Effects of Gill Fish® on growth and welfare indices of farmed rainbow trout (Oncorhynchus mykiss) during early life stages

In aquaculture, the many chemicals used as therapeutics, prophylactics and growth promoters, can accumulate in fish and spread in the environment through effluent water. Nowadays, the focus of zootechnical productions has shifted towards the search for possible natural alternatives, considered safer for animals and consumers, with lower environmental impact. Herbal products are made of natural compounds, but “natural” is not necessarily synonymous of harmless, thus toxicity needs to be tested for each composition at different doses. Indeed, since herbal products' action is often dose-dependent, negative effects may be prevented by studying the posology according to the species and life stage. In this study, the effects of two different doses (0.05 and 0.1 mL/L) of a natural-based complementary feed, Gill Fish®, were assessed on the early stages of life of farmed rainbow trout (Oncorhynchus mykiss). The product was added daily to tanks containing rainbow trout eggs during the pre-hatching period, from 30 to 36 days post fertilization. Embryos mortality (evaluated three times during the six days of treatment; t0-t2) and zootechnical indices such as biomass, weight, length and number of alevins (all evaluated 3 and 4 weeks after the end of treatment; t3-t4), were analysed to assess both direct and indirect toxicity. Furthermore, whole body cortisol (from embryos and alevins; t0-t4) was measured to highlight potential stressful effects of the treatment. For each parameter, time was a statistically significative factor, while no differences were noticed between the three groups within the same time point. These results demonstrate that Gill Fish® had no harmful nor stressful effects, both immediately and short term; this herb-based product could therefore be a good candidate for future studies with different doses and/or longer administration, to evaluate its possible beneficial effects as an alternative to chemicals in aquaculture.