Ivar Rønnestad

University of Bergen | UiB · Department of Biological Science

Episodes of elevated temperature, combined with lower feed availability, are among the predicted scenarios of climate change representing a challenge for coral reef fish. We investigated the response of clownfish (Amphiprion ocellaris) to a scenario in which it received a single meal to satiety after 48 h fasting at 32 °C (climate change scenario)...

During the first feeding period, fish will adapt to exogenous feeding as their endogenous source of nutrients is depleted. This requires the development of a functional physiological system to control active search for food, appetite, and food intake. The Atlantic salmon (Salmo salar) melanocortin system, a key player in appetite control, includes...

Aquaculture of Atlantic salmon Salmo salar is in transition to precision fish farming and digitalization. As it is easier, cheaper and safer to study a digital replica than the system itself, a model of the fish can potentially improve monitoring and prediction of facilities and operations and replace live fish in many what‐if experiments. Regulato...

As most fish are ectotherms, their physiology is strongly affected by temperature. Temperature affects their metabolic rate and thus their energy balance and behavior, including locomotor and feeding behavior. Temperature influences the ability/desire of the fish to obtain food, and how they process food through digestion, absorb nutrients within t...

An organism’s biological processes are adapted to and driven by rhythmicity in the natural environment and periodicity of light is one of the most influential factors. In a developing organism, the onset of circadian rhythmicity might indicate the time point of functional necessity for aligning processes to the environment. Here, the circadian cloc...

We compared the performance and physiological response of diploid and triploid Atlantic salmon (Salmo salar) following 21 days of either unpredictable chronic stress (UCS) or no disturbance (control). Thereafter, all four groups were challenged with a novel acute stressor consisting of crowding, netting and transfer into another tank. Growth was mo...

In teleosts, two PepT1-type (Slc15a1) transporters, i.e., PepT1a and PepT1b, are expressed at the intestinal level. They translocate charged di/tripeptides with different efficiency, which depends on the position of the charged amino acid in the peptide and the external pH. The relation between the position of the charged amino acid and the capabil...

This study aimed to determine the impact of elevated temperature combined with different levels of dietary methionine concentrations on feed intake (FI) and brain expression of selected neuropeptides and one receptor involved in appetite control in juvenile cobia (approximately 3.7 g body weight). The genes studies were neuropeptide y, npy; agouti-...

In mammals, the main center for appetite control is the arcuate nucleus (ARC), which contains different neuronal populations. Anorexigenic neurons co-express cocaine- and amphetamine-regulated transcript ( cart) and proopiomelanocortin ( pomc) neuropeptides. The pomc peptide undergoes posttranslational modifications and one of its products, α-MSH,...

Taurine is a sulphur-containing amino acid with important physiological roles and a key compound for the synthesis of bile salts, which are essential for the emulsion and absorption of dietary lipids. This study aimed to evaluate the effects of taurine supplementation to low-fishmeal diets on the metabolism of taurine, bile acids, and lipids of Sen...

Precision feeding aims to provide the correct amount of feed to farmed animals for optimal growth and performance and to avoid feed waste. However, knowledge underlying the meal-to-meal variability in voluntary feed intake of farmed species is still limited. This study examined the relationship between meals, feed deprivation time and the feed (pel...

In the present study, polyethylene (PE) microplastics (150–300 μm) were added to Atlantic cod (Gadus morhua) feeds at 1 %, either in their present form (Virgin PE) or spiked with PCB-126 (Spiked PE). The feeds were given to juvenile cod for a 4-week period. The fish grew from 11 to 23 g with no significant difference between dietary treatments. Cod...

Atlantic salmon will experience periods of fasting during its lifecycle. In nature, prolonged fasting periods occur owing to seasonal fluctuations in available feeds, migration or in relation to reproduction. In a culture setting, salmon is fasted mainly as part of planned operational handling prior to vaccination, delousing, transfer etc., and whe...

Atlantic salmon will experience periods of fasting during its lifecycle. In nature, prolonged fasting periods occur owing to seasonal fluctuations in available feeds, migration or in relation to reproduction. In a culture setting, salmon is fasted mainly as part of planned operational handling prior to vaccination, delousing, transfer etc., and whe...

Leucine has been identified to modulate feed intake and energy homeostasis in fish as in other vertebrates. Under allostatic conditions, energy expenditure may change, and adjustments to the processes that govern the energy homeostatic system may be necessary. We investigated the responsiveness of appetite-related neuropeptides involved in feed int...

