A six-months study on Black Soldier Fly (Hermetia illucens) based diets in zebrafish

Abstract

Intensive fish farming relies on the use of feeds based on fish meal and oil as optimal ingredients; however, further development of the aquaculture sector needs new, nutritious and sustainable ingredients. According to the concept of circular economy, insects represent good candidates as aquafeed ingredients since they can be cultured through environmental-friendly, cost-effective farming processes, on by-products/wastes, and many studies have recently been published about their inclusion in fish feed. However, information about the physiological effects of insect-based diets over the whole life cycle of fish is presently missing. At this regard, the present study investigated, for the first time, the effects of Black Soldier Fly based diets (25 and 50% fish meal substitution) administration for a six months period in zebrafish ( Danio rerio ), from larvae to adults. A multidisciplinary approach, including biometric, biochemical, histological, spectroscopic and molecular analyses was applied. Aside a general reduction in fish growth and lipid steatosis, six-months feeding on Black Soldier Fly based diets did not show major negative effects on zebrafish. Gut histological analysis on intestine samples did not show signs of inflammation and both stress markers and immune response markers did not show significant differences among the experimental groups.

Zebrafish (Danio rerio) physiological and behavioural responses to insect-based diets: a multidisciplinary approach

“…In accord to previous studies 11,12,34 , the present results evidenced that fish growth was positively affected by the increasing inclusion levels of enriched BSF prepupae meal in the diets. Surprisingly, and differently from previous studies 21,29,33 , in the present research, biometric results were not fully supported by the molecular ones that evidenced a decreasing igf1 and igf2a gene expression and an opposite trend for mstnb in the liver, followed by the increasing dietary BSF meal inclusion levels. It should be pointed out that the principal environmental regulator of the growth hormone (GH)-IGF axis is the organisms' nutritional status 35 .…”

“…This condition agrees with the higher intestine ghrl and cnr1 gene expression observed in Hi75 and Hi100 zebrafish groups since the regulation of orexigenic signals (ghrelin in particular) is associated with different factors including GH and Igf1 concentrations 39 . Furthermore, as reported by previous studies on zebrafish, fish fed BSF-based diets showed better growth performances with respect to a control diet during the larval phase 19,33 , while this was not evident over a six-months feeding trial 21 . In the present study, a reduction in the SGR% difference among the experimental groups was evident (especially if compared to the larval stage 19 ) and this can be related to the well-known different growth rates of larval, juvenile and adult fish 40 .…”

“…In particular, Truzzi et al (2020) 9 demonstrated that the addition of a 10% (w/w) of Schizochytrium sp. to the growth substrate was an efficient method to enrich BSF final biomass in terms of PUFAs and to increase, with respect to previous studies on zebrafish, the BSF meal inclusion level in the fish diets without affecting fish welfare 21,29,33 . However, the potential of these enriched BSF prepupae as alternative feed ingredient for fish was evaluated only during the fish larval stage 19 .…”

“…significantly increased insects' PUFAs content. With respect to previous studies carried out on zebrafish 21,29 , this enriching procedure allows to include up to 50% of BSF meal in the fish diet without impairing fish physiology, and hence represents a remarkable example of sustainable circular economy. Zebrafish represents an ideal organism to better understand fish physiological responses to new ingredients 30 and an emerging useful model organism for neuroscience/behavioural research 31 .…”

“…Most insect species, including BSF, are rich in saturated fatty acids (SFA) and contain negligible amounts of polyunsaturated (PUFA) ones 20 . A high dietary SFA content, coupled with a high n6/n3 ratio, has been shown to play a key role in fish hepatic steatosis development 13,21 . Furthermore, insect meal may alter the biochemical characteristics of fish fillet, especially regarding the fatty acid composition, even in absence of major alterations of its sensory properties 12,22 .…”