Aquaculture: Endocrine and Stress Effects on Fish Feeding

This report delves into the endocrine control of feeding in fish, examining the intricate interplay of neurohormones and environmental factors in aquaculture. It begins by exploring the physiological stress responses that can reduce food intake and disrupt the balance of orexigenic and anorexigenic components, impacting nutrient sensing within the hypothalamus. The report then investigates the evidence for natural behavioral rhythms in fish feeding, highlighting the influence of both endogenous biological clocks and environmental cues like light and temperature, and the endocrine mechanisms that regulate these rhythms. Finally, the report analyzes how the activation of the stress response in aquaculture, induced by factors such as crowding and poor water quality, can affect the neurohormonal control of food intake, including the roles of CRF, UI, and cortisol, and their impact on appetite regulation. The report synthesizes current research to provide a comprehensive overview of the complex factors governing fish feeding in aquaculture.

Running Head: AQUACULTURE
Aquaculture
Name
Institution

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Aquaculture
Question 1
Physiological Stress
Reduced food intake
Increase of the dopaminergic and serotonergic activity in the fish brain
HPI and HSC axis are activated
Leads to the increase of several components with known anorexigenic properties
Orexigenic components like neuropeptides NPY and AgRP are increased
Nutrient signals are not properly sensed by the hypothalamus

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Question 2
What is the evidence that fish display natural behavioural rhythms in food intake?
The control of the intake of food in fish is a very multifaceted and entails connection
amongst the systems that control the homeostatic and circadian cycle among central nervous
system (CNS), and the gastrointestinal tract besides the ambience. Many behavioural responses
have been associated with the techniques of intake of food, habits of feeding, rate of intake of
food, process of detecting food, as well as the choices for food. The primary factors, which may
influencing the feeding behaviour of fish, like the density of stocking, sex ratio, status of
reproduction, as well as biological rhythm, that have been used for the limited examination and
the results are often conflicting among and within the species. The endogenic clock mechanisms
that is responsible for controlling the periodic rhythms when it comes to feeding in fish.
However, environmental factors, like length of the day or temperature, can check others, or
function as the time setters as well as the synchronizers. The periodic feeding action, whether
founded on the various days, or weeks or even months is produced inside fish and degree of
feeding cycle that is influenced by the external elements is multifaceted. The major three rythms
of feeding within the fish that affect the use of food, are diel or daily, annual or seasonal, and
tidal or lunar cycles (Angotzi, Stefansson, Nilsen, Rathore & Rønnestad, 2013).
Therefore, the feeding cycle is produced endogenously by the help of a timing method
that is internal or by the biological clock. Hence, as it be might be expected for an actual watch
that in the absence of cues by the external time, circadian cycle exist-free-run-with its own
schedule, differing somewhat from the environmental rhythm where they usually coexist. The

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rhythms that are self-sustained normally exist for several periods devoid of dwindling, which
conflicts the rhythms that is hourglass-driven, which vanishes fast as soon as the external stimuli
stop. For example, if the cycle of feeding relied entirely on the physiological process of
hourglass, like the process gastric emptying or the rate of metabolism, the process of food intake
will cease under the conditions of fasting. Nonetheless, the activity of demand-feeding do not
vanish; thus, animals who are fasting ask for more food at the time which is favoured by them
(Ayada, Toru & Korkut Y. (2015).
The circadian system of fish has a pacemaker placed centrally in the brain along with at
least two oscillators that are peripheral situated in retina, as well as the pineal organ of the fish.
The structure of this system is compared fundamentally with the birds along with the mammals,
though some considerable differences persist. For example, the pineal organ of fish is a direct
photoreceptor that has a circadian cycle, which regulates the cyclic secretion of melatonin, as
well as changes the length of night into the Mel rhythms. This kind of hormone is directly entails
several physiological events that are rhythmic (for example, development and reproduction)
besides behaviour. The circadian system of fish plus other vertebrates is normally shown by a
“master” pacemaker that is placed centrally and functions as a synchronized of extensive
biological rhythms (Conde-Sieira, Chivite, Míguez & Soengas, 2018).
What endocrine control mechanisms may be controlling these feeding rhythms?
It has been found that the hypothalamus is a primary location for the regulation of
consumption of food inside the brain. Research has demonstrated that the endocrine system
regulates the feeding rhythms in fish. New fish appetite-regulating hormones have been

