60 SEPTEMBER 2019 • WORLD AQUACULTURE • WWW.WAS.ORG the most widely and most intensively farmed fish. THC Tilapia Trial We set up a growth trial with prepared diets incorporating cannabis extract to assess the effect of THC on growth, metabolism and stress of tilapia. We also assessed hematological and biochemical parameters – hematocrit, total plasma, lysozyme – to investigate whether the drug improved immune response. The work was performed in the aquaculture research laboratory at the American University of Beirut, Lebanon. Juvenile tilapia where obtained from broodstock maintained in an outdoor system and fed a commercial diet of 40 percent protein and 8 percent lipid (Rangen Inc., Buhl, Idaho, USA). Fish were sorted manually to similar size and transferred to an indoor environmentally controlled RAS, where they were offered commercial feed twice daily to satiation and given two weeks to acclimate. Three isocaloric and isonitrogenous diets were prepared, differing only in the oil source. Diet 1 (control) used soybean oil, diet 2 used industrial hemp oil (no THC) and diet 3 used a 1:1 mix of soybean oil and cannabis oil (with THC) (Table 1). Preliminary trials indicated that the presence of THC and not the concentration affected fish performance, so we opted for the simpler presence/absence of THC in the experiment. Fish were stocked in groups of 11 tilapia juveniles (11 g each) into a controlled indoor system of nine 52-L glass aquaria connected to a settling tank and biofilter (Fig. 1). Each dietary treatment was assigned randomly to three aquaria. Fish were fed for eight weeks, with feed divided into three daily feedings: prepared diet (at 1 percent total average body weight) at 0700 h and commercial feed (at 4 percent BW of the largest fish) divided in two equal rations fed at 1200 and 1800 h. Thus, fish were treated with a dose of cannabis extract every morning and then normal food for the rest of the day. Fish were groupweighed every two weeks after a day of fasting and the feed ration adjusted accordingly. At termination, fish were fasted for 24 h before harvest, anesthetized with a tricaine-S solution, group-weighed by tank, and individual body parameters of all Aquaculture production has grown very rapidly over the last decade and continues to grow at a high rate (FAO 2016). As aquaculture moves away from extensive or semi-intensive pond culture to intensive and super-intensive systems of production in recirculating systems (RAS) and cages, stress and disease incidence resulting from crowding and/or poor water quality increases. Consequently, farming practices that mitigate fish stress would be of great importance to the industry. Cannabis (marijuana, Indian hemp) is a well-known derivative product of some species of annual flowering plants belonging to the Cannabaceae family, indigenous to Central Asia (Adams and Martin 1996, Zuardi 2006). While stems, seeds and oil extracts from the plant have been employed in various ways, including industrial and medicinal purposes, the plant is most well-known for its psychoactive and stress reduction effects. Resin produced by the leaves and flowering tops of C. sativa is a source of terpenes known as cannabinoids, with tetrahydrocannabinol (THC) being the primary psychoactive ingredient responsible for the infamy of the cultivar (Adams and Martin 1996). With the legalization of cannabis in various US states and Canadian provinces, it is only a matter of time before people decide to start giving pot to their animals for whatever reason. Research on the effects of THC in humans and animals provides interesting data that could be of use to aquaculturists. Tetrahydrocannabinol is most known for its sedative effect on certain vertebrates, but there is also evidence for improvement of appetite and increased weight gain in humans and animals (Le Foll et al. 2013). THC might have an immunostimulant effect on vertebrates (Klein et al. 1998, Cabral 2001). These potential effects, coupled with the very low toxicity of THC (Hall and Solowij 1998), provide for a safe feed ingredient/additive that could possibly be used to reduce stress and disease in aquacultured fish. In this article we describe the results of an investigation of the possible effects of THC on Nile tilapia Oreochromis niloticus, one of Does Cannabis Extract Work on Fish: Do Tilapia Get High? Samer Monzer and Imad Saoud FIGURE 1. Research recirculating system with fish.
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