Zebrafish (Danio rerio) is a well-established animal model, used in a number of research areas. In the last decade, it has also emerged as a tool to evaluate the effects of diets and dietary components and to test novel paradigms in nutrigenomics, nutrigenetics, and nutritional physiology. Despite its worldwide use, the standardization of the zebra...

The melanocortin system is a key regulator of appetite and food intake in vertebrates. This system includes the neuropeptides neuropeptide y (NPY), agouti-related peptide (AGRP), cocaine- and amphetamine-regulated transcript (CART), and pro-opiomelanocortin (POMC). An important center for appetite control in mammals is the hypothalamic arcuate nucl...

We studied molecular effects (RNAseq and qPCR) of first feeding prey types (copepods or rotifers/Artemia) on skeletal muscle myogenesis and growth dynamics (proliferation, differentiation), metabolism (glycolysis, gluconeogenesis, oxidative phosphorylation), and antioxidant defense system (production/regulation of reactive oxygen species (ROS) in c...

Episodes of elevated temperature, combined with lower feed availability, are among the predicted scenarios of climate change and represents a challenge for coral reef fish. We mimicked two scenarios to explore the short- and long-term response of clownfish (Amphiprion ocellaris) with regards to feed intake, growth, metabolic rate; and expression of...

We have described six developmental stages for the ballan wrasse, from the first feeding until the juvenile stage, supported by specific descriptions of cranial ossification, maturation of the digestive tract, and growth‐correlated stages. The initial formation and development of bones are closely linked to the functional anatomical structures requ...

The high‐affinity/low‐capacity system Slc15a2 (PepT2) is responsible for the reuptake of di/tripeptides from the renal proximal tubule, but it also operates in many other tissues and organs. Information regarding PepT2 in teleost fish is limited and, to date, functional data are available from the zebrafish (Danio rerio) only. Here, we report the i...

Warm water treatment has in recent years become widely used for ridding salmonids of sea lice in aquaculture although the consequences of the treatment for fish welfare are not adequately investigated. The objective of this study was to document potential long-term welfare effects of repeated warm water treatments on Atlantic salmon (Salmo salar)....

The high-affinity/low-capacity system Slc15a2 (PepT2) is responsible for the reuptake of di/tripeptides from the renal proximal tubule, but it also operates in many other tissues/organs. Information regarding PepT2 in teleost fish is limited and to date functional data are available from the zebrafish ( Danio rerio ) only. Here, we report the ident...

The aim of the current trial was to test whether leucine affected growth and accretion including test any effects on leucine upon stress. Quadruplicate tanks each containing 50 Atlantic salmon (Salmo salar) (mean start body weight of 524 ± 28 g) were fed diets containing 27.3, 30.0, 35.0 and 41.0 g leucine/kg diet for 74 days. Two tanks per dietary...

System b 0,+ absorbs lysine, arginine, ornithine, and cystine, as well as some (large) neutral amino acids in the mammalian kidney and intestine. It is a heteromeric amino acid transporter made of the heavy subunit SLC3A1/rBAT and the light subunit SLC7A9/b 0,+ AT. Mutations in these two genes can cause cystinuria in mammals. To extend information...

Cocaine- and amphetamine-regulated transcript (CART) has been known to be involved in feeding and energy balance in mammals, acting as an anorexigenic neuropeptide in hypothalamus. In Atlantic salmon, little is known about Cart brain localization and its function. In this study, in silico analysis revealed the existence of 10 cart paralogs, here na...

Control of appetite and feed intake in fish larvae are still largely unexplored. Two of the key players in controlling vertebrate's feed intake are cholecystokinin (CCK) and peptide YY (PYY). Here we investigated the mRNA expression of pyy, cck and cck receptors (cckr) in the brain (head) and gut of Atlantic halibut larvae in response to three cons...

Neuropeptide Y (NPY) is known as a potent orexigenic signal in vertebrates, but its role in Atlantic salmon has not yet been fully established. In this study, we identified three npy paralogs, named npya1, npya2, and npyb, in the Atlantic salmon genome. In silico analysis revealed that these genes are well conserved across the vertebrate’s lineage...

Sensing of amino acids in fish brain, especially branched-chain amino acids (BCAA) like leucine, is involved in regulation of feed intake through different mechanisms. However, there is limited information regarding the possible involvement of mechanisms dependent on amino acid carriers of the solute carrier families (SLC) known to be key regulator...

