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To elucidate the in vivo endogenous ability of pikeperch (Sander lucioperca) larvae to deacylate and reacylate phospholipids and to elongate and desaturate PUFAs, 20 days post hatch (DPH) fish were incubated with either [1

To elucidate the in vivo endogenous ability of pikeperch (Sander lucioperca) larvae to deacylate and reacylate phospholipids and to elongate and desaturate PUFAs, 20 days post hatch (DPH) fish were incubated with either [1-14C]20:4n-6 bound to PC and PE, or with free [1-14C]-labelled fatty acids (18:2n-6, 18:3n-3, 20:4n-6, 20:5n-3 and 22:6n-3). The modulation capacity of both low LC-PUFAs but high 18C PUFAs precursors dietary supply and increasing salinity on larval fatty acid metabolic pathways was also investigated. [1-14C]DHA was incorporated into larval tissues to a lower extent than [1-14C]ARA or [1-14C] EPA. [1-14C]ARA was significantly less abundant in larval tissues when provided bound to PE than when esterified into PC, indicating that PC is a better phospholipid source to provide LC-PUFA to pikeperch larvae. Radioactivity was mainly recovered into phospholipids, especially that of the three LC-PUFAs ARA, EPA and DHA. All substrates were primarily incorporated into PC except [1-14C]ARA which significantly did into PI. Both [1-14C]EPA and [1-14C]DHA showed a similar esterification pattern into lipid classes: PC > PE > PI > TAG, with [1-14C]DHA presenting the highest esterification into PE of all radiolabelled compounds (26.3% vs 3.6–14.2%). Although higher rearing salinities tended to increase ∆6 desaturase activity, no radioactivity from [1-14C]18:2n-6 or [1-14C]18:3n-3 was detected in ARA or EPA, proving a deficiency of Δ5 activity and the inability of pikeperch to biosynthesize DHA. This work provides novel information on the lipid metabolism of pikeperch at early development necessary for the design of live prey enrichment protocols and dietary formulations adapted to larval metabolic capabilities.

Westernized societies ingest an unhealthy high dietary omega-6/omega-3 fatty acid ratio of 20:1 or even higher. Seafood is the primary source of omega-3 long chain polyunsaturated fatty acids (LC-PUFA) for humans, mainly eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), which are involved in a plethora of physiological and health-related processes. However, the production of marine organisms with aquafeed formulations based on marine ingredients leads to serious environmental impacts on global pelagic fish resources, resulting in an unsustainable activity. The present study aims to gain further insight into the metabolism of fatty acids in chicken as a potential supply for omega-3 LC-PUFA. To this purpose, lipid classes and fatty acid profiles of thighs and hepatocytes, and the modification of [1-14C]18:3n-3 by hepatocytes isolated from three dual-purpose chicken breeds adapted to free-range culture systems were determined. Arachidonic acid highly accumulated in thighs meat (7.16-8.79%) despite being barely supplied in the diet, with DHA (1.22-1.71%) and n-3 docosapentaenoic acid (DPA, 22:5n-3; 1.02-1.14%) being also relevant. Our experimental design with radiolabeled fatty acids was validated for the first time in terrestrial vertebrates. Chicken hepatocytes incubated with [1-14C]18:3n-3 produced a wide variety of C18-C24 intermediates demonstrating that the set of fatty acyl desaturases and elongases enzymes necessary to metabolize dietary C18 precursors are active for the production of LC-PUFA, including EPA, n-3 DPA and DHA.

The in vivo ability of Atlantic halibut (Hippoglossus hippoglossus) larvae to incorporate, de-acylate and re-acylate [1-14C]fatty acids (FA) into lipid classes and to elongate and desaturate those substrates was elucidated. To this purpose, 30 days post-first-feeding (30 dpff) larvae were incubated in the presence of either free [1-14C]-FAs (18:2n-6, 18:3n-3, 20:4n-6, 20:5n-3 and 22:6n-3), [1-14C]18:1n-9 bound to mono- (MAG) and triacylglycerols (TAG), or [1-14C]20:4n-6 bound to phosphatidylcholine (PC) and phosphatidylethanolamine (PE). Halibut larvae can efficiently incorporate dietary FAs through MAG, while FA incorporation when provided as free FAs and especially bound to TAG or phospholipids seems to be very low. These results suggest that lipid digestion might be a limiting factor in the FA absorption and incorporation by 30 dpff Atlantic halibut. The present study also shows that esterification into phospholipids is a strong metabolic fate for dietary long-chain polyunsaturated fatty acids (LC-PUFAs), and the capacity of 30 dpff Atlantic halibut larvae to metabolize dietary FAs through elongation/desaturation processes. Nonetheless, neither EPA nor DHA were detected from [1-14C]ALA, indicating a reduced capacity to biosynthesize these LC-PUFAs and the necessity for them to be adequately supplied through the diet for proper larval development.

