Effects of structural environmental enrichment on welfare of juvenile seabream (Sparus aurata)

Current production systems of finfish aquaculture, and in particular intensive farming systems, can cause welfare problems leading not only to poor condition of the fish but also to a decrease in product quality. Adding structural environmental enrichment (EE) to bare rearing environments may improve the welfare of certain cultured fish. In this study we experimentally demonstrate the positive effects of adding structural EE on rearing environments of juvenile seabream (Sparus aurata). Fish maintained for 35 days with EE showed less aggression and interactions with the net pen, and lower erosion of pectoral and caudal fins, compared to fish kept in bare conditions (non-enriched, NE). In addition, EE modified the horizontal distribution of fish in the experimental cage, increasing the use of the inner areas. Non-significant effects of EE were observed on fish body condition and growth, and on brain monoamines levels and mortality. Nevertheless, this work highlights the potential use of structural EE to improve welfare of juvenile seabream, which might be feasible to apply at larger-commercial scale.Agência financiadora Aquicultura Balear S.A.U (Grupo Culmarex) Portuguese Foundation for Science and Technology UID/Multi/04326/2019 Spanish national funds from MINECO (R+D project: PHENOFISH) CTM2015- 69126-C2-1-Rinfo:eu-repo/semantics/publishedVersio

Cellular and molecular mechanisms of immunomodulation in the brain through environmental enrichment

Recent studies on environmental enrichment (EE) have shown cytokines, cellular immune components [e.g., T lymphocytes, natural killer (NK) cells], and glial cells in causal relationship to EE in bringing out changes to neurobiology and behavior. The purpose of this review is to evaluate these neuroimmune mechanisms associated with neurobiological and behavioral changes in response to different EE methods. We systematically reviewed common research databases. After applying all inclusion and exclusion criteria, 328 articles remained for this review. Physical exercise (PE), a form of EE, elicits anti-inflammatory and neuromodulatory effects through interaction with several immune pathways including interleukin (IL)-6 secretion from muscle fibers, reduced expression of Toll-like receptors on monocytes and macrophages, reduced secretion of adipokines, modulation of hippocampal T cells, priming of microglia, and upregulation of mitogen-activated protein kinase phosphatase-1 in central nervous system. In contrast, immunomodulatory roles of other enrichment methods are not studied extensively. Nonetheless, studies showing reduction in the expression of IL-1β and tumor necrosis factor-α in response to enrichment with novel objects and accessories suggest anti-inflammatory effects of novel environment. Likewise, social enrichment, though considered a necessity for healthy behavior, results in immunosuppression in socially defeated animals. This has been attributed to reduction in T lymphocytes, NK cells and IL-10 in subordinate animals. EE through sensory stimuli has been investigated to a lesser extent and the effect on immune factors has not been evaluated yet. Discovery of this multidimensional relationship between immune system, brain functioning, and EE has paved a way toward formulating environ-immuno therapies for treating psychiatric illnesses with minimal use of pharmacotherapy. While the immunomodulatory role of PE has been evaluated extensively, more research is required to investigate neuroimmune changes associated with other enrichment methods.Gaurav Singhal, Emily J. Jaehne, Frances Corrigan and Bernhard T. Baun

Modifications of surrounding environment to improve intensive rearing of gilthead seabream Sparus aurata