Corticotropin-Releasing Factor (CRF) is one of the main mediators of the Hypothalamic-Pituitary–Interrenal (HPI) axis to stress response. In Atlantic salmon, a comparative understanding of the crf1 paralogs role in the stress response is still incomplete. Our database searches have identified four crf1 genes in Atlantic salmon, named crf1a1, crf1a2...

Food intake is a vital process that supplies necessary energy and essential nutrients to the body. Information regarding luminal composition in the gastrointestinal tract (GIT) collected through mechanical and nutrient sensing mechanisms are generally conveyed, in both mammals and fish, to the hypothalamic neurocircuits. In this context, ghrelin, t...

In the present study, two salmon feeds with different disintegration stabilities were produced by impacting extruder viscous heat dissipation with the use of different lipid levels in the feed mix. The feeds were then dried and coated to similar final lipid levels (32%) and nutritional composition. Both feeds were produced as 4 and 6-mm pellets. Fe...

In mammals, knockout of LEPR results in a hyperphagic, morbid obese, and diabetic phenotype, which supports that leptin plays an important role in the control of appetite and energy metabolism, and that its receptor, LEPR, mediates these effects. To date, little is known about the role(s) of lepr in teleost physiology. We investigated a zebrafish (...

Warm water treatment, i.e. exposure to sea water at a temperature of 28–34 °C for 20–30 s, has in recent years been widely used for delousing of Atlantic salmon (Salmo salar) and rainbow trout (Oncorhynchus mykiss) in Norwegian aquaculture. High mortality and various lesions (e.g. injuries and/or bleedings in skin, fins, eyes, brain, and gills) hav...

The effects of nutrient and mechanical sensing on gut motility and intestinal metabolism in lower vertebrates remains largely unknown. Here we present the transcriptome response to luminal stimulation by nutrients and an inert bolus on nutrient response pathways and also the response on gut motility in a stomachless fish with a short digestive trac...

The clown anemonefish (Amphiprion ocellaris) is a common model species in studies assessing the impact of climate changes on tropical coral fish physiology, metabolism, growth, and stress. However, the basic endocrine principles for the control of food intake and energy homeostasis, under normal and elevated sea temperatures, in this species remain...

The influence of diurnal and nocturnal feeding on daily rhythms of gut levels of cholecystokinin (CCK) and the activity of two key pancreatic proteases, trypsin and chymotrypsin, were examined in juveniles of Senegalese sole (Solea senegalensis), a species with nocturnal habits. Four feeding protocols were performed: P1) One morning meal; P2) Six m...

Cationic amino acid transporter 1 (Cat-1 alias Slc7a1) is a Na⁺-independent carrier system involved in transport and absorption of the cationic amino acids lysine, arginine, histidine, and ornithine and has also been shown to be indispensable in a large variety of biological processes. Starting from isolated full-length zebrafish (Danio rerio) cDNA...

A tube-feeding model for administering microplastic (MP, Ø = 30 μm) spheres to fish larvae was employed to quantify the uptake of hydrophobic organic contaminants (HOCs) into the larval body through a single administration of MP. Polychlorinated biphenyl-153 (PCB-153) was used as a representative HOC that can be sorbed to MP in the sea. Atlantic he...

The melanocortin system is a key neuroendocrine network involved in the control of food intake and energy homeostasis in vertebrates. Within the hypothalamus, the system comprises two main distinct neuronal cell populations that express the neuropeptides proopiomelanocortin (POMC; anorexigenic) or agouti-related protein (AGRP; orexigenic). Both bin...

Ongoing global warming is one of the major challenges for the development of aquaculture in the tropical regions where species are already cultured in the water temperature close to their upper physiological thresholds. Furthermore, warming can trigger blooms of toxic algae, yet we do not know how extreme warming such as a marine heatwave (MHW) and...

The orexigenic agouti-related protein (AgRP) and the anorexigenic pro-opiomelanocortin (POMC) are crucial players in the control of feed intake in vertebrates, yet their role in teleosts has not been fully established. Triplicate groups of Atlantic salmon (Salmo salar) post smolts were subjected to (1) fasting for 3 days (fast) and (2) normal feedi...

Following publication of the original article [1], the authors flagged that the ‘Availability of data and materials’ declaration is incomplete.

