Postprandial kinetics of digestive function in rainbow trout (Oncorhynchus mykiss ): genes expression, enzymatic activity and blood biochemistry as a practical tool for nutritional studies

Postprandial kinetics of genes expression of gastric (chitinase, pepsinogen) and intestinal (alkaline phosphatase, maltase) digestive enzymes and nutrient transporters (peptide transporter 1, sodium-glucose transporter 1), Brush Border Membrane (BBM) enzymes activity (alkaline phosphatase, leucine aminopeptidase, maltase, saccharase) and blood biochemistry (triglycerides, cholesterol, protein, albumin, glucose, amino acids) through NMR spectroscopy, were investigated in rainbow trout (Oncorhynchus mykiss) fed a commercial aquafeed. For this purpose, fish were starved 72 h and digestive tract and blood were sampled before the meal and at 1.5, 3, 6, 9, 12, and 24 h after feeding (T0, T1.5, T3, T6, T9, T12 and T24). The postprandial kinetic showed that the expression of the genes involved in digestion and nutrient transport, the activity of BBM enzymes, and the presence of metabolites in blood were stimulated in different ways by the presence of feed in the digestive tract. The expression of most genes peaked 3 h after meal except gastric pepsinogen and maltase in distal intestine that peaked at T9 and T12, respectively. The activity of BBM enzymes were stimulated differently based on the intestine tract. The plasma proteins level increased from T1.5 until T9, while the other blood parameters unvariated during the postprandial period. This study supplied useful information about the physiological effects a single meal as a potential tool for planning nutritional studies involving the digestive functions

Chemical composition and apparent digestibility of a panel of dried microalgae and cyanobacteria biomasses in rainbow trout (Oncorhynchus mykiss)

Despite a growing interest in microalgae and cyanobacteria as potential sources of nutrients in aquafeeds, little information is presently available on their nutritive value for carnivorous fish species. The aim of this study was to evaluate chemical composition and nutrient digestibility of a panel of microalgae and cyanobacteria dried biomasses (MACB), using rainbow trout (Oncorhynchus mykiss W.) as a fish model. Nine test diets were obtained by mixing 80 parts of a reference diet, added with 20 g/kg of acid insoluble ash as an indigestible marker, to 20 parts of each of the following dried whole-cell biomass: Arthrospira platensis, Nostoc sphaeroides, two strains of Chlorella sorokiniana, Nannochloropsis oceanica, Tisochrysis lutea, Phaeodactylum tricornutum, Porphyridium purpureum and Tetraselmis suecica. The digestibility measurements were conducted with rainbow trout (52.4 \ub1 1.5 g) kept in six tank units each including three 60-L vessels singularly stocked with 12 fish and fitted with a settling column for faecal recovery. Per each diet, faeces were collected over three independent 10-day periods. Apparent digestibility coefficients (ADCs) of dry matter, crude protein (CP), organic matter and gross energy (GE) of single MACB were calculated by difference relative to those of the reference diet. The MACBs had heterogeneous chemical composition (CP, from 20 to 69%; Lipid, 5\u201327%; GE, 12.5-\u201322.6 MJ/kg dry matter basis) reflecting their overall biodiversity. Most of them can be considered as virtually good sources of minerals and trace elements and exhibit an essential amino acid profile comparable or even better than that of soybean meal commonly used in fish feeds with P. purpureum showing the best protein profile. The digestibility results obtained with rainbow trout allowed ranking the MACBs into two major groups. A first one, including C. sorokiniana, N. oceanica and T. suecica, resulted in markedly lower (P < 0.05) crude protein and energy ADC (64\u201373%; 51\u201359%, respectively) compared to a second group including P. purpureum, T. lutea and cyanobacteria (CP-ADC, 83\u201388%; GE-ADC, 74\u201390%) while P. tricornutum resulted in intermediate values. Overall, the present study confirms the consistently reported role of cell-wall structure/composition in affecting accessibility of nutrients to digestive enzyme. Based on the overall outcomes, only T. lutea and cyanobacteria actually meet the requirements for being used as protein sources in aquafeeds provided their mass production becomes more feasible and costeffective, hence attractive for the feed-mill industry in the near future

Growth and Welfare Status of Giant Freshwater Prawn (Macrobrachium rosenbergii) Post-Larvae Reared in Aquaponic Systems and Fed Diets including Enriched Black Soldier Fly (Hermetia illucens) Prepupae Meal