Environmental enrichment is defined as “an improvement in the biological functioning of captive animals resulting from modifications to their environment” and may provide for the psychological and behavioral needs of captive animals. The majority of the studies on the effect of environmental enrichment on fish focused on environmental complexity effects. For example, tanks containing live or plastic plants, several kinds of substrate or even novel objects improved the fitness and foraging behavior of hatchery-produced fish when released in the wild, thus increasing their chances of survival and success of re-introduction programs. On the other hand, structurally enriched tanks reduced, increased or had no effect on the aggressive behavior of several widely reared species. Moreover, environmental enrichment resulted in improved growth or survival for several fish species, but had no growth effect on other fish species. From another point of view, increased environmental complexity may enhance the cognitive abilities of other vertebrates and fish. Especially in the case of fish, environmental modifications affected brain size and brain cell proliferation which may contribute to a more flexible behavior and improved cognitive and learning abilities.The aim of the present Thesis is to investigate whether the modification of surrounding environment of gilthead seabream Sparus aurata may act as a means of environmental enrichment and thus improve its intensive rearing. For this purpose, five experiments were designed and performed.In the first experiment it was shown that gilthead seabream (age 1+) reared (84 days) with Blue or Red-Brown substrate (BS and RBS respectively) improved their growth performance (mass, total and standard length, Specific Growth Rate, Mass Gain) and feed utilization (Food Conversion Ratio). Besides, BS fish presented better Condition Factor (CF) and higher content of n-3 polyunsaturated fatty acids in the fillet than fish from other treatments. Moreover, lower level of aggression was observed for BS and RBS fish, which also showed certain alterations in brain monoamine neurotransmitters levels. Fish-bottom interactions were observed in all treatments regardless the presence of substrate. On the other hand, the overall performance of fish reared with Green substrate (GS) was hardly differentiated from fish reared in tanks without substrate (no-substrate, NS). Physiological status of fish as estimated by plasma and liver parameters examined was similar among treatments. Τhe second experiment investigated whether the beneficial effects of the presence of Blue or Red-Brown substrates could be still apparent when gilthead seabream is reared under different densities (98 days). In this experiment fish of different progeny and age (0+) were used. According to results BS fish had better growth performance (body mass, Specific Growth Rate, Mass Gain), reduced aggressive behavior, better fillet quality (n-3 polyunsaturated fatty acids content) and brain monoamine neurotransmitters alterations. On the other hand, RBS fish presented the same results as BS fish but failed to produce significant growth enhancement. Physiological status of fish was not affected by treatments (blood and liver parameters, carcass proximate composition).In the first two experiments, the response of gilthead seabream to the chosen substrates was studied. The aim of the third experiment was to “ask” gilthead seabream if and what substrate it chooses. For this purpose, preference tests of paired choices were performed. Treatments included the three substrates used in previous experimentation and the plain environment (no-substrate). Preference tests were conducted for two age classes (2+ and 0+) to account for previous long term experiments and fish were tested either individually or in groups of seven specimens in order to evaluate the possible involvement of sociality on fish preferences. In contrasts of the three substrates with NS, a clear choice for BS and RBS and an insistent rejection of the GS was observed for fish of both age classes. In dual substrate contrasts older fish chose BS over RBS or GS while they preferred RBS only when BS was not present. On the other hand, younger fish made no choice between BS and RBS or GS while they preferred RBS over GS. According to results fish choices were quite similar no matter if fish were tested individually or in groups.Given the results of the three previous experiments, the following experimentations were focused on the BS. The aim of the forth experiment was to elucidate whether the color of the BS used or its physical presence is responsible for the observed enrichment effects, as well as the