. (Siegel, 2008)

to the function of mammalian sleep. Sleep can be defined as a state of immobility
with reduced responsiveness. The changes in brain metabolism and neuronal
activity during sleep increases when compared to most waking periods. In this
article Siegel considered the
knowledge that has been gained about sleep and sleep – control mechanisms.
Neurophysiological studies have provided a lot information about the mechanisms
controlling sleep. Non-REM sleep can be started by the isolated forebrain. REM
sleep can be started by the isolated brainstem. Changes in localised
temperature in the brainstem and forebrain cannot be confused with
environmental temperature. Recent studies suggest that the cessation of
histamine neuron activity can be linked to the loss of consciousness in sleep.
To study theories of REM and non-REM sleep function, you have to consider how
sleep amounts differ across species. A species diet can be correlated with
sleep time. Another aspect of sleep is linked to body mass and brain size.
Studies on mammalian sleep have been mainly researched on placental or
marsupial mammals. Terrestrial mammals show relatively high – voltage
neocortical EEG activity during non-REM sleep. Slow wave and spindle waves are
not enough as evidence of sleep. Studies of arousal has not been performed on cetaceans
across putative sleep – wake cycles. Terrestrial mammals have minimal activity
and maximum sleep. Siegel hypothesised
that the continuous activity of cetaceans has adaptive value. Fur seals exhibit
differences in sleep when compared to terrestrial mammals. There are lots of
theories to explain the functions of REM and non-REM sleep. A common theme in
theories is sleep time, it is determined by neuronal activity in the neocortex.
Neocortical size does not seem to be a determinant of non-REM or REM sleep
amounts. Sleep restriction leads to feelings of sleepiness. Skin lesions,
hyperthermia followed by hypothermia, increased food intake and death are signs
of long – term sleep deprivation. Sleep may be adaptive as it conserves and
suppresses energy across a 24 hour day. Energy conservation can be important in
newborns. Sleep may be able to defend against stress in herbivores. Sleep can
have multiple functions for the brain and body. (Siegel, 2005)


behaviour in fish articles


Zebrafish as a Model Organism for Behavioural Genetics. Sleep behaviour
and physiological function is not fully understood but is a widespread
phenomenon. At night zebrafish have periods of two to four minutes of
inactivity, floating horizontally whilst making small pectoral fin movements.
Zebrafish have also been found to have a reduction of facial movements which
suggests lower respiratory levels. Any disruption e.g. light, vibration,
electric shock or forced movement, in sleep behaviour increases sleep
deprivation. Zebrafish also show daily rhythmic cycles that can be influenced
by the environment (circadian rhythmicity). (Norton
and Bally-Cuif, 2010)

of Sleep in Zebrafish and Insomnia in Hypocretin Receptor Mutants. The research
centered on the increased arousal threshold for zebrafish and the degree to
which this was reversible by gentle tapping, acoustic stimulation or weak
electrical field. Fish in the active state were more likely to respond to lower
voltage stimuli however at higher voltages all fish responded irrespective of
their state. With regard to tapping or acoustic stimuli rapid habituation was
noticed and therefore in an effort to create sleep deprivation the electrical
stimuli was retained as habituation was less of a problem. The end result was
that sleep deprivation was achieved, and on releasing into a dark environment
this resulted in modest sleep recovery in those that were partially deprived
and significant recovery in those that were fully sleep deprived. However when
the sleep deprived fish were released into light there was no sleep rebound. (Yokogawa et al., 2007) 


it all links together

Environmental enrichment is beneficial for wild
and domestic species. A variety of enrichment techniques can be used to
generate a number of beneficial outcomes. There is a range of drivers that
require the use of enrichment, whether they are commercial for domestic
livestock or helping different species cope with captivity. With particular
regard to fish, the range of enrichment alternatives is narrower than that
available for mammals and birds. Enrichment with regard to fish is largely
restricted to availability of food as highlighted in Kotrschal and Taborsky and Salvanes, et al. Further research
conducted by Yokogawa, et al explored
in detail the effect on sleep deprivation on zebrafish with particular
reference to the types and strengths of stimuli to arouse the fish from the
sleep-like state. The research was further expanded to examine the homeostatic
response when sleep deprived fish were released into either a light or dark
environment. In this study fish,
sleep and enrichment will be combined together.  




The aim for this project is to
see if enrichment given to fish during the day effects the sleep behaviour of
fish during the night.