Due to the limited application of insect meal in giant freshwater prawn (Macrobrachium rosenbergii) culture, the present study aimed to (i) produce spirulina-enriched full-fat black soldier fly (Hermetia illucens) prepupae meal (HM) and (ii) test, for the first time, two experimental diets characterized by 3% or 20% of fish meal and fish oil replacement with full-fat HM (HM3 and HM20, respectively) on M. rosenbergii post-larvae during a 60-day feeding trial conducted in aquaponic systems. The experimental diets did not negatively affect survival rates or growth. The use of spirulina-enriched HM resulted in a progressive increase in α-tocopherol and carotenoids in HM3 and HM20 diets that possibly played a crucial role in preserving prawn muscle-quality traits. The massive presence of lipid droplets in R cells in all the experimental groups reflected a proper nutrient provision and evidenced the necessity to store energy for molting. The increased number of B cells in the HM3 and HM20 groups could be related to the different compositions of the lipid fraction among the experimental diets instead of a nutrient absorption impairment caused by chitin. Finally, the expression of the immune response and stress markers confirmed that the experimental diets did not affect the welfare status of M. rosenbergii post-larvae

Optimization of an OLED-based immunosensor for the detection of tetrodotoxin in mussels

Alien species have colonized new aquatic ecosystems due to multifactorial effects, among which climate change or the increasing marine traffic, can be mentioned. The occurrence of contamination due to tetrodotoxin (TTX) is now observed in the Mediterranean Sea and in bivalves, whereas TTX was classically contaminating pufferfish in the Pacific Ocean. In this paper, we present the optimization of an Organic Light Emitting Diode (OLED) based immunosensor to detect tetrodotoxin in spiked samples of mussels. An ELISA test was preliminary optimized to set the concentrations of all biological elements required to develop the OLED-immunoaffinity-based biosensor and to mutually validate the two detection systems presently optimized. The threshold concentration of 44 ng g−1 set by EFSA for TTX in seafood products was used to distinguish the negative mussel samples from the positive ones. A streamlined extraction protocol was adopted after its optimization to fulfil the need of the assay (European Food Safety Authority, 2017)

Effects of supplementing a plant protein-rich diet with insect, crayfish or microalgae meals on gilthead sea bream (Sparus aurata) and European seabass (Dicentrarchus labrax) growth, physiological status and gut health

This study was aimed at evaluating growth response, gut health and physiological status of seabream (GSB) and European seabass (ES) juveniles fed diets totally deprived of fish meal and supplemented with alternative ingredients. Fish were fed four isoproteic (45%) and isolipidic (20%) diets in which meals from black soldier fly (Hermetia illucens, H) prepupae, whole red swamp crayfish (Procambarus clarkii, RC) or a microalgae blend (Tisochrysis lutea and Tetraselmis suecica, MA) were used as supplements to replace 10% protein of a fish meal-free, plant protein-based diet high in soybean meal (CV). Each diet was fed to triplicate fish groups kept in a RAS (Temperature 23.5 °C, Salinity 29 ppt) over 12 (GSB) and 18 (ES) weeks. In both fish species, MA diet resulted in the worst specific growth rate (SGR), feed conversion ratio (FCR) and protein efficiency ratio (PER) compared to CV. Diet H significantly improved the SGR only in GSB without affecting FCR. The dry matter apparent digestibility coefficient (ADC) was highest in the H diet (approximately 76%) and lowest in MA (around 73%), while an intermediate value was recorded for the RC diet, in both fish species. Slightly inflamed intestine and altered mucosa morphology were observed in both fish species fed on CV diet, highlighting a higher susceptibility of GSB to this diet. On the contrary, diets H, RC and MA led to a modulation of inflammatory gene expression in the distal intestine from the two fish species. However, while H and RC diets lead to a more evident intestine status improvement in GSB, in ES this result was evident even in response to MA diet administration. The MA diet induced a lowering of nutritional status compared to CV in both GSB and ES. Overall the results have shown that 10% protein from H and RC in a plant protein-based diet, tends to improve fish growth and gut health in both fish species. In ES also the diet including microalgae turned in a beneficial effect on fish gut health, compared to CV one, although it needs further refinement to reduce the adverse impact on growth and physiological status. Our findings suggest the potential use of insect and crayfish meals as functional ingredients in fish meal-free diets for GSB and ES, while further studies are needed to refine the use of microalgae as functional feed supplements in diets for sub-adult gilthead seabream and European seabass