The aim of the present study was to determine the effect of Artemia metanauplii endogenous fatty acid (FA) metabolism in the actual availability of dietary essential fatty acids (EFA) for Octopus vulgaris paralarvae development. To this end, both Artemia metanauplii inherent radiolabelled FA metabolism and the Octopus vulgaris paralarvae FA metabolism, after being fed with Artemia metanauplii incubated with radiolabelled. FAs, were determined. Metanauplii were incubated in tissue culture plates during 12 h, with 0.3 mu M of a [1-C-14]FA, including either 18:3n-3, 20:4n-6 (ARA), 20:5n-3 (EPA) or 22:6n-3 (DHA), added individually to separate wells as their potassium salts bound to bovine serum albumin. A total of 3600 one-day-old paralarvae were reared up to 24 h in order to ensure the ingestion of a minimum amount of the labelled Artemia. Paralarvae rearing was performed in 4 L cylinder conical tanks at a density of 25 paralarvae L-1. Labelled Artemia metanauplii were added to each paralarvae rearing tank according to a specific [1-C-14]FA treatment. Artemia in vivo metabolism results showed a preferential catabolism of DHA, which was translated into (1) the lower incorporation of this FA into Artemia total lipids (TL) (2) the highest amount of de novo synthesis of shorter chain-length FAs, as a result of the beta-oxidation of the original DHA substrate. The registered amounts of radiolabelled substrates incorporated into O. vulgaris paralarvae TL fed with labelled Artemia metanauplii were extremely low. Nonetheless, certain amount of intact [1-C-14]ARA and [1-C-14]EPA was recovered into octopus paralarvae TL, and particularly into polar lipid classes, suggesting the possibility of using Artemia as a vehicle to provide ARA and EPA to octopus paralarvae without interfering their bioavailability for the de novo synthesis of phospholipids. On the other hand, and despite of the high amount of [1-C-14]18:3n-3 incorporated into Artemia TL, the FAs with the highest esterification rate into Anemia TAG (18:3n-3 and DHA) were also the lowest incorporated into paralarvae TL. Therefore, the present results suggest that O. vulgaris paralarvae may have a potentially low capacity to metabolise dietary TAG, and so, Artemia may not be the most appropriate vehicle to provide DHA to paralarvae. Spanish GovernmentSpanish Government [AGL2010-22120-CO3] Fundacao para a Ciencia e a Tecnologia (FCT)Portuguese Foundation for Science and Technology [SFRH/BD/76863/2011] FCTPortuguese Foundation for Science and Technology [IF/00576/2014]

Reducing the dependency of fishfeed for marine ingredients and species diversification are both considered crucial factors for the sustainable development of aquaculture. The substitution of fish oil (FO) by vegetable oils (VO) in aquafeeds is an economically feasible solution. However, such substitution may compromise the fish flesh content of essential n-3 long chain polyunsaturated fatty acids (n-3 LC-PUFA) and, therefore, its nutritional value for human consumption. Likewise, there is a wide range of strategies to select new target species for sector diversification, among which, the capacity to biosynthesize n-3 LC-PUFA from their C18 precursors abundant in VO might be considered as a fair preliminary strategy. Therefore, the aim of the present study was to analyze the metabolic fate of [1-14C] labeled 18:2n-6, 18:3n-3, 20:5n-3 and 22:6n-3 in isolated hepatocytes and enterocytes from wild individuals of three fish species with different trophic level: the marine herbivorous salema (Sarpa salpa), the strict carnivorous sand sole (Pegusa lascaris) and the omnivorous thicklip grey mullet (Chelon labrosus). These species were selected for their phylogenetic proximity to consolidated farmed species such as gilthead seabream (Sparus aurata), senegalese sole (Solea senegalensis), and golden grey mullet (Liza aurata), respectively. The study also assessed the molecular cloning, functional characterization and tissue distribution of the fatty acyl elongase (Elovl) gene, elovl5, involved in the biosynthetic metabolism of n-3 LC-PUFA. The three species were able to biosynthesize docosahexaenoic acid (22:6n-3). S. salpa seems to have similar biosynthetic capacity than S. aurata, with a fatty acyl desaturase 2 (Fads2), with Δ6, Δ8 and Δ5 activities. P. lascaris showed a wider Fads2 activity repertory than S. senegalensis, including Δ4 and residual Δ6/Δ5 activities. In C. labrosus, both Δ8 and Δ5 activities but not the Δ6 described for L. aurata were detected in the incubated cells. Elongation from C18 and C20 precursors to C20 and C22 products occurred in hepatocytes and enterocytes as well as in the functional characterization of Elovl5 by heterologous expression in yeast. Elovl5 showed a species specific expression pattern, with the highest rates observed in the liver, gut and brain in S. salpa and P. lascaris, and in the brain for C. labrosus. In summary, the LC-PUFA biosynthesis capacity from S. salpa, P. lascaris and C. labrosus greatly resembled that of their phylogenetic closer species. The three studied species could be further explored as candidates for the aquaculture diversification from their potential ability to biosynthesize LC-PUFA., This study was funded by Ministerio de Economía y Competitividad (AGL2015-70994-R). A. Galindo and M. Marrero are supported by a PhD grant by Cajasiete and Gobierno de Canarias, respectively. Dr. Covadonga Rodríguez and Dr. Ana Bolaños are members of the Instituto de Tecnologías Biomédicas de Canarias (ITB).