Background: Peptide transporter 1 (PepT1, alias Slc15a1) mediates the uptake of dietary di/tripeptides in all vertebrates. However, in teleost fish, more than one PepT1-type transporter might function, due to specific whole genome duplication event(s) that occurred during their evolution leading to a more complex paralogue gene repertoire than in...

The transcriptome of nutrient sensing and the regulation of gut motility by nutrients in a stomachless fish with a short digestive tract; the ballan wrasse ( Labrus berggylta ) were investigated. Using an in vitro model, we differentiate how signals initiated by physical stretch and nutrients modulate the gut evacuation rate and motility patterns,...

Peptide Transporter 1 (PepT1) mediates the uptake of dietary di/tripeptides in vertebrates. But, in teleost fish gut more than one PepT1-type transporter might operate, due to teleost-specific whole gen(om)e duplication event(s) occurred during evolution. Here, we describe a novel teleost di/tripeptide transporter, i.e. the Atlantic salmon (Salmo s...

Active Learning Pedagogy has been shown to be a highly effective instructional strategy for teaching in STEM courses. However, the majority of evidence supporting this finding has had a strong North American bias, with relatively little work exploring how faculty and students from different cultural backgrounds interact with active learning. Conseq...

Cholecystokinin (CCK) is well-known as a key hormone that inhibits stomach emptying and stimulates midgut motility in gastric species. However, the function of CCK related to gut motility in agastric fish, especially in fish with a short digestive tract such as ballan wrasse, remains unknown. Here we present a detailed description of the spatio-tem...

The present study is focused to elucidate the main characteristics of the digestive function of this carnivorous fast-growing fish living at high temperatures. With this aim, we have examined the effects of an increased temperature from 30 to 34 °C on the daily pattern of gastrointestinal pH, enzymatic proteolytic digestive activity and the feed tr...

The cover image, by Minh Van Nguyen et al., is based on the original article The role of dietary methionine concentrations on growth, metabolism and N‐retention in cobia (Rachycentron canadum) at elevated water temperatures. DOI: 10.1111/anu.12875.

The physiological mechanisms that control food intake in the brain of mammals consist of orexigenic and anorexigenic neuronal populations that integrate both central and peripheral signals and play a pivotal role on the control of appetite. The neuropeptide Y (NPY) and agouti‐related proteins (AgRP) are neuropeptides expressed and secreted by the o...

The G protein‐coupled receptor family C, group 6, member A (GPCR6A) and the calcium‐sensing receptor (CaSR) belong to the GPCRs family C and play a crucial role in sensing amino acids in the mammalian gastrointestinal (GI)‐tract. These receptors, located in the enteroendocrine cells facing the GI‐tract lumen, are activated by dietary amino acids, w...

In vertebrates, G protein–coupled receptors (GPCRs) detect the sweet, umami and bitter tastes. The sweet and umami GPCRs are encoded by the T1R gene family, whose members heterodimerise to detect molecules associated with sweet (T1R2‐T1R3) and umami (T1R1–T1R3) tastes. The bitter receptors are encoded by the T2R gene family. In mammals, these recep...

In contrast to most other teleosts studied to date, salmonids has undergone four whole genome duplications (WGD), commonly referred to as the Ss4R (salmonids-specific 4th vertebrate WGD) event. Large genomic rearrangements and the restoring of the disomic chromosome inheritance in the ancient polyploidy have been crucial for the post Ss4R rediplodi...

Amino acids and small peptides in the form of di/tripeptides are key nutrients in animal diets and essential contributors to growth. In mammals, di/tripeptides represent a highly significant fraction of dietary protein after digestion and are transported across the brush‐border membrane of the intestinal epithelium via a single transport protein, t...

In contrast to most other teleosts studied to date, salmonids has undergone four whole genome duplications (WGD), commonly referred to as the Ss4R (salmonids‐specific 4 th vertebrate WGD) event. Large genomic rearrangements and the restoring of the disomic chromosome inheritance in the ancient polyploidy have been crucial for the post Ss4R re‐diplo...

To characterize the effects of a plant-based low-fishmeal (LFM) diet on the digestive physiology of yellowtail, Seriola quinqueradiata, we prepared two isonitrogenous and isolipidic diets; an FM-based diet (diet Control, FM 50%) and a plant protein (soybean meal and corn gluten meal)-based low fishmeal diet (diet LFM, FM 15%), and examined the acut...