Compound Diets Research Articles

Prediction of digestible protein and lipid contents of crustacean feeds

Due to distinctive feeding habits and digestive physiology determination of nutrient digestibility is more demanding with crustacean than fish species. A study was conducted to validate the use of linear prediction equations established with fish species to predict apparent digestible protein (ADP) and lipid (DL) contents [g kg−1 dry matter (DM)] of feed ingredients (ADP = −10.0731 + 0.8942 CP, DL = −1.5824 + 0.8654 CL) and compound diets (ADP = −51.4001 + 0.9872 CP, DL = −2.7303 + 0.9123 CL) from dietary crude protein (CP) and lipid (CL) contents for crustaceans (shrimp, lobster, crab). Observed values (n = 91) obtained in 17 studies, which evaluated CP digestibility of 26 feed ingredients for eight crustacean species, presented a linear relationship (R2 = 0.9213, RMSE = 54.1245) with predicted values. Predicted values overestimated observed values with a mean prediction error (MPE) of 0.1315. However, observed DL values of 17 feed ingredients (n = 31; studies = 5; species = 5) were overestimated with a MPE of 0.4500. Similar trends than above were found with prediction of the ADP (n = 185; studies = 32; species = 11; R2 = 0.8047; MPE = 0.1002) and DL (n = 64; studies = 11; species = 3; R2 = 0.6907; MPE = 0.2372) contents of compound diets.

Performance, gut morphology and carcass characteristics of fattening rabbits as affected by particle size of pelleted diets

A review of past literature revealed inconsistencies in recommended feed particle size for optimal growth and productive performance of rabbits. Changing diet formulation and subsequent processing conditions may improve pellet texture and potentially affect rabbit performance. In the current study, two isoenergetic and isonitrogenous pelleted diets were formulated, which varied in the particle size of the concentrates (2 and 8 mm, respectively). The objective was to evaluate the effect of different particle sizes of compound diets on performance, nutrient utilisation, gut morphology, and carcass characteristics of fattening Italian White breed rabbits. The finely ground diet led to a significant improvement in feed efficiency and apparent digestibility of crude protein, ether extract, crude fibre and NDF, without any negative effect on gut morphology. Furthermore, a smaller particle size of concentrates in pelleted diets improved carcass traits. Meat colour parameters showed significant differences in longissimus lumborum and biceps femoris due to dietary treatments, but in both muscles pH values 1 h and 24 h after slaughter remained unchanged. It is concluded that a finely ground pelleted diet can be used to improve growth performance of rabbits without affecting carcass parameters.

NUTRITIVE VALUE OF RAW MATERIALS FOR RABBITS: EGRAN TABLES 2002.

Feedstuff tables are presentad including the composition and the nutritive value of 53 raw materials used in compound diets for intensively reared rabbits. Each raw material is characterised by 23 analytical data and its digestible protein and energy values. Because of the importance of the fibre fractions in the nutrition of the rabbit, special efforts have been done to characterise the carbohydrate complex. The digestibility data were selected after a compilation of original literatura data and a discussion between the authors. The methodology used, in the different in vivo assays, was evaluated accurately in order to judge the reliability of the data. Besides digestible and metabolisable energy values are also presentad because they lead to a better mutual comparison between raw materials for formulation purposes. Finally, attention has been drawn that the presentad nutritiva values fit well with the proposed nutrient composition and show coherence in each category of feedstuffs.

EFFECT OF FEEDING A COMPOUND DIET BASED ON NON-CONVENTIONAL FEEDSTUFFS ON GROWTH AND CARCASS CHARACTERISTICS OF RABBITS.

Thirty weaner rabbits were randomly allocated to three diets: a laboratory formulated diet based on extruded soybean meal, groundnut haulms, maize and rice­milling by-products, and designated compound diet, a commerc1al rabbit pelleted diet and a commercial poultry grower's mash. Feed and water were supplied ad /ibitum. The compound diet elicited significantly (P<0.05) higher weight gains (15.2 g/d vs 13.4 or 6.3 g/d), feed consumption, feed conversion efficiency and total edible viscera weight compared to the commercial preparations. The dietary effect on the dressing percentage and relative organ and tissue weights was non significant (P>0.05). These results showed that cost-effective rabbit diet coufd be formulated from extruded soybean meal, groundnut haulms, and by-products of the milling of maize and rice.