possible involvement of the photic environment on results. For this purpose, 0+ fish were reared in tanks with BS, with the photo of the blue substrate on the bottom (PBS) or in NS. According to results, BS fish showed improved growth performance (mass, Specific Growth Rate) and food utilization (Food Conversion Ratio) and presented the lower level of aggression. Blood parameters and retina structure were not affected by treatments. Performance of fish reared with PBS was not differentiated from that of NS fish.The aim of the fifth experiment was to investigate the possible effect of BS on gilthead seabream stress response. The experiment was designed to study the effect of confinement stress and fish recovery through primary and secondary stress response indicators. To this end, fish (age 0+) were reared (75 days) with or without BS and then subjected to confinement stress for 30, 60 or 90 minutes. Fish recovery to normal conditions was also examined after 2, 6 and 24 hours post-stress. According to results, fish reared with BS presented better growth performance and reduced aggressive behavior than fish in NS tanks. Moreover, BS did modify the time course of gilthead seabream stress response to confinement.In conclusion, the overall results of the present Thesis showed and confirmed that the presence of blue substrate, and not only its color, was beneficial for the intensive rearing of gilthead seabream, since it improved both productive-related and behavioral traits and modified fish social interactions. The use of the blue substrate as an effective means of environmental enrichment, improving fish welfare, is further supported by the fact that gilthead seabream preferred the blue substrate. It is considered encouraging that a rather simple improvement of fish rearing environment (as the substrate used) may have multiple beneficial aspects for fish and producersΟ εμπλουτισμός του περιβάλλοντος ορίζεται ως η τροποποίηση εκείνη του περιβάλλοντος διαβίωσης η οποία έχει ως αποτέλεσμα τη βελτίωση των βιολογικών λειτουργιών των ζώων που βρίσκονται σε αιχμαλωσία και αποσκοπεί στην εξασφάλιση των «ψυχολογικών» αναγκών των ζώων αλλά και στην έκφραση της φυσικής τους συμπεριφοράς. Η πλειοψηφία των εργασιών που σχετίζονται με την επίδραση του εμπλουτισμού του περιβάλλοντος στα ψάρια επικεντρώνεται στην εφαρμογή ενός πιο σύνθετου περιβάλλοντος. Για παράδειγμα, έχει παρατηρηθεί ότι η προσθήκη ζωντανών ή πλαστικών φυτών, διαφόρων ειδών υποστρωμάτων ή ακόμα και η εισαγωγή νέων αντικειμένων βελτιώνουν την ικανότητα ανεύρεσης τροφής των εκτρεφόμενων ψαριών που προορίζονται για απελευθέρωση στο φυσικό περιβάλλον, ενώ αυξάνονται οι πιθανότητες επιβίωσης των ψαριών μετά την απελευθέρωσή τους. Επιπλέον, η διαφοροποίηση του περιβάλλοντος μπορεί να αυξήσει, να μειώσει ή να μην επηρεάσει την επιθετική συμπεριφορά διαφόρων ειδών εκτρεφόμενων ψαριών και να βελτιώσει ή να μην έχει επίδραση στην ανάπτυξη. Ο εμπλουτισμός του περιβάλλοντος μπορεί επίσης να βελτιώσει την ικανότητα αντίληψης Θηλαστικών αλλά και των ψαριών. Ειδικά στην περίπτωση των ψαριών, η διαφοροποίηση του περιβάλλοντος επηρεάζει το μέγεθος και τον κυτταρικό πολλαπλασιασμό του εγκέφαλου, που μπορεί να συμβάλλουν σε μια πιο εύπλαστη συμπεριφορά και καλύτερη ικανότητα αντίληψης και μάθησης.Σκοπός της παρούσας μελέτης είναι να διερευνηθεί το κατά πόσο η διαφοροποίηση του περιβάλλοντος διαβίωσης της τσιπούρας Sparus aurata μπορεί να αποτελέσει ένα μέσο εμπλουτισμού του περιβάλλοντος και να βελτιώσει την εντατική εκτροφή της. Έτσι, σχεδιάστηκαν και πραγματοποιήθηκαν πέντε πειράματα.Στο πρώτο πείραμα, διαπιστώθηκε ότι όταν άτομα τσιπούρας (ηλικίας 1+) εκτράφηκαν (84 ημέρες) σε δεξαμενές με Κυανό ή Ερυθροκαφέ υπόστρωμα (ΚΥ και ΕΚΥ αντίστοιχα) βελτιώθηκαν τα χαρακτηριστικά της ανάπτυξής τους (ζων βάρος, ολικό και σταθερό μήκος, ειδικός ρυθμός ανάπτυξης, % αύξηση του ζώντος βάρους) και η αξιοποίηση της τροφής (συντελεστής εκμετάλλευσης της τροφής). Επιπλέον, τα ψάρια του ΚΥ παρουσίασαν καλύτερο συντελεστή ευρωστίας και αυξημένη περιεκτικότητα σε ω-3 πολυακόρεστα λιπαρά οξέα σε δείγμα του ραχιαίου μυϊκού ιστού τους σε σχέση με τα ψάρια των άλλων επεμβάσεων. Ακόμη, παρατηρήθηκε μειωμένη επιθετικότητα στα ψάρια του ΚΥ και ΕΚΥ καθώς επίσης και διαφοροποίηση στα επίπεδα των νευροδιαβιβαστών του εγκέφαλου. Η απασχόληση των ψαριών με τον πυθμένα της δεξαμενής παρατηρήθηκε σε όλες τις επεμβάσεις ανεξάρτητα από την παρουσία του υποστρώματος. Η γενική εικόνα (ανάπτυξη, συμπεριφορά) των ψαριών στις δεξαμενές με Πράσινο υπόστρωμα (ΠΥ) δεν παρουσίασε σημαντικές διαφοροποιήσεις από αυτή των δεξαμενών Χωρίς υπόστρωμα (ΧΥ). Η φυσιολογία των ψαριών όπως εκτιμήθηκε από τις παραμέτρους του πλάσματος του αίματος και του ήπατος που αναλύθηκαν, ήταν παρόμοια μεταξύ των επεμβάσεων.