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

Abstract

Black Soldier Fly (BSF) meal is considered as an alternative, emerging and sustainable ingredient for aquafeed production. However, results on fish physiological responses are still fragmentary and often controversial, while no studies are available on fish behavior in response to these new diets. The present work represents the first comprehensive multidisciplinary study aimed to investigate zebrafish physiological and behavioural responses to BSF-based diets. Five experimental diets characterized by increasing inclusion levels (0, 25, 50, 75 and 100% respect to fish meal) of full fat BSF prepupae meal were tested during a 2-months feeding trial. Prepupae were cultured on coffee silverskin growth substrate enriched with a 10% Schizochytrium sp. to improve insects' fatty acids profile. The responses of zebrafish were assayed through biometric, histological, gas chromatographic, microbiological, spectroscopic, molecular and behavioural analyses. Results evidenced that BSF-based diets affected fish fatty acid composition, while behavioural tests did not show differences among groups. Specifically, a 50% BSF inclusion level diet represented the best compromise between ingredient sustainability and proper fish growth and welfare. Fish fed with higher BSF inclusions (75 and 100%) showed hepatic steatosis, microbiota modification, higher lipid content, fatty acid modification and higher expression of immune response markers. The promotion of high-quality fish production as well as fish welfare are the main aquaculture goals, both strictly related to an adequate fish nutrition 1. The use of fish meal (FM) and fish oil (FO) in aquafeed formulation is no more feasible because of important environmental and economic issues 2. Over the last decades, several alternative ingredients (plant origin proteins, microalgae and processed animal proteins) to FM and FO have been tested 3. However, each of these ingredients showed some disadvantages in its application in aquafeed formulation including unbalanced amino acid profile, poor protein digestibility, presence of anti-nutritional factors and high production costs 3,4. Insects are now considered as an alternative and sustainable ingredient for feed production 5. In particular, the Black Soldier Fly (Hermetia illucens; BSF) larvae are one of the most promising candidates because of their proper protein content and the amino acid composition similar to that of FM 6,7. In addition, BSF have low environmental requirements, a high feed conversion efficiency and they can growth on organic by-products, promoting sustainability and the circular economy concept in the aquaculture sector 8,9. Several studies tested different BSF inclusion levels in aquafeed formulation but results on fish physiological responses are still controversial, while behavioural effects on fish are completely missing 10-13. The use of BSF in aquafeed has been shown, at certain inclusion levels,

Physiological responses of Siberian sturgeon (Acipenser baerii) juveniles fed on full-fat insect-based diet in an aquaponic system

“…Previous studies, based on a limited number of laboratory approaches, highlighted that a defatted BSF prepupae meal dietary inclusion level higher than 25% impaired fish growth and welfare [31][32][33] . Based on these results and previous studies which demonstrated the possibility to use higher full-fat dietary BSF meal inclusion levels 23,38 after an enrichment procedure of the insect biomass 39 , the present study aimed to: (i) test, for the first time, a 50% enriched full-fat BSF prepupae meal inclusion level in a practical diet for juvenile www.nature.com/scientificreports/ sturgeons in an aquaponic system; (ii) apply a set of laboratory techniques to examine comprehensively the physiological responses of the fish. The results showed that the inclusion of a 50% enriched full-fat BSF prepupae meal negatively affects fish growth and survival.…”

“…However, BSF meal fatty acid profile has also some disadvantages, such as a high content of saturated fatty acids (SFA) and an extremely low content in polyunsaturated (PUFA) ones 20 . PUFA are particularly important for fish since deficiencies in these compounds may cause a general deterioration of fish health, poor growth, low feed efficiency and often high mortality 21 – 23 . Previous studies demonstrated that a proper PUFA dietary content is essential to sustain both larval and adult Siberian sturgeon growth and welfare 24 , 25 ; these compounds play a pivotal role in sturgeon’s fillet and caviar quality 26 .…”

“…This topic, however, has scarcely been investigated in sturgeon aquaculture and most of the results are limited to zootechnical analyses 31 – 33 . Nowadays, several laboratory approaches (histology, molecular biology, gas chromatography and infra-red spectroscopy) are available to evaluate fish welfare and quality and represent valid tools to assess the inclusion of new ingredients, like insect meal, in aquafeed production 23 , 34 – 36 . In addition, the use of full-fat BSF meal is preferable to the highly defatted in order to reduce manufacturing costs 37 , 38 .…”

Consumer Acceptance of Meat from Animals Reared on Insect Meal as Feed

“…Moreover, when using defatted insects, they are rich in protein and the insect oil could be used as a good source of omega-3 FAs. The oil composition depends on the species and the feed of the insects [14,15]. In recent years, several papers have been published that show that fishmeal and soy can be partially or completely replaced by insect meal in poultry [16][17][18], in pigs [19], and in fish [20,21].…”

Possible Dietary Effects of Insect-Based Diets across Zebrafish (Danio rerio) Generations: A Multidisciplinary Study on the Larval Phase

“…In particular, the Black Soldier Fly ( Hermetia illucens ; BSF) is able, during its larval development, to grow on organic by-products, converting them into valuable biomass with a nutritional composition dependent on the quantity and the quality of feed offered [ 6 , 7 , 8 ]. Due to its promising protein content and essential amino acid pattern, the use of different BSF dietary inclusion levels has been widely investigated in several farmed fish species, including rainbow trout ( Oncorhynchus mykiss ) [ 9 , 10 ], Atlantic Salmon ( Salmo salar ) [ 11 , 12 ] and Siberian sturgeon ( Acipenser baerii ) [ 13 , 14 ], as well as in experimental models like zebrafish ( Danio rerio ) [ 8 , 15 , 16 ]. In addition, as recently reviewed by Zarantoniello and collaborators [ 17 ], different diets in terms of BSF dietary inclusions, developmental stage (larvae or prepupae) and lipid content (full-fat, partially or totally defatted) have been tested in recent years on several fish species.…”