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examined. Thus, hormones are the messengers of various chemical produced inside the body,
which are liable for the interaction between diverse cell type, which accept their identity, as well
as act via the receptors that are structures which are proteinaceous in nature and are specialized
in the recognition of molecules. Following the closeness and the interaction between the
hormone-receptor, sequences of biochemical reacting resulting to specific biological responses
happen (Abbott & Volkoff, 2011). Food intake is controlled by major appetite-stimulating
(orexogenic) or appetite-inhibiting (anaroxeginic) endocrine factors that work on the centres
related to the feeding inside that of the brain to transfer the regulation of the short and the long-
term dietary intakes of the fish (Hevrøy et al., 2011). The endocrine factors emanate not only via
the CNS; however, also through the various peripheral organs, like the gastrointestinal (GI) tract,
liver, pancreas, as well as adipose tissue (Volkoff, 2016). The peripheral hormones mediate the
information to the feeding centres that are central either through the vagus nerve or via
overcoming the blood-brain barrier, as well as functioning directly via central receptors. Also,
the central peptides that comprise the orexigenic neuropeptide Y (NPY), and galanin, as well as
orexins besides the anorexigenic cocaine-and amphetamine-regulated transcript (CART) plus
corticotrophin-releasing hormone (CRH). The peptides related to the NPY are the most powerful
central promoters of hunger in fish. The NPY hormones in fish are extensively distributed in the
central nervous system and the fibres of NPY that are immunoreactive have been recognized in
the GI tract or the pituitary gland of multiple fish species. The greatest levels of NPYmRNA
have been located in the telencephalon-preoptic part in the hypothalamus plus the optic tectum
thalamus in goldfish. The NPY is the most powerful orexigenic agents in mammals. The
composition of the amino acid of the developed NPY peptide is comparatively well preserved in

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vertebrates, comprising fish, which show the same physiological roles in NPY (Barsagade et al.,
(2010).
Besides peptides, it has been found that there are molecules that help in signalling, such
as the hypothalamic monoamine neurotransmitters that are included in the regulation of the
intake of feed among fish. For instance, in goldfish, both the norepinephrine (NE) besides
dopamine (DA) have been confirmed to be entailed among the responses by the hypothalamus
due to starvation; noradrenergic system is stimulated and the dopaminergic system is stopped
through fasting. Additionally, the function of sensory inputs or the oral factors on the intake of
feed in the fish must be considered (Agnese, Valiante, Rosati, Andreuccetti & Prisco, 2016).
Question 3
How could activation of the stress response in aquaculture affect the neurohormonal
control of food intake?
In the past few years, considerable efforts have been made to explain the process that
regulates feed consumption among the fish. Hence, the suppression of feed consumption is a
genetic response in the fish ascribed to the acute or the chronic stress conditions where the fish
recovers from hunger when the stress factor vanishes. In multifaceted network that controls
hunger, the hypothalamus functions as a chief integrator of the endogenous peripheral, as well as
central afferent signals, which informs about the nutritional and energetic position of the fish
integrated to the arriving external outcomes (Cérda-Reverter, Agulleiro, Sánchez, Ceinos &
Rotllant, 2011).

