Melatonin as a Multipotent Component of Fish Feed: Basic Information for Its Potential Application in Aquaculture

Abstract

In vertebrates, melatonin (N-acetyl-5-methoxy-tryptamine, MEL) is synthesized from L-tryptophan (L-Trp), primarily in the pineal gland and additionally in several non-pineal tissues, including enterochromaffin cells of the gastrointestinal tract. The biosynthesis of MEL in the pinealocytes exhibits a daily rhythm with a nocturnal peak in synchronization with the dark phase of an environment. However, the temporal pattern of the gut melatoninergic system in fish is known to be synchronized with one or more non-photic external cue(s), of which most notable include the components of food and feeding time in a daily cycle. Experimental findings on the use of L-Trp (5-fold to −8-fold higher with respect to standard) as a fish food supplement suggest that it has a stimulatory influence on gut MEL synthesis that ultimately leads to elevated levels of plasma MEL. Several studies employing MEL as a fish feed additive report variable responses in relation to the physiological functions of the fish and its doses of application and modes of exposure. Oral administration of MEL (validated dose in general: 200 mg/kg fish food) causes an increase in gut MEL concentrations, food intake capacity, and micronutrient selection ability of fish, as well as enhanced activity of antioxidative enzymes and/or reduced levels of biological stress markers like plasma cortisol and lactate. The application of MEL with the doses of 50 and 250 mg/kg fish food to balanced diet results in precious maturation of gonads, high live sperm rate, and good quality seeds in catfish. A few studies on different fish groups administered with MEL through tank water reveal a significant increase in the fecundity rate, percentage of fertilization, and the number of hatched embryos. MEL injection through intraperitoneal or intramuscular routes also elicits variable responses in fish. Several studies suggest a major protective role of endogenous MEL against gastric ulcer induced by pathogenic bacterial infection. Taken together, MEL seems to be a multipotent physiological candidate involved in the regulation of a variety of body functions ranging from the synchronization of vital activities with environmental variables to the timing of reproduction in a changing system, from the acceleration of body growth to the determination of a pattern of development, and from the reduction of oxidative stress to the protection against microbial infections. Because aquaculture aims at substantially improving the quality and quantity of available aquatic resources employing convenient, consistent, and commercially exploitable measures, we find the reasons to suggest that the use of MEL or its precursor L-Trp as a fish food supplement may open up a new vista of aquaculture and, hence, present this review with an attempt to present the basic information on this area of interest to justify the hypothesis.

Correlation of testicular melatonin and cellular stress in an annual spermatogenic cycle of Clarias batrachus

“…Quality of stored sperm was improved and shown to increase after melatonin administration (0.5µM) in paddle sh (Polyodon spathula) through the inhibition of ROS generation (Gao et al 2019). While there is scarcity of scienti c literature regarding seasonal oxidative status associated with melatonin concentration in testis in any sh, a very few experimental observations suggested its antioxidative role in protecting spermatozoa (Acharyya et al 2021). In addition of ROS, some researchers in mammalian studies suggested that nitrate (a form of NO), a useful marker of nitrosative stress, may stimulate spermatogenesis and the evidence in sh is supported by few studies (Wilson-Leedy and Ingermann 2011, Barman et al 2013).…”

“…The membrane of sh spermatozoa is particularly susceptible to ROS resulting impairment of its motility and fertility (Figueroa et al 2018;Len et al 2019). In order to mitigate cellular stress, a speci c defense system consisting of both enzymatic and non-enzymatic antioxidants aiming to establish a biological equilibrium with the generation of free radicals in testis (Acharyya et al 2021;Félix et al 2023). SOD coverts superoxide anion into hydrogen peroxide which is independently neutralized by heme-containing CAT, and selenium-containing GPx enzyme into water (Hasan et al 2014;Lu et al 2015).…”

Melatonin as an anti-stress signal: effects on an acute stress model and direct actions on interrenal tissue in goldfish

“…Our results suggest that anti-stress effect of MEL can be mediated at different levels of the HPI axis. Bearing in mind the ability of MEL to cross the blood brain barrier ( 17 ), it is expected that this hormone reach neural sites of the HPI axis. Injections of CRH or ACTH increased cortisol in goldfish, which was not reversed by MEL pre-treatment.…”

“…Melatonin (MEL) is a neurohormone mainly synthetized in pineal gland and involved in several physiological activities in vertebrates including fish, playing a role in the adaptive behavior of the animal to the environment (16)(17)(18)(19). As a key signal in the regulation of circadian rhythms, MEL is related to many functions that have in common a rhythmic expression, such as feeding and locomotor activity (16,19).…”

The effects of environmental changes on the endocrine regulation of feeding in fishes

“…Melatonin (the sleep hormone) has been shown to inhibit feeding (e.g. goldfish [89]; zebrafish [90]; European seabass [91]), and affect digestive enzyme activities [92], suggesting that low melatonin levels might be responsible for increases in feeding and feeding efficiency. In pikeperch, Sander lucioperca [93] and goldfish [94], light colour does not affect food intake but blue light increases feed efficiency and growth rates.…”