Effects of different feeding frequencies on growth, feed utilisation, digestive enzyme activities and plasma biochemistry of gilthead sea bream (Sparus aurata) fed with different fishmeal and fish oil dietary levels

In the context of Mediterranean aquaculture little attention has been paid to the manipulation of feeding frequency at the on-growing phase. The effects of different feeding frequencies: one meal per day, two meals per day, three meals per day on growth, digestive enzyme activity, feed digestibility and plasma biochemistry were studied in gilthead sea bream (Sparus aurata, L. 1758) fed with high and low fishmeal and fish oil levels. Isonitrogenous and isolipidic extruded diets were fed to triplicate fish groups by a fixed ration over 109 days. No significant effects of feeding frequency on overall performance, feed efficiency and feed digestibility during the on-growing of gilthead sea bream fed high or low fishmeal and fish oil dietary level were observed. Pepsin activity showed an apparent decrease in fish receiving more than one meal a day which was not compensated by an increased production of alkaline proteases particularly in fish fed on low FM. Although there were no effects on growth and feed utilisation at increasing feeding frequency, trypsin decreased significantly with an increasing number of meals only under low FMFO diet. Thus, it seemed that consecutive meals could have amplified the potential trypsin inhibitor effect of the vegetable meal-based diet adopted. Results of the plasma parameters related to nutritional and physiological conditions were not affected by feeding frequency. The higher level of plasma creatinine detected in fish fed a single daily meal with high FMFO level seems to be within physiological values in relation to the higher protein efficiency observed with this diet. According to the results, gilthead sea bream seems able to maximise feed utilisation regardless of the number of meals, and this could be a useful indicator for planning feeding activity at farm level to optimise growth of fish and costs of feeding procedures

Interaction Between Dietary Lipid Level and Seasonal Temperature Changes in Gilthead Sea Bream Sparus aurata: Effects on Growth, Fat Deposition, Plasma Biochemistry, Digestive Enzyme Activity, and Gut Bacterial Community

A 121-day feeding trial was undertaken to test the effects of two dietary lipid levels (16 and 21% L16, L21) in triplicated gilthead sea bream groups (initial weight: 67.5 g) reared at two different water temperatures (high, H 23°C and low, L 17°C) in the same recirculation system but exposed to a switch in temperature after 58 days. Fish kept at H were transferred to L (HL transition, autumn shift), and the fish kept at L were exposed to H (LH transition, summer shift), while continuing to receive the same diet to apparent satiation in each group. At the end of the trial, no significant diet effect on specific growth rate (SGR), feed intake (FI), and feed conversion rate (FCR) were detected in fish exposed to HL transition compared with those exposed to LH transition, while gross lipid efficiency (GLE) and lipid efficiency ratio (LER) were higher in L16. After temperature changes, L16 displayed higher SGR, FI, GLE, and LER, while mesenteric fat index was reduced. After temperature changes, the combined effects of low lipid diet and low temperature conditions resulted in higher pepsin activity, while trypsin, chymotrypsin, and lipase activities were generally higher at high lipid content. The combined effect of diet and temperature did not alter the metabolic plasma profile, except for the observed final higher aspartate aminotransferase (AST) and alkaline phosphatase (ALP) values when combining high dietary lipid (L21) and temperature changes. Different diets showed a significantly different gut microbiome layout, only at high temperature with L16 diet resulting in a higher load of Lactobacillus. On the contrary, no dietary impact on ecosystem diversity was observed, independently from the temperature. In addition, L16 diet in the HL transition favored an increase in Weissella and Bradyrhizobium genera in the gut microbiome, while in the final condition of LH transition, L21 diet favored a significant increase in Streptococcus and Bacillus. According to the results, the utilization of 16% dietary lipid levels in gilthead sea bream should be preferred during seasonal temperature changes in order to optimize feed utilization and gut health

GH/IGF AXIS GENE EXPRESSION PROFILE IN DEVELOPING ATLANTIC BLUEFIN TUNA (Thunnus thynnus)

Atlantic bluefin tuna (ABFT), Thunnus thynnus (Linnaeus, 1758), is a large migratory oceanic top predator, considered as an important worldwide fishery source and a key species in pelagic ecosystems. Survival during the early life stages is crucial for future recruitment success, with larval growth being a determining process. Fish growth and development are mainly controlled by the GH/IGF axis, being involved in skeletal and soft tissue growth, as well as in immune function, appetite control, behavior (including foraging, aggression, and predator avoidance). To characterize the ontogenetic development profile of the GH/IGF axis at the level of gene expression, an ABFT larval rearing experiment (under controlled feeding conditions) was performed in the aquaculture facilities of the Spanish Institute of Oceanography (IEO), in Mazarrón during June 2019. Eggs and larvae from 3 replicates were collected regularly every 2-3 days from 0 until 30 days post-hatching (dph). In a total of 14 sampling points (n = 6-12 larvae) along the ontogeny, growth hormone (gh) and two forms of insulin growth factor (igf1 and igf2) were analyzed by real-time RT-PCR. A sigmoidal gh expression profile was observed, with higher values at 5 and 23 (maximum) dph, and lower values at 0 (minimum), 12 and 30 dph. Nevertheless, igf1 and igf2 showed a gradual increase from early days, also with lower values at 0 and 12 dph, but with maximum levels at 30 dph. Results are discussed considering growing rates and transition from larvae to juvenile, underlining the importance of gh/ igf axis during the ABFT early development and growth

gh/igf axis gene expression profile in developing atlantic bluefin tuna (Thunnus thynnus).