A comparison of the occurrence of common dental abnormalities in stabled and free-grazing horses

The purpose of this study was to gain evidence on the prevalence of dental abnormalities in stable-kept horses in comparison with free-living horses. It is expected that free-living horses that graze for as much as 16 h/day will have fewer dental abnormalities than stable-kept horses. In this study, the latter group was fed a diet that was based on a relatively high-energy, cereal-based feed. This was thought to be a representative of common practice in domesticated, stable-kept horses. Compound diets such as this have previously been shown to increase the frequency of chewing cycles and decrease mediolateral excursion. The occurrence of 10 named dental abnormalities present in the dentition of 60 Thoroughbred-type horses was recorded. Half of the population was at grass all year round in New South Wales, Australia. The remainder were stabled for 24 h/day in Gloucestershire, UK. All horses were between 5 and 15 years of age. The same, experienced, equine dental technician examined all horses using a full-mouth speculum and produced a routine dental chart. Stable-kept horses had a significantly higher total occurrence of abnormalities (P < 0.001) than free-living horses. The stable-kept group had a significantly higher prevalence of exaggerated transverse ridging across the occlusal surface of the cheek teeth, focal or ramped overgrowths of the cheek teeth and periodontal disease (P < 0.01 in all cases). All horses in both groups had some occurrence of sharp edges of the buccal and lingual edges of the cheek teeth. The results are in agreement with anecdotal evidence that a fibre-based, grazed diet results in fewer dental abnormalities. However, sharp edges may occur even with what is perceived as a ‘natural’ diet.

Apparent digestibility of compound diets with increasing levels of perilla (Perilla frutescens L.) seeds in rabbit

The aim of this study was to determine the effects of three levels (0, 5 and 10%) of perilla (Perilla frutescens L.) seeds (PFS), included in isonitrogenous and isocaloric diets, on the apparent digestibility in rabbit aged of 73 days. The trial was carried out on 30 crossbred (Carmagnola Grey x New Zealand) rabbits randomly divided in three groups of ten animals each (five male and five female rabbits). Each of them was kept in individual cages. The faeces were collected during the last week of a growing trial that lasted 50 days. No obvious health problems were encountered during the experiment and no rabbits died during the trial. The measured parameters were digestibility of dry matter, organic matter, crude protein, ether extract, neutral detergent fibre, acid detergent fibre and gross energy. The only parameter that was modified by the inclusion of PFS was the ether extract digestibility; it resulted higher in the 10% PFS diet (83.9%) than in the other two diets. Perilla seed may be used satisfactorily as a nutrient supplement for rabbits at levels of up to 10% in the diet with a better digestibility of ether extract than in the other two diets.

The error associated with the prediction of digestible protein contents of fish diets from tabulated values

Numerous species available for culture, and lengthy, tedious and demanding digestibility experiments necessitate the use of tabulated values to calculate the apparent digestible nutrient contents of compound fish diets. The error associated with the above practice was evaluated in the present study with the use of apparent protein digestibility coefficients (APDCs) and dietary crude protein (CP) contents obtained in independent studies on fish nutrition. Prediction of APDCs of 21 compound diets evaluated in 18 studies with rainbow trout (&lt;I&gt;Oncorhynchus mykiss&lt;/I&gt;), by using APDCs of 27 individual feed ingredients determined for this fish species, presented a mean prediction error (MPE) of 0.0489 between observed and predicted values. However, the above APDCs resulted in an overestimation of 7.86% (MPE = 0.0899) for APDCs of compound diets (&lt;I&gt;n&lt;/I&gt; = 15) tested with 7 species other than rainbow trout. The CP contents of the above compound diets were overestimated with MPE’s of 0.3029 and 0.3200 for rainbow trout and other species, respectively, when using CP contents of individual feed ingredients as predictors. This eliminates the use of tabulated values to calculate apparent digestible protein contents of compound fish diets, except if databases are regularly updated with CP values for feed ingredients used.