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Temperature and the photoperiod are the two major factors of the environment that may
cause stress in fish in feeding. In aquaculture, fish will experience different adverse conditions,
for example, crowding, disturbing, confinement, aggression within the group, handling, low
quality of the water, as well as the timely feeding. The fish will response to this stress with
sequences of neuroendocrine changes, called stress response. Thus, several types of
environment, social, besides physical stresses inhibit the intake of feed, as well as affect the
behaviour of feeding (food searching, finding plus capture). Appetite has been seen as one of the
easily quantifiable indices in the health of fish; however, the methods of its regulation in fish is
treated to diverse stress factors that are not fine. Stress within the fish is an adaptable behaviour
whose ultimate aim is to attain internal homeostasis following an outer disturbance. The fishes
respond to this stress begins with the acknowledgement of an external stimulus (harmful)
resulting in the activation of different pathways, which affect fish physiology (Backstrom &
Winberg, 2013).
The two major neuroendocrine pathways in response to stress in fish include: the
hypothalamus-autonomous nervous system-catecholamine-generating chromaffin cells, as well
as the hypothalamus-pituitary-corticosteroid-generating internal cells. Corticotrophin-releasing
factors along with urotensin I (UI)-expressing cells of POA in addition to caudal neurosecretory
system are believed to be important donors to the control of stress response in fish. Thus, there is
increasing evidence that both corticotrophin releasing factor (CRF) and urotensin I (UI) can be
the mediators that act endogenously for the stress-induced suppression of the intake of the feed
as identified in the fish. In the goldfish, for instance, the administration of CRF prompts the time
and the dose-reliant suppression in regard to the consumption of food, which shows that CRF can

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have a role in the primary control of feeding in the fish. Intracerebroventricular administrations
using both CRF and UI in goldfish have shown a dose-dependent suppression in feeding in fish.
Diverse environmental along with social factors have been demonstrated to show the increase in
the CRF mRNA in the POA rainbow trout. CRF fibres will release their components adjacent to
the corticotrophins in the neurohypophysis where adrenocorticotropin (ACTH) is generated from
its precursor-proopiomelanocortin (POMC). On the other hand, adrenocorticotropin triggers
secretion of cortisol from the internal cells. Research has shown that the POMC-derived peptide
from the melanotrophs of neurointermediate lobe of the pituitary or MSH along with endorphin-
associated peptides may acknowledge to the stress in fish. In addition, the stress response of
corticotrophes, as well as melamotrophs can be reliant on the kind of stressor in question.
Hybridization related studies have shown that the expression of POMC mRNA in the
hypothalamic regions linked to neuroendocrine control of feed intake. Also, CRF-related
peptides along with melanocortins can be implied in different appetite-controlling mechanisms.
Hence, it seems that melanocortin peptides may take part in the appetite regulation in fish as
anorexigenic factors (Gambardella et al., 2012).
Additionally, the pharmacological studies show that the CRF and its neuropeptide partner
UI generate an anorexigenic impact in the fish. The CRF plus UI are generally acknowledged as
primary controllers of the anorexigneic stress respond in fish, in which central dosage of UI
prompts an anorexigenic effect is even more powerful as compared with the impact enhanced by
the CRF treatment. Also, the effect of this kind of treatment in fish is inhibited by the injection of
an antagonist of UI besides the CRF receptor that suggests that the neuropeptides are directly
connected to inhibition of the food intake in fish. Further to this, UI and CRF controls the

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existence of ACTH that acts downstream of the melanocortin system, which is the chief
promoter for the release of cortisol. Studies have reported that the chronic treatment together
with acute cortisol treatments exerts a powerful anorexigenic effect on fish. Further, cortisol
appears to be also engaged in maintaining the anorectic response in fish, with particular
glucocorticoid receptors functioning as mediators (Cerda-Reverter & Canosa, 2009).
Additionally, in fish similar to the remaining vertebrates, the monoamine
neurotransmitters like 5-HT, DA, and NE plays a leading function in the response to the stresses
that is linked to behavioural differences. For example, the rainbow trout is subjected to the social
stress is responded with a low intake of food, while higher release and turnover of the 5HT,
dopamine and the NE along with their metabolites that is presented in these fish brain showed
greater neural activity. Hence, the primary action of 5HT has been incorporated in the process of
food regulation in fish that is put through stress. In addition, the functional interaction among
CRF and hypothalamic catecholaminergic system in the major regulation of the feed intake has
been recorded. Though the function of insulin in the intake of food is regulated in fish is unclear,
evidence exist concerning an anorexigenic effect in the hormone. Hence, intraperitoneal
administration of insulin in the rainbow trout lowered the intake of food while isletectomy in the
goby induces hyperphagia (Fuentes, Safian, Einarsdottir, Valdes, Elorza & Molina, 2013).
Question 4
The control of the intake of feed is very multifaceted process. The meal cycles have
substantial effect on fish physiology and behaviour. If the food is given for fish on the everyday
basis at same time, fish would concur to the mealtime and then develop higher activity in an

