Investigating fishmeal replacement with insect meal in "aquafeed" using zebrafish (Danio rerio) as animal model

The world population is continuously growing and it is expected to reach 9 billions of people by 2050. In this context, to secure food for everyone it is necessary to double the world food production and in the last decades, Aquaculture is already significantly increasing its production worldwide. Unfortunately, fish nutrition strictly relies on the use of fishmeal (FM) as source of protein and the intensive catch of herrings, anchovies and sardines have strongly reduced the consistence of the fish wild stocks; hence, the production of supplementary quantities of FM is considered not realistic and, in particular, not “sustainable”. As a consequence, the market price of FM have been dramatically increasing in the last decades and the feed industry and research Institutions are now strongly engaged in seeking valid alternative to this important protein source (FAO, 2014). Currently, the majority of FM replacement have been done with vegetal ingredients such as soybean, soybean extracts, corn gluten and other grains, all of them somehow characterized by an unbalanced amino acid profiles, presence of anti-nutritional factors and limited digestibility rates. In this context, thanks to its low “carbon footprint” and production sustainable, insect meal (IM) may represent a valid alternative to FM (FAO, 2013). Hence, the aim of this study was to evaluate the effects of replacing FM with IM, in fish feed. The IM used was made by Hermetia illucens larvae (Insect protein meal®, Protix©, Dongen - NL); since several Authors refer that Zebrafish (Danio rerio) can be considered a suitable animal model for aquaculture nutrition research (Dahm e Geisler, 2006; Ulloa, 2011; Ulloa 2014), it was used to carry out the present study at the zebrafish facility of the Department of Veterinary Science of the University of Pisa. In particular, 320 juveniles (Wild-Type; AB Line; body weight 85±25 mg (m±ds); 60 days old) were randomly divided into four groups and four replicates, and fed 4 diets (iso-energetic and iso-proteic) each differing for the IM/FM replacing rate, as follow: Control, no IM and 20% FM (0% FM replacement); HI25%, 5 % IM and 15% FM (25% FM replacement); HI50% 10 % IM and 10% FM 50% FM replacement); HI 100%, 20% IM, no FM (100% FM replacement). The feed, extruded, was produced by Sparos© (Olhão - P), spin-off company of the University of Algarve, and fed four time per day for a 49 days total period. The diet’s effects on fish were investigated through the growth performances, mortality rate, feed consumption and feed conversion rate; also, at the end of the experimental period, the fish intestine was sampled for performing histological analysis (villi length and diameter, globlet cells counts). All the performances and parameters observed were consistent to those normally observed on other freshwater and marine fish, this meaning that zebrafish can be a suitable animal model for studies on fish growth performances and nutrition in aquaculture. In fact, at the end of the trial, zebrafish have almost tripled their body weight. For all the considered parameters, the groups fed IM did not show differences (p>0.05) within experimental groups, as well as in comparison to the control group. The final mean body weights reached by each group were: control group 229 mg; 0% 237 mg; HI50 242 mg; HI100 229 mg; feed conversion ratios were: control group 2.11; HI25 2.05; HI50 1.94; HI100 2.08. Only significant differences (p<0.05) were observed between males and females fish, hence independently from the considered treatments. In conclusion, results suggest that when insect meal from Hermetia illucens is included up to 20% in Zebrafish feed, it is a valid alternative for replacing fishmeal in Zebrafish and, verisimilarly, in other fish aquacultured fish species.