Accuracy of the use of energy conversion factors for compound fish diets

Conversion factors of 23.6, 39.5 and 17.2 MJ/kg for protein, lipid and carbohydrate contents, respectively, are frequently used in fish studies to calculate the gross energy (GE) content of compound diets. Values predicted according to the above resulted in linear relationships of observed GE values with similar R 2 and mean prediction error (MPE) values when using either nitrogen-free extract (NFE) (R 2 = 0.5713, RMSE = 1.3134, MPE = 0.0741, n = 129, 32 studies) or starch (R 2 = 0.5665, RMSE = 1.6768, MPE = 0.0839, n = 190, 45 studies) as measurements of carbohydrate content. Apparent digestible carbohydrate content (either NFE or starch) was found to be linearly-related (R 2 values of 0.7531 and 0.7460, respectively) to its dietary content in compound fish diets. Predicted apparent digestible protein (ADP), lipid (DL) and carbohydrate contents, together with energy conversion factors, presented R 2 and MPE values of 0.6205 (RMSE = 1.2606) and 0.2051, respectively, between observed and predicted apparent digestible energy (ADE) content with NFE as measurement of carbohydrate content (n = 97, 17 studies, eight fish species). However, with carbohydrates quantified by starch content, an R 2 value of 0.7017 (RMSE = 1.7556) and MPE of 0.1055 were obtained (n = 37, 10 studies, five fish species).

Natural stable isotopes as indicators of the relative contribution of soy protein and fish meal to tissue growth in Pacific white shrimp ( Litopenaeus vannamei) fed compound diets

The present study aimed to investigate the potential use of the differing natural nitrogen stable isotope ratios in plant- and fish-sourced dietary components in the assessment of their relative utilisation in compound diets. Pacific white shrimp postlarvae (2.0 ± 0.6 mg ww) and juveniles (414 ± 11 mg ww) were fed eight experimental isoenergetic and isonitrogenous diets at each of two protein levels (46 and 23%). Diets were formulated with either fish meal or soy protein isolate as the only protein source, or in ratios of 50:50 and 10:90 based on nitrogen content. Contrasting nitrogen isotopic values ( δ 15N) of the fish meal and soy protein allowed estimation of the relative contribution of both ingredients to muscle tissue growth using an isotopic mixing model. The dietary effects on nitrogen turnover rates and on the isotopic diet–consumer discrimination factors ( Δ 15N) were also assessed. Nitrogen half lives in muscle tissue were estimated from turnover rates and growth after using an exponential model of isotopic change. In all cases, analysis of postlarval and juvenile muscle tissue indicated a biased nutritional contribution from fish meal, so that in postlarval shrimp fed the 46% protein diet containing a 50:50 ratio of the two ingredients, 69% of nitrogen in muscle tissue originated from fish meal; while in animals fed diets containing the 10:90 ratio of the two ingredients, the relative contributions of nitrogen from fish meal and soy protein were 32 and 68%, respectively. Juvenile shrimp fed the same 50:50 diet, incorporated 73% of nitrogen form fish meal and 27% from soy protein. The mixed diets with higher soy inclusion supported growth equivalent to that of the control and fish meal-based diets, possibly due to the disproportionate contribution of fish meal to growth. Muscle tissue of shrimp fed either 100% fish meal or soy-based diets showed contrasting Δ 15N values that were positively correlated to soy protein inclusion level. The magnitude of these values further increased when shrimp were fed diets containing the lower protein level. The results demonstrate the potential for application of natural stable isotope analysis of diets and tissue in evaluation of plant-source ingredients and the optimisation of their use in diets containing very low levels of fish meal.

Characterization of Human Gene Expression Changes after Olive Oil Ingestion: an Exploratory Approach

Olive oil consumption is protective against risk factors for cardiovascular and cancer diseases. A nutrigenomic approach was performed to assess whether changes in gene expression could occur in human peripheral blood mononuclear cells after oli ve oil ingestion at postprandial state. Six healthy male volunteers ingested, at fasting state, 50 ml of olive oil. Prior to intervention a 1-week washout period with a controlled diet and sunflower oil as the only source of fat was followed. During the 3 days before and on the intervention day, a very low-phenolic compound diet was followed. At baseline (0 h) and at post-ingestion (6 h), total RNA was isolated and gene expression (29,082 genes) was evaluated by microarray. From microarray data, nutrient-gene interactions were observed in genes related to metabolism, cellular processes, cancer, and atherosclerosis (e.g. USP48 by 2.16; OGT by 1.68-fold change) and associated processes such as inflammation (e.g. AKAP13 by 2.30; IL–10 by 1.66-fold change) and DNA damage (e.g. DCLRE1C by 1.47; POLK by 1.44fold change). When results obtained by microarray were verified by qRT-PCR in nine genes, full concordance was achieved only in the case of up-regulated genes. Changes were observed at a real-life dose of olive oil, as it is daily consumed in some Mediterranean areas. Our results support the hypothesis that postprandial protective changes related to olive oil consumption could be mediated through gene expression changes.