Στο δεύτερο πείραμα, μελετήθηκε κατά πόσο τα ευεργετικά αποτελέσματα του Κυανού και Ερυθροκαφέ υποστρώματος μπορούν να είναι εμφανή ακόμα και όταν η τσιπούρα εκτρέφεται σε διαφορετικές πυκνότητες (98 ημέρες). Σε αυτό το πείραμα χρησιμοποιήθηκαν άτομα τσιπούρας διαφορετικής γενιάς και ηλικίας (0+). Σύμφωνα με τα αποτελέσματα, παρατηρήθηκε ότι τα ψάρια στις δεξαμενές με ΚΥ παρουσίασαν καλύτερη ανάπτυξη (ζων βάρος, ειδικός ρυθμός ανάπτυξης, % αύξηση του ζώντος βάρους), μειωμένη επιθετικότητα, καλύτερη ποιότητα ραχιαίου μυϊκού ιστού ως προς την περιεκτικότητά του σε ω-3 πολυακόρεστα λιπαρά οξέα και μεταβολές στα επίπεδα των νευροδιαβιβαστών του εγκέφαλου. Αντίθετα, τα ψάρια των δεξαμενών με ΕΚΥ αν και παρουσίασαν όμοια αποτελέσματα με αυτά των ψαριών με ΚΥ, δεν παρουσίασαν βελτίωση στην ανάπτυξη. Η φυσιολογία των ψαριών δεν επηρεάστηκε (παράμετροι πλάσματος αίματος και ήπατος, σύσταση σώματος).Στα πρώτα δύο πειράματα, διαπιστώθηκε η θετική επίδραση του χρωματιστού υποστρώματος χαλικιού στην τσιπούρα. Σκοπός του τρίτου πειράματος είναι να διερευνηθούν οι πιθανές επιλογές της τσιπούρας ως προς τα υποστρώματα που είχαν χρησιμοποιηθεί στα προηγούμενα πειράματα. Για το σκοπό αυτό, πραγματοποιήθηκαν δοκιμές προτίμησης σε συνδυασμούς ανά δύο των υποστρωμάτων που χρησιμοποιήθηκαν στα προηγούμενα πειράματα και της επέμβασης ΧΥ. Οι δοκιμές προτίμησης πραγματοποιήθηκαν σε άτομα δύο διαφορετικών ηλικιών (0+ και 2+) ώστε τα αποτελέσματα να συνεκτιμηθούν με αυτά των μακροχρόνιων πειραμάτων. Επίσης, οι δοκιμές έγιναν στα ψάρια ατομικά και σε ομάδες των επτά ατόμων ώστε να εκτιμηθεί η πιθανή εμπλοκή των κοινωνικών σχέσεων στην προτίμησή τους. Στις δοκιμές των τριών υποστρωμάτων με την επέμβαση ΧΥ, παρατηρήθηκε σαφής προτίμηση του ΚΥ ή του ΕΚΥ και απόρριψη του ΠΥ για τα ψάρια και των δύο ηλικιών. Στις δοκιμές μεταξύ των υποστρωμάτων, τα μεγαλύτερα ψάρια προτίμησαν το ΚΥ έναντι του ΕΚΥ ή του ΠΥ, ενώ επέλεξαν το ΕΚΥ μόνο στην περίπτωση που το ΚΥ δε δινόταν ως επιλογή. Αντίθετα, τα ψάρια μικρότερης ηλικίας δεν επέλεξαν μεταξύ του ΚΥ και του ΕΚΥ ή του ΠΥ, ενώ προτίμησαν το ΕΚΥ έναντι του ΠΥ. Επίσης, οι επιλογές των ψαριών δε διέφεραν όταν δοκιμάζονταν ατομικά ή σε ομάδες.Λαμβάνοντας υπόψη τα αποτελέσματα των τριών προηγούμενων πειραμάτων, το επόμενο πείραμα επικεντρώθηκε στο ΚΥ. Σκοπός του τέταρτου πειράματος ήταν να αποσαφηνιστεί η φύση της θετικής επίδρασης του Κυανού υποστρώματος (φυσική παρουσία ή/και χρώμα) και η πιθανή εμπλοκή του φωτεινού περιβάλλοντος στα αποτελέσματα. Για το σκοπό αυτό άτομα τσιπούρας (ηλικίας 0+) εκτράφηκαν σε δεξαμενές με ΚΥ, με τη Φωτογραφία του Κυανού υποστρώματος (ΦΚΥ) ή δεξαμενές ΧΥ (75 ημέρες). Διαπιστώθηκε ότι τα ψάρια του ΚΥ είχαν καλύτερη ανάπτυξη (ζων βάρος, ειδικός ρυθμός ανάπτυξης) και αξιοποίηση της τροφής (συντελεστής εκμετάλλευσης της τροφής), ενώ παρουσίασαν τη χαμηλότερη επιθετικότητα. Οι παράμετροι του αίματος και η δομή του αμφιβληστροειδούς χιτώνα δεν επηρεάστηκαν από τις επεμβάσεις. Επίσης, η φυσιολογία, τα χαρακτηριστικά της ανάπτυξης και η επιθετικότητα των ψαριών στις δεξαμενές με ΦΚΥ δε διέφεραν από των ψαριών του ΧΥ.Τέλος, στο πέμπτο πείραμα μελετήθηκε η πιθανή επίδραση του ΚΥ στην αντίδραση στο stress της τσιπούρας. Το πείραμα σχεδιάστηκε με στόχο τη μελέτη της επίδρασης κατά τη διάρκεια εφαρμογής οξέος stress και κατά την επαναφορά των ψαριών μέσω δεικτών πρωτογενούς και δευτερογενούς αντίδρασης. Άτομα τσιπούρας (ηλικίας 0+) εκτράφηκαν (75 ημέρες) σε δεξαμενές με ή χωρίς ΚΥ και στη συνέχεια υποβλήθηκαν σε stress συνωστισμού για 30, 60 ή 90 λεπτά. Επίσης μελετήθηκε η επαναφορά των ψαριών στις αρχικές συνθήκες ύστερα από 2, 6 ή 24 ώρες. Σύμφωνα με τα αποτελέσματα, τα ψάρια που εκτράφηκαν σε δεξαμενές με ΚΥ παρουσίασαν καλύτερα χαρακτηριστικά ανάπτυξης και μειωμένη επιθετικότητα κατά τη διάρκεια της πειραματικής περιόδου. Επιπλέον, το ΚΥ διαφοροποίησε την αντίδραση στο stress της τσιπούρας.Συμπερασματικά, τα αποτελέσματα της παρούσας Διδακτορικής Διατριβής υποδεικνύουν ότι το Κυανό υπόστρωμα, μέσω της φυσικής του παρουσίας και όχι μόνο του χρώματός του είναι ευεργετικό για την ελεγχόμενη εκτροφή της τσιπούρας Sparus aurata, αφού βελτιώνει τα παραγωγικά της χαρακτηριστικά αλλά και αυτά που σχετίζονται με τη συμπεριφορά της, τροποποιώντας τις κοινωνικές σχέσεις των ψαριών. Η χρήση του Κυανού υποστρώματος σαν ένας αποτελεσματικός τρόπος εμπλουτισμού του περιβάλλοντος που προάγει την ευζωία της τσιπούρας, ενισχύεται περαιτέρω από την προτίμηση του ψαριού για το υπόστρωμα αυτό. Θεωρείται ενθαρρυντικό ότι μια τόσο απλή διαφοροποίηση στο περιβάλλον εκτροφής των ψαριών (όπως το ΚΥ) μπορεί να έχει πολλαπλά οφέλη τόσο για το ψάρι όσο και για τον παραγωγό

