Environmental blue light prevents stress in the fish Nile tilapia

Abstract

The present study aimed to test the effects of blue, green or white light on the stress response of the Nile tilapia, Oreochromis niloticus (L.). Each color was tested on two groups of isolated adult Nile tilapia (8 replicates each): one being subjected to confinement stress, and the other not (control). A different environmental color was imposed on each compartment by covering the light source with cellophane of the respective color (green or blue; no cellophane was used for white light). The intensity of green, white and blue lights was 250, 590 and 250 lux, respectively. Basal plasma cortisol levels were determined for each fish prior to the experimental procedures. The fish were confined by being displaced toward one side of the aquarium using an opaque partition for 1 h both in the morning and the afternoon of the two consecutive days of the test. At the end of this 48-h period, plasma cortisol levels were measured again. Basal cortisol levels (ng/ml) were similar for each group (ANOVA, F (2;42) = 0.77, P = 0.47). Thus, plasma cortisol levels were analyzed in terms of variation from their respective basal level. After confinement, plasma cortisol levels were not increased in fish submitted to a blue light environment. Thus, blue light prevents the confinement-induced cortisol response, an effect not necessarily related to light intensity.

Stress responses of the fish Nile tilapia subjected to electroshock and social stressors

“…Mean pre-stressor cortisol levels ranged from 41.57 to 65.67 ng/mL (Figure 2), in agreement with other studies. For instance, the baseline described for O. niloticus ranged from ~5 to 60 ng/mL (10,11,17,23,24), and for the related Cichlid, O. mossambicus, it ranged from ~20 to 60 ng/mL (33), and from about 10 to 60 for other fish species (3)(4)(5)(6)19,34).…”

“…Such modifying factors may be either a non-stressor or inherent to the stressor trait. For instance, sexual maturity (4), environmental color (17,18), heritability (7), age (3), and feeding state (8) are non-stressful conditions that modulate the stress response. On the other hand, intensity and duration are stressor characteristics that affect stress (1,2).…”

“…We chose the fish species Nile tilapia, Oreochromis niloticus, because it is an important fish model for studying the stress response (9)(10)(11)(12)(13)17,21,23,24) and has evident agonistic behavior (11,12,22,25,26), both aspects related to the proposed hypothesis.…”

Visual communication stimulates reproduction in Nile tilapia, Oreochromis niloticus (L.)

“…Blue is known to reduce stress (24) and improve reproduction (16) in Nile tilapia. Water temperature was maintained at 27 ± 1°C by individual thermostats and the photoperiod was 12-h light/dark cycles, starting at 7:00 am.…”

Atividade da catalase e da lactato desidrogenase em tilápias submetidas a estresse de confinamento: efeito da cor do ambiente

“…Esta cor aumenta a agressividade ou estresse em peixes territoriais como O. niloticus (FANTA, 1995;MERIGHE et al, 2004), reduz o crescimento em Perca flavescens (HEAD & MALISON, 2000) e evita o aumento dos níveis plasmáticos de cortisol em resposta ao estresse em O. niloticus VOLPATO & BARRETO, 2001), Rhamdia quelen (BARCELLOS et al, 2006), Pagrus pagrus (VAN DER SALM et al, 2004) e Onchorhynchus mykiss (KARAKATSOULI et al 2008). O espectro de luz azul inibe a mobilização de lipídeos hepáticos induzida pelo estresse em O. mykiss (KARAKATSOULI et al, 2008), aumenta a eficiência alimentar em larvas de Melanogrammus aeglefinus (DOWNING & LITVAK, 2001) e favorece o crescimento em Perccottus glenii e Poecilia reticulata, efeito não observado em Carassius carassius (RUCHIN, 2004).…”