Nutrient Digestibility of Cereal Grain Products and By‐products in Extruded Diets for Nile Tilapia

Abstract Apparent digestibility coefficients (ADCs) provide estimates of nutrient availability in feedstuffs and can be used as a tool for selecting ingredients to compound cost‐effective diets for fish. Extrusion process is one factor that could influence ADC values. Thus, a digestibility trial was undertaken to evaluate ADC of protein, energy, and dry matter, and apparent amino acid availability (AAAA) in five cereal grain products/by‐products (corn, wheat middlings, broken rice, rice bran, and sorghum) in compounded diets for Nile tilapia. Chromic oxide was used as an external inert marker. The digestibility values of energy and dry matter in ingredients, in decreasing order, were highest for broken rice (95.34 and 96.45%), sorghum (82.37 and 87.29%), corn (67.34 and 82.21%), rice bran (57.58 and 55.59%), and wheat middlings (48.94 and 45.88%). Protein digestibility value was higher for corn (72.86%) and the lowest value was observed for sorghum (56.77%), while broken rice, wheat middlings, and rice bran presented values ranging from 63.01 to 66.88%. AAAA values were higher for corn (70.05%) and the lowest methionine and cystine availability values were recorded for wheat middlings and broken rice, respectively. Broken rice appears as one of the most indicated ingredient for using in Nile tilapia diets because of its highest values of nutrient digestibility when compared to the other energetic sources. The use of this information should aid more precise and economic diet formulation for Nile tilapia.

Linear models to predict the digestible lipid content of fish diets

Values for the digestible contents of nutrients in diets and feed ingredients are of utmost importance in nutritional strategies for fish. Prediction from dietary composition would eliminate lengthy, tedious and demanding digestibility experiments with fish. Apparent digestible lipid (DL) content [range 7.6–353.4 g kg−1 dry matter (DM)] in compound diets can be predicted with high accuracy (n = 610; studies =127; fish species = 34; R2 = 0.9515; RMSE = 16.9504) from dietary crude lipid (CL) content (range 12.0–388.7 g kg−1 DM) by the linear regression equation DL =−2.7303 + 0.9123 CL. Validation of this equation against 65 values from 15 independent studies presented R2 and mean prediction error (MPE) values of 0.9947 and 0.0671, respectively. The corresponding equation for 37 individual feed ingredients evaluated in 24 studies with 18 fish species (n = 180) was found to be DL = −1.5824 + 0.8654 CL (R2 = 0.9717; RMSE = 8.3765). However, validation of the latter is currently hampered by a lack of independent values.

The use of linear regression to predict digestible protein and available amino acid contents of feed ingredients and diets for fish

An aquatic environment and unique biological characteristics complicate the determination of apparent digestible protein (ADP) and apparent available amino acid (AAAA) contents of feed ingredients and diets for fish. This urges for alternative methods of calculation, such as prediction from dietary chemical composition. Analysis of 617 means from 69 studies, which evaluated the protein digestibility of 73 feed ingredients with 35 fish species, revealed a linear relationship (ADP = − 10.0731 + 0.8942 CP, R 2 = 0.9462) between dietary crude protein (CP; g/kg dry weight) and ADP (g/kg dry weight) contents. In compound diets ( n = 831, 170 studies, 49 fish species) this relation was described by ADP = − 51.4001 + 0.9872 CP ( R 2 = 0.8632). Validation of the above with values from independent studies presented a high degree of agreement ( R 2 > 0.8000; mean prediction error < 0.1100) between predicted and determined values. AAAA profiles in feed ingredients and compound diets, expressed as g/kg dry weight, are predictable ( R 2 mostly > 0.9500) from its dietary amino acid contents through linear regression. The above equations provide a useful tool that could be use in practical feed formulation for fish. However, further work is needed on the validation and development of the prediction of AAA contents.

