62 SEPTEMBER 2019 • WORLD AQUACULTURE • WWW.WAS.ORG Implications for Use of Cannabis in Fish Diets These results only pertain to fish being given cannabis daily. There is a growing body of scientific literature suggesting that the effects of cannabis on weight gain and food intake actually depend on whether the drug administration is constant or occasional. Although both acute and chronic cannabis use increase appetite and weight gain in humans (Greenberg et al. 1976), this seems to not be the case with animals administered THC in chronic fashion (Le Foll et al. 2013). As the fish in our experiment were given THC chronically over two months, the observed reduction in weight gain is validated but the possible effects of acute administration are therefore lost to observation. Something similar was observed in Siamese fighting fish Betta splendens, in which THC was used to suppress aggressive behavior but the effect was lost after prolonged administration (Gonzalez et al. 1971). Thus, it is possible that fish experienced a sedative effect in the early stages of the growth trial but then developed tolerance to THC in the diet, precluding any further dietary anti-stress effects. As for the hematology, there were no significant effects of THC on blood or biochemical parameters, although a marginal decrease in WBC, lymphocyte, monocyte and neutrophil counts was noted. There is anecdotal information that marijuana increases the appetite of human consumers (“the munchies”) and results in weight gain. Fish in the present experiment were offered feed at 5 percent body weight daily. If THC offered in the morning feeding was responsible for an increase in metabolic rate, then it is possible if fish were offered feed ad libitum, those treated with cannabis extract might have consumed more and, thus, grown faster. However, even if the fish had grown faster, FCR would have been much higher, resulting in economic loss. Until further research yields different results, we do not believe that there is any benefit to offering cannabis extract to tilapia. Notes Samer Monzer, Dept. of Biology, American University of Beirut, Bliss St., Beirut, Lebanon Imad Patrick Saoud*, PhD, Aquaculture and Aquatic Science, Dept. of Biology, Chair, American University of Beirut, Bliss St., Beirut, Lebanon, * Corresponding author: is08@aub.edu.lb References Adams, I.B. and B.R. Martin. 1996. Cannabis: pharmacology and toxicology in animals and humans. Addiction 91:15851614. Babikian, J., N. Nasser, and I.P. Saoud. 2017. Effects of salinity on standard metabolic rate of juvenile marbled spinefoot (Siganus rivulatus). Aquaculture Research 48:2561-2566. Cabral, G.A. 2001. Marijuana and cannabinoids: effects on infections, immunity, and AIDS. Journal of Cannabis Therapeutics 1:61-85. FAO (Food and Agriculture Organization of the United Nations). 2016. The State of World Fisheries and Aquaculture. Contributing to food security and nutrition for all. Rome, Italy. Gonzalez, S.C., V.K.R. Matsudo and E.A. Carlini. 1971. Effects of marihuana compounds on the fighting behavior of Siamese fighting fish (Betta splendens). Pharmacology 6:186-190. Greenberg, I., J. Kuehnle, J.H. Mendelson and J.G. Bernstein. 1976. Effects of marihuana use on body weight and caloric intake in humans. Psychopharmacology 49:79-84. Hall, W. and N. Solowij. 1998. Adverse effects of cannabis. The Lancet 352:1611-1616. Klein, T.W., H. Friedman and S. Specter. 1998. Marijuana, immunity and infection. Journal of Neuroimmunology 83:102-115. Le Foll, B., J.M. Trigo, K.A. Sharkey and Y. Le Strat. 2013. Cannabis and ∆ 9-tetrahydrocannabinol (THC) for weight loss? Medical hypotheses 80:564-567. Zuardi, A.W. 2006. History of cannabis as a medicine: a review. Revista Brasileira de Psiquiatría 28:153-157. FIGURE 2. Growth in average individual body weight (g) over eight weeks of juvenile O. niloticus offered various diets. 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). FIGURE 3. Mean respiration rates (mg O2 g-1 h-1) of juvenile Nile tilapia O. niloticus offered various diets at 26 C. 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).
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