Effects of environmental enrichment on growth, aggressive behaviour and brain monoamines of gilthead seabream Sparus aurata reared under different social conditions

The presence of blue or red-brown substrate on the tank bottom has been previously reported as an efficient means of environmental enrichment for gilthead seabream. The present study aimed to investigate whether this enrichment is still beneficial when gilthead seabream is reared under different social conditions (i.e. a lower 4.9kgm-3 and a higher 9.7kgm-3 density). Water exchange was adjusted according to fish biomass to exclude density effects on water quality. In the enriched tanks single-colour glass gravel was used as substrate (blue and red-brown substrate, or BS and RBS respectively), while control tanks had no gravel. Growth, aggressive behaviour and size distribution results indicated that the lower density created a less favourable social environment. In both densities studied, BS enhanced growth, suppressed aggression and reduced brain serotonergic activity. In the condition of intense social interactions (i.e. the lower density) BS also reduced brain dopaminergic activity. These results along with the negative correlations observed between brain monoamines and fish body mass, indicated that substrate and density effects are socially-induced. However, there may be several biotic and/or abiotic factors interfering with substrate effects that should be investigated before the practical use of a substrate in land-based intensive aquaculture. © 2013 Elsevier Inc

Environmental enrichment induces changes in brain monoamine levels in gilthead seabream Sparus aurata