Ontogeny of the digestive tract of thick lipped grey mullet ( Chelon labrosus) larvae reared in “mesocosms”

This work describes the ontogeny of the digestive tract in thick lipped grey mullet ( Chelon labrosus) larvae reared until day 36 post-hatching with the semi-extensive technology in mesocosms. Diet was constituted by live preys, rotifers, Artemia and wild zooplankton, then compound diet was added from day 20 (p. h.). Linear growth, weight growth and digestive enzymes specific activities were studied during larval ontogeny. Pancreatic enzymes (trypsin and amylase) and intestinal enzymes (leucine-alanine peptidase “Leu-ala”, aminopeptidase N “AN” and alkaline phosphatase “AP”) were assayed in larvae sampled throughout the rearing trial to evaluate gastrointestinal maturation along the development. The trypsin specific activities were very high during the first two weeks and then declined as observed in marine fish species. A following increase in trypsin specific activity from day 20 was attributed notably to ingestion of particle compound diet. In contrast to the pattern generally described in fish larvae, amylase specific activity showed a continuous increase. This could be attributed to the fact that C. labrosus is an omnivorous species and suggests that the fish might be able to use efficiently diets containing higher levels of starch or other carbohydrates since the end of larval development. Relative expression of intestinal brush border membrane enzymes (AP and AN) and cytosolic enzyme (Leu-ala), showed an abrupt increase of both AP/leu-ala and AN/leu-ala ratios at day 8 (p. h.), indicating that maturation of intestinal tract in C. labrosus larvae is particularly precocious. It is assumed that larvae of C. labrosus might support early co-feeding and weaning strategies, which could reasonably be initiated since mouth opening.

Rumen digestion and microbial protein synthesis by growing lambs fed high-concentrate diets: Effects of cereal processing and animal age

Rumen digestion and microbial protein synthesis were studied using 36 growing lambs given either free choice access to separate feeders with whole barley grain and a pelleted soybean meal-based supplement (treatment WB) or a pelleted compound feed (treatment C) made by combining ground barley (0.65) with the same protein supplement (0.35). Free access to barley straw was offered in treatment C but not in WB. While both treatments were imposed before and after weaning (at 42 days), for a third treatment the compound feed was replaced after weaning by whole barley grain and the protein supplement without access to straw (treatment CWB). Six lambs from each treatment were slaughtered at 10 and 30 days post-weaning after 15N-labelling of microbial N and abomasal digesta flows were estimated using C 31 alkane as marker. Processing of barley grain increased (P<0.05) the apparent digestibility of dry matter in the rumen irrespective of age (0.53, 0.48 and 0.43 (S.E. 0.027) for C, CWB and WB). Ruminal pH averaged 5.5 (S.E. 0.06) regardless of cereal processing. The molar ratio of acetate to propionate decreased with age reflecting a higher proportion of grain in the mixed diets (WB and CWB) at 30 than 10 days post-weaning. Even with similar dietary proportions of grain and protein supplement, the acetate to propionate ratio was lower for lambs fed the free-choice (WB and CWB) vs. those fed the compound (C) diet (1.3 vs. 2.2 (S.E.D. 0.37)). Ruminal ammonia concentration increased with age and was lower for treatment C compared with treatments WB and CWB (24 vs. 127 (S.E.D. 22.2) mg/L), reflecting the higher protein intake of the latter two treatments. However, recovery of N intake as abomasal non-ammonia N was low for all treatments due to high protein intake and inefficient microbial growth compared to values reported for mixed diets. The efficiency of microbial N synthesis did not differ between treatments but it was negatively correlated ( r = −0.73) with the organic matter apparently digested in the rumen, resulting in similar microbial yields in spite of the lower digestion in the rumen of whole barley diets. Feeding whole barley is thus a useful strategy to modify the site of digestion in intensive lamb fattening, allowing to reduce ruminal fermentation without depressing microbial N yield.