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expectancy of the forthcoming meal. The homeostatic control of food consumption depends on
the multifaceted network involved in the peripheral or the central signals that are incorporated in
hypothalamus which in turn respond with the delivery of the orexigenic or the anorexigenic
neuropeptides which gradually promote or inhibit the appetite. Hence, under the conditions of
stress, the procedure that manage the consumption of food within fish are not regulated and the
hunger signal inside the brain do not function as in controlled conditions that leads to the
changes in the expression of the appetite-related neuropeptides and also reduce food ingestion.
The impact of stress on various processes that control the intake of food in the fish that seems to
be transmitted in part by the corticotropin-releasing factor (CRF), an anorexigenic neuropeptide
related in the establishment of the HPI axis in the physiological stress response. Moreover, the
melanocortin system is as well engaged in the association between the HPI axis and the central
control of food (Babichuk & Volkoff, 2013).
In general, hunger triggers the feeding behaviour in the fish. When the feed is provided,
fish can start feeding at an instantaneous rate, and is slowly decreased or stopped with a decrease
of appetite over time. The environmental factors, like the velocity of water, temperature, light,
predators, social factors, as well as the disturbance by human beings, can also affect the fish
feeding behaviour. The feeding practices, like the similar distribution of feed into water, may
affect the chances of the fish of gaining access to the food materials that is being offered. Thus,
there may be many summations of all the biotic along with the abiotic factors, which may have a
significant impact on the feeding behaviour of fish. In many instances, fish often stop eating for
no obvious reason and the rates of feeding might be either disease or rise in numbers over time.
A better understanding of all the factors, which may affect feeding might permit for the better

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management of the feed and the allocation of the food to the fish, and lower the differences in
the feeding plus growth rates, which are normally evident amongst individuals or amongst
groups of fish (Baltzegar, Reading, Douros & Borski, 2014).
It is usually recognized that the fish need to feed in order to satisfy their energy needs.
Fishes that are fed on a diet with the low energy content are compelled to boost their rate of
consumption and the rate of gastric evacuation in order to compensate for the reduced caloric
diet. The other nutrients also affect the intake of feed in fish; nonetheless, with anorexia being a
widespread factor of almost all the nutrient deficiencies. The size of the particle is closely
connected to the food intake in fish whereby the correct food particle size generates positive
behavioural response. The particles of feed must be adequately tiny in order for the fish to ingest,
whilst being large enough to be taken without using too much energy in the process (Amiya,
Mizusawa, Kobayashi, Yamanome, Amano & Takahashi, 2012).
To increase the efficacy of the farming systems, especially aquaculture, there is a need to
proper food management along with the culture of effective management of the system. To boost
efficiency in the management of food in aquaculture, there is a need of predicting the intake of
food plus the growth under a broad range of environmental along with the cultural conditions.
Many environmental, and physiologic, as well as genetic factors that have been acknowledged
that related to feed intake and are believed to be regulators of feed intake. When food availability
is limitless, the quantity of food consumed is called the voluntary feed intake (VFI). Thus, one
primary character of the VFI is description of the regulatory feedback process that is not clearly
known in most of the fish. Specifically, recognition of many controlling signals and their
incorporation into the specific responses might eventually control feeding behaviour in fish.

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Biotic factors, which include size of the fish, physiologic stage, as well as genotype, are known
to influence VFI. Amongst the environmental factors, both the temperature and water and the
photoperiod control the consumption of food. Hence, food intake is also under the close
neuronal, metabolic, and endocrine control, all of which are closely connected to the nutritional
state of the animal. Many methods are accessible to monitor the individual food intakes and the
passages of feed via the alimentary tract (Gahete et al., 2009).