It is generally accepted that environmental enrichment enhances the performance and improves welfare of animals kept in captivity. Similar results have been obtained for fish. It has been previously reported that the presence of Blue or Red-Brown Substrate (BS and RBS respectively) on tank bottom resulted in growth enhancement and suppression of aggressive behavior of gilthead seabream Sparus aurata compared to Green Substrate (GS) and tanks without modifications (Control-C). In an attempt to identify the underlying mechanisms, in the present study the effects of this environmental enrichment on brain monoamine neurotransmitters and fatty acids of gilthead seabream were evaluated. BS and RBS fish had lower serotonergic activity (5-HIAA/5-HT), resulting mainly from lower 5-hydroxyindoleacetic acid (5-HIAA) levels. BS fish also had lower serotonin levels compared to all other treatments. Brain noradrenaline (NA) levels did not show significant differences between substrate treatments and control. Brain dopamine (DA) levels were lowest in BS and RBS fish, higher in GS fish and highest in C fish. No differences were observed for dopamine metabolites or dopaminergic activity. Moreover, brain NA was negatively correlated with body weight in BS fish and positively correlated in RBS and C fish. A positive correlation was also observed for brain DA with body weight in RBS fish. No differences were observed for brain fatty acids. Present results support the hypothesis that the beneficial effects of the presence of BS and RBS are related to altered social interactions and indicate the establishment of a less stressful social organization in enriched-reared fish groups. © 2014 Elsevier Inc