Phospholipids vs. neutral lipids: Effects on digestive enzymes in Atlantic cod (Gadus morhua) larvae

The aim of this study was to evaluate the effect of dietary lipid classes (phospholipid vs. neutral lipid) and level of n-3 highly unsaturated fatty acids (HUFAs) on growth, survival and digestive enzymatic activity in Atlantic cod (Gadus morhua) larvae. Larvae were fed enriched rotifers from mouth opening and were weaned to formulated diets during a co-feeding period lasting from 17 days post hatch (dph) to 24 dph. Larvae were fed exclusively compound diets from 24 dph until the end of the experiment. Three isoproteic and isolipidic compound diets with gradually decreasing levels of DHA and EPA in the dietary phospholipid fraction (diet PL3>PL1>NL1) and increasing levels of total dietary neutral lipids (PL3<PL1<NL1) were used. Larvae fed the PL3 or PL1 had a significant higher dry weight than larvae fed the NL1 diet at the end of the experiment (45 dph). Survival did not differ significantly between treatments. A gut maturation index based on the relation between the amount of the brush border enzyme alkaline phosphatase and the cytosolic enzyme leucine-alanine aminopeptidase showed that the enterocyte maturation on 35 and 45 dph was better in larvae fed the PL3 and PL1 diet than larvae fed the NL1 diet. Dietary composition did not significantly affect the activity of α-amylase, but an age specific decrease in activity was observed. The dietary composition did affect the specific activity of trypsin, although showing variation in pattern between different larval ages at sampling. The activity of neutral lipase showed high variability between dietary treatments, but at the end of the experiment the specific activity of neutral lipase was positively connected to the dietary neutral lipid levels. The results from this study showed that cod larvae use DHA and EPA in the phospholipid fraction more efficiently compared to those in the neutral lipid fraction.

Effects of Dietary Short‐chain Fructooligosaccharides on Intestinal Microflora, Survival, and Growth Performance of Juvenile White Shrimp, Litopenaeus vannamei

Abstract.— Five groups of juvenile white shrimp, Litopenaeus vannamei, in triplicate were separately fed a compound diet with additional short‐chain fructooligosaccharides (ScFOS, Profeed® 95%) 0, 0.4, 0.8, 1.2, or 1.6 g/kg dried diet for 8 wk to investigate the effects of ScFOS on the intestinal microflora, survival, and growth performance of the shrimp. The juvenile shrimp with around 0.17 g of initial body weight were divided into 30 per tank and reared in a standard water recirculation system at 28 C. The shrimp were fed five times a day. At the end of experiment, the shrimp were weighed and their intestinal samples were analyzed for the amounts of Vibrio parahaemolyticus, Aeromonas hydrophila, Lactobacillus sp., and Streptococcus faecalis using selective agar. The results showed that the shrimps’ weight gain and specific growth rate increased with the increment of dietary ScFOS, while their feed conversion ratio decreased. The result was the best when an additional ScFOS 0.4 g/kg dried diet was used.

The problem of meeting dietary protein requirements in intensive aquaculture of marine fish larvae, with emphasis on Atlantic halibut (Hippoglossus hippoglossus L.)

Atlantic halibut (Hippoglossus hippoglossus) achieve a mature gastrointestinal tract approximately 2 months after first feeding (12 °C). The immature digestion may be the reason that compound diets fail to sustain growth and survival in first feeding halibut larvae and in larvae of other marine fish species. On the other hand, larvae fed with live feeds are capable of extraction of sufficient quantities of nutrients to sustain high growth rates. A lower availability of the protein in formulated diets compared with live prey is considered to be an important reason for the low performance of formulated diets. One approach to increase dietary protein availability is supplementation of pre-digested proteins. Experiments using tube fed individual larvae show that halibut larvae are able to utilize hydrolysed protein more efficiently than intact protein. However, Atlantic halibut in culture did not respond well to dietary supplementation of hydrolysed protein, in contrast to some other species. One reason may be extensive leaching of pre-hydrolysed proteins from the microparticulate feed. Atlantic halibut are slow feeders and may thus suffer more from nutrient leaching than species eating more rapidly. Feed formulation techniques affect dietary protein leaching, and in this paper, different techniques and their impact on feed properties are described. Microbound diets are most widely used in larval rearing, but show high rates of nutrient leaching. Lipid-based capsules seem to have the best potential to prevent leaching, however, they are not able to deliver a complete diet. The high need for improvements in larval feed formulation techniques are clearly stated, and some suggestions are given. Among these are production of complex particles, where small lipid-based capsules or liposomes containing the low molecular weight water-soluble nutrients are embedded. In such feed particles the water-soluble molecules are protected from leaching. Techniques for delivery of water-soluble nutrients that are needed in large quantities, i.e. free amino acids or hydrolysed and water-soluble protein, remain to be developed.