Atlantic bluefin tuna (ABFT), Thunnus thynnus (Linnaeus, 1758), is a large migratory oceanic top predator, considered as an important worldwide fishery source and a key species in pelagic ecosystems. Survival during the early life stages is crucial for future recruitment success, with larval growth being a determining process. Fish growth and development are mainly controlled by the GH/IGF axis, being involved in skeletal and soft tissue growth, as well as in immune function, appetite control, behavior (including foraging, aggression, and predator avoidance). To characterize the ontogenetic development profile of the GH/IGF axis at the level of gene expression, an ABFT larval rearing experiment (under controlled feeding conditions) was performed in the aquaculture facilities of the Spanish Institute of Oceanography (IEO), in Mazarrón during June 2019. Eggs and larvae from 3 replicates were collected regularly every 2-3 days from 0 until 30 days post-hatching (dph). In a total of 14 sampling points (n = 6-12 larvae) along the ontogeny, growth hormone (gh) and two forms of insulin growth factor (igf1 and igf2) were analyzed by real-time RT-PCR. A sigmoidal gh expression profile was observed, with higher values at 5 and 23 (maximum) dph, and lower values at 0 (minimum), 12 and 30 dph. Nevertheless, igf1 and igf2 showed a gradual increase from early days, also with lower values at 0 and 12 dph, but with maximum levels at 30 dph. Results are discussed considering growing rates and transition from larvae to juvenile, underlining the importance of gh/ igf axis during the ABFT early development and growth

Ontogeny and diurnal patterns of molecular gene expression and activity of digestive enzymes in developing greater amberjack

The greater amberjack, Seriola dumerili, is a fast-growing pelagic teleost with great interest for the diversification of farmed marine fish species in the Mediterranean region. Aiming to advance the optimization of feeding during the early stage of this species, this study examines the ontogeny of digestive function using molecular and biochemical approaches. Gene expression of digestive enzyme precursors and the enzymatic activity have been determined during the first 51 days post hatching (dph) and during the diurnal period of 19 dph larvae reared in semi-intensive conditions. The expression of pancreatic proteases precursors (try3, ctra and ctrb1) increased from first-feeding, while gastric chitinase (chia1), gastric protease (pga3) and proton pump (atp4a2) after 10 dph. The expression of pancreatic lipases (cel1, cel2 and cel3) peaked between 6 and 10 dph, phospholipase A2 (pla2g1b) rose only after 25 dph, while a-amylase (amy2a) increased mainly from 20 dph. The trypsin activity was more evident from first-feeding to 25 dph and chymotrypsin activity from this day onwards. Acidic chitinase and pepsin activity appeared, respectively, at 16 and 30. The activity of 7C-like lipase was evident from first-feeding but as 4C-like lipase significantly increased from 15 dph, while amylase peaked from 6 to 22 dph. Aminopeptidase and alkaline phosphatase activities started at 20 dph indicating the functional maturation of brush border of the enterocytes. The daily pattern analysis showed a food anticipatory strategy in the expression of proteases related genes. Lipases activity was more evident during the morning hours, followed by amylase, and by alkaline proteases in the afternoon. Results, also, suggested an alternation in the activity of chymotrypsin and trypsin. These ontogenetic patterns are concordant with a carnivorous marine teleost.Spanish Ministry of Science, Innovation and Universities (MCIU) [RTI208-096134-B-I00]; State Research Agency (AEI); European Regional Development Fund (FEDER/ERDF); Erasmus fellowship (Erasmus+); FCT (Portugal)Portuguese Foundation for Science and TechnologyEuropean Commission [UIDB/04326/2020

Characterization of GH/IGF axis gene expression during Atlantic bluefin tuna (Thunnus thynnus) larval development in NW Mediterranean waters

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Interaction between dietary composition and seasonal temperature changes in gilthead sea bream Sparus aurata: effects on growth, fat deposition, plasma biochemistry, digestive enzyme activity and gut bacterial community

Trabajo presentado en Aquaculture Europe 19 (Our future, growing from water), celebrado en Berlín del 7 al 10 de octubre de 2019.The optimization of feeding strategy in relation to the environmental condition needs further investigation in order to maximise performance, fish health and fish quality of Mediterranean farmed species. Environmental temperature during seasonal changes may affects fish metabolism, digestive enzymes activity and gut bacterial community which may exert an effect on performance and tissue composition (Couto et al., 2012; Guerreiro et al., 2016). Data relating interaction between different dietary protein and energy ratio and water temperature changes on digestion condition, gut bacterial community and fat deposition of gilthead seabream fed current aquafeed formulations are scarce. For this reason, the purpose of this study was to evaluate the effects of two dietary protein and dietary energy ratio (DP/DE) during temperature changes on growth, feed efficienc , fat deposition, plasma biochemistry, digestive enzyme activity and gut bacterial community of gilthead sea bream (Sparus aurata).This research was supported by ERC (European Research Council) in MedAID project (Mediterranean Aquaculture Integrated Development), Call H2020-SFS-2016-2017 (Sustainable Food Security – Resilient and resource-efficient value chains), Grant Agreement n. 727315.Peer reviewe