Blue substrate modifies the time course of stress response in gilthead seabream Sparus aurata

Environmental enrichment may attenuate stress response of several vertebrates. In the case of fish, although their stress response is well investigated, the effect of structural complexity as a means of environmental enrichment on stress response is not widely studied. The present study aims to investigate the possible effect of structural enrichment (blue gravel substrate) on gilthead seabream Sparus aurata primary and secondary stress responses during confinement and after recovery. Fish (initial mass 20.3 ± 0.22 g; age 0 +) were reared in tanks with blue substrate (BS) or no-substrate (NS) for 75. days. Fish (triplicated groups) were subjected to 90. min of confinement stress and sampled at 30, 60 and 90. min of confinement, as well as at 2, 6 and 24. h after stress (recovery). Triplicate groups of BS and NS fish were left undisturbed (unstressed fish). During rearing BS fish had better growth performance and less aggressive behavior than NS fish. Plasma cortisol levels and brain neurotransmitters of BS and NS fish were increased during confinement. Cortisol reduction (after stress-induced increase) occurred earlier in NS fish (60 min) than BS fish (90. min), while cortisol levels recovered in 2. h in both treatments. Serotonin metabolite 5-HIAA levels and serotonergic activity (5-HIAA/5-HT) were recovered in 6. h in BS fish, while they remained elevated for NS fish. Dopaminergic system response to confinement showed a transient increase in BS fish (60 min), while no effect was observed in NS fish. Concerning secondary stress response, glucose levels of BS fish decreased after 6. h of recovery while NS fish were not affected. On the other hand, NS fish presented a reduction of triacylglycerides (60 and 90 min) during confinement, while BS fish response was not affected. Osmolality and plasma total protein levels increased at 30. min of confinement and returned to unstressed levels in 24. h in both treatments. Present results indicate that the presence of blue substrate did modify the time course of gilthead seabream stress response to confinement. The overall performance of fish reared with blue substrate suggests that they are in better fitness than fish reared in plain tanks. The efficacy of the blue substrate as environmental enrichment enhancing gilthead seabream welfare is further reinforced and strongly encourages for additional investigations. © 2013 Elsevier B.V

Effect of musical stimuli and white noise on rainbow trout (Oncorhynchus mykiss) growth and physiology in recirculating water conditions

Two musical stimuli transmissions (Mozart and Romanza) as compared with white noise treatment or control, both resulted in significantly higher growth performance in juvenile (6.7 +/- 0.12 g) rainbow trout (Oncorhynchus mykiss) reared for 14 weeks. Carcass chemical composition and fatty acid composition (% of total fatty acids and mg/g carcass wet weight) did not differ among experimental treatments. The same was observed with regard to liver composition. Brain serotonin (5-HT) and its metabolite (5-HIAA) levels were increased in Mozart fish groups compared to all other treatments. However, serotonergic activity (as defined by the 5-HIAA: 5-HT ratio) for the Mozart groups was similar to control groups and was increased in Romanza and white noise fish groups. Brain dopaminergic activity (as defined by the DOPAC: DA ratio, i.e. dopamine metabolite to dopamine levels) was lower in Mozart compared to control fish groups. Differences were also observed as regards total carbohydrase and protease activity in several parts of the digestive tract. In conclusion, the results of the present data indicate that the musical stimuli transmitted were beneficial for the growth performance of rainbow trout. The fact that white noise treatment presented no major differences from control fish groups suggests that this specific stimulus was neither beneficially nor negatively perceived by rainbow trout, while it further supports the hypothesis that it is the musical stimuli per se that make all the difference. (C) 2013 Elsevier B.V. All rights reserved