Dietary modulation of some digestive enzymes and Metabolic processes in developing marine fish: Applications to diet formulation

During these last 20 years, many studies have focussed on the development of the digestive tract in marine fish larvae. Most of the studies aimed at acquiring knowledge on the optimal form of dietary supply for different nutrients, in order to formulate a compound diet able to totally replace live preys in the fish larvae feeding sequence. Consequently, most of the studies aimed at describing the effect of dietary adaptation on digestive enzymes profile, the morphology of the main organs, while others aspects of the physiology of the larvae digestive tract (gut hormones, intestinal transport…) were poorly investigated. This review reports the more recent data on dietary modulation of digestive enzymes with a particular emphasis, when possible, on the molecular and hormonal mechanisms controlling enzyme expression in larvae. We examined how the dietary modulation of pancreatic and intestinal enzymes involved in protein digestion can provide useful information concerning the nature and molecular form of a dietary protein supply that would be adequate for larval stages. In the same way, data on lipase and phospholipase A2 paralleled with recent findings on lipid transport, strongly suggests that fish larvae handle phospholipids better than triglycerides. A new field of research has been opened in fish larvae nutrition, with the study of the effects of some nutrients on the functioning of some metabolic pathways involved in development and their impact on larvae physiology and morphogenesis, as well as the further development of juveniles. These studies revealed cross-talks between some metabolic processes, particularly those concerning vitamin A and polyunsaturated fatty acids, during fish larvae development and unveil the necessity to design a global approach for determining the requirements of some nutrients.

Is it possible to influence European sea bass ( Dicentrarchus labrax) juvenile metabolism by a nutritional conditioning during larval stage?

The purpose of this study was to check if it is possible to influence sea bass juvenile metabolism by a conditioning of larvae from day 6 post hatching to day 45 to a low or a high HUFA compound diet (LH, 0.8% EPA + DHA and HH, 2.2% EPA + DHA) when reared at 16 or 22 °C. Following a 3-month intermediate period (at 19 °C using a commercial diet), the adaptability of the 4 initial larval groups to a HUFA experimental deprived diet (0.5% EPA + DHA) were tested at 19 °C in a 60 day-experiment (d-151–211). The four experimental duplicated conditions were ex-LH16 and ex-HH16 for the 2 groups previously reared at 16 °C (initial weight, 7.3 ± 0.5 g) and ex-LH22 and ex-HH22 for the 2 groups previously reared at 22 °C (initial weight, 11.1 ± 0.5 g). Survival was maximal and there was a 1.6–2 fold increase in mass during the experiment. Growth was similar in the 4 experimental groups: NS difference in growth curve slopes ( P = 0.7). At the end of the experiment (d-211), whole body fat levels were in the same range in all groups (13–15% WW). The fatty acid (FA) composition in polar lipids (PL) and total lipids (TL) were significantly affected by initial weight related to larvae conditioning, which can be mainly attributed to a dilution effect (impact of initial FA content on final FA content versus relative mass increase during the course of the experiment). Conversely to this trend, DHA content in PL was higher in the ex-LH groups than in the ex-HH groups whatever thermal conditioning of larvae was. This indicated that ex-LH groups had a better capacity to adapt to a deficient HUFA diet than ex-HH fish. The relative expression of the delta-6 desaturase (Δ6D) was significantly higher in ex-LH than in ex-HH groups ( P < 0.001) between d-151 and d-181, which suggested that Δ6D transcription in ex-LH groups was positively modulated by the HUFA-deprived diet. This stimulation of the first step of the desaturation/elongation pathway could allow synthesizing FA needed to compensate low dietary HUFA supply. This study shows for the first time that it seems possible to influence juvenile fish metabolism by a nutritional conditioning during the larval stage.