Chronic renal failure (CRF) is defined as a loss of kidney function or structural damage lasting for more than three months, regardless of the cause [1]. The rate of CRF is 15% worldwide [2]. The number of patients receiving renal replacement therapy (RRT) in Turkey was 83783 in 2019 [3]. According to the “United States Renal Data System”, Turkey is among the ten countries with the highest increase in end-stage renal disease (ESRD) between 2003 and 2016 [2]. Since the kidneys cannot function normally and excrete metabolic waste products in ESRD, each patient needs hemodialysis treatment, which lasts approximately three to 4 h three times a week on average [4]. The rate of patients who received HD treatment in Turkey was 73.2% in 2019, and 713 patients undergoing hemodialysis treatment died [3].

Despite the benefits of hemodialysis treatment, patients may develop physical and psychosocial problems and symptoms [[5], [6], [7]]. Undesirable symptoms experienced by patients undergoing hemodialysis include hypotension/hypertension, respiratory distress, headache, back-chest pain, muscle cramps, nausea-vomiting, fatigue, fever, constipation, diarrhea, and itching [5,7,8]. Hemodialysis can also cause negative emotions such as anger, anxiety, unhappiness, fear [9], adjustment disorder, anxiety [10], depression [11], and sleep disorders [12], and patients may experience social isolation due to the fear of burdening their family members [13,14] and loneliness [15]. The physical symptoms that patients under hemodialysis treatment are supposed to cope with, and psychological symptoms like unhappiness and loneliness make it challenging to adapt to the disease and contribute to an increase in mortality [16].

Today, “pet therapy” is used as a treatment in many hospitals, psychiatry clinics, nursing homes, and rehabilitation centers. Pet therapy is an application in the Nursing Interventions Classification [17,18]. Various studies with different animals and populations in health services, hospitals, psychiatry clinics, nursing homes, and rehabilitation centers showed that pet therapy has physiological and psychological benefits such as a reduction in psychiatric signs and symptoms, increase in cardiovascular system functionality, socialization skills and individual self-management [19,20]. The physiological and psychological benefits of pet therapy applications have been proven in various studies using some animals (such as birds, dogs, cats, and fish) and robot simulations [[21], [22], [23], [24], [25], [26]]. Robotic pet therapy reduces depression [21], agitated behaviors, pain [21,23], stress hormone levels, and loneliness and increases heart rate [23], happiness [22], and quality of life [24]. Even a simple movement of live animals reduces the feeling of loneliness, anxiety, depression, and social isolation [25,26].

An unpublished experimental doctoral thesis study, a poster statement of which can be reached, was conducted abroad on “the effect of pet therapy with live dogs on depression” in patients with CRF [27]. A pilot study and a pre-test-post-test study examined the effect of pet therapy on happiness with a live dog [28,29]. In Turkey, no study, to our knowledge, has investigated the effect of pet therapy in patients undergoing CRF and hemodialysis. However, there is a paucity in the literature on the benefits of human-fish interactions related to pet therapy. Ornamental betta fish has been reported to increase individual self-management [19] and reduce anxiety and stress [30]. A systematic review demonstrated that various fish species reduced anxiety, physiological stress, anxiety, and pain, provided relaxation, improved food intake, and had positive benefits on mood and body weight (weight gain), but no information was found about loneliness [31].

Only pet therapy with live dogs has been used in hemodialysis patients, but no experimental study has been performed and no information has been found on the effect of Betta fish therapy on loneliness, happiness, dialysis symptoms, compliance with ESRD, and body mass index (BMI) in patients undergoing hemodialysis. The fact that the above-mentioned parameters were not examined shows a lack of evaluation of robotic cat or Betta fish therapies. After all these considerations, this study aimed to investigate the positive physiological (dialysis symptoms, BMI) and psychological (dialysis symptoms, happiness, loneliness, and adherence to ESRD) effects of robotic cat and Betta fish therapies in patients undergoing hemodialysis.