The aim of this study was to assess the effect of two rearing conditions: outdoor environment with great volume tanks (500 m3) and low stocking density (~0.4 kg m 3); and indoor environment with smaller volume tanks (10 m3) and higher stocking density (~5 kg m 3), on muscle, liver and ovary lipid composition of Seriola dumerili brood- stock born in captivity. The rearing conditions tested seem to affect the pattern of lipid body depo- sition in broodstock fish of S. dumerili, increasing the muscle and liver triacylglycerides (TG) accu- mulation of fish kept under indoor conditions, probably due to reduced energy expenditure in swimming, with some variations in the fatty acid profile that may respond to the differences in the culture conditions tested. No significant differences were found for Gonadosomatic Index (GSI) or ovary lipid deposition between groups in this study, which may suggest that the conditions tested do not have a major effect on ovary devel- opment. However, one season later the females kept under outdoor conditions released eggs spontaneously, whereas those kept under indoor conditions did not spawn, suggesting that the conditions tested actually have an effect on the broodstock’s reproductive fitness. More studies are needed in order to evaluate whether the condi- tions tested have or not any influence on ovary development., SI

The present study compared the lipid composition and in vivo capability of Artemia sp. metanauplii (the main live prey used in aquaculture) and Grapsus adscensionis zoeae (as a wild zooplankton model) to metabolise unsaturated fatty acids. The two species were incubated in vivo with 0.3 μM of individual [1-14C]fatty acids (FA) including 18:1n‐9, 18:2n‐6, 18:3n‐3, 20:4n‐6 (ARA), 20:5n‐3 (EPA) and 22:6n‐3 (DHA) bound to bovine serum albumin (BSA). Compared to metanauplii, zoeae contained twice the content of polar lipids (PL) and eight-fold the content of long-chain polyunsaturated fatty acids (LC-PUFA). Artemia sp. metanauplii showed increased short chain fatty acid de novo synthesis from beta-oxidation of [1-14C]LC-PUFA, preferentially DHA. Of the LC-PUFA, DHA showed the highest esterification rate into Artemia sp. triacylglycerols. In contrast, in Grapsus zoeae [1-14C]DHA displayed the highest transformation rate into longer chain-length FAs and was preferentially esterified into PL. EPA and ARA, tended to be more easily incorporated and/or retained than DHA in Artemia sp. Moreover, both EPA and ARA were preferentially esterified into Artemia PL, which theoretically would favour their bioavailability to the larvae. In addition to the inherent better nutritional value of Grapsus zoeae due to their intrinsic lipid composition, the changes taking place after the lipid incorporation, point at two distinct models of lipid metabolism that indicate zoeae as a more suitable prey than Artemia sp. for the feeding of marine animals, This work was partially supported by project OCTOPHYS (AGL2010-22120-CO3) funded by Spanish Government. D.B. Reis (SFRH/BD/76863/2011) wishes to thank to Fundação para a Ciência e a Tecnologia (FCT) for her grant. A.V. Sykes is funded by FCT through Programa Investigador FCT 2014 (IF/00576/2014).

The aim of this study was to assess the effect of an experimental diet (ED), with high levels of 18:1 n-9 and low eicosapentaenoic to arachidonic acid ratio (EPA/AA), on the fatty acid (FA) profile of ovary and eggs of Seriola dumerili broodstock, in contrast to a non-specific commercial diet (nsCD), taking wild fish lipid composition as a positive reference. Two groups of Seriola broodstock born in captivity were fed with either the ED or the nsCD during two consecutive spawning seasons (21 months). After 7 months of feeding, fish fed the ED displayed an ovary FA profile much closer to wild fish. During the second spawning season, only the group fed ED released eggs. Egg FA composition showed some minor changes throughout the spawning season, with a marginal reduction of EPA in the late season being the most striking variation. Overall, the use of the ED showed some positive results, which could favor spontaneous egg release from females born in captivity. However, the lack of fertilization and the high level of 18:2 n-6 in the ovary tissue and eggs indicate that further improvements are needed in S. dumerili broodstock diet formulation in order to enhance the reproductive performance of this species in captivity. Practical applications: The use of the ED resulted in an ovary fatty acid profile of cultured females that better resembles that of wild fish. Using broodstock diets with balanced EPA/AA ratios (close to wild fish) may have a positive effect on fish broodstock reproductive performance, at least for this species.

The objective of the present study was to characterise the fatty acid (FA) profiles of the major phospholipids, of Octopus vulgaris and Sepia officinalis hatchlings, namely phosphatidylcholine (PC), phosphatidylserine (PS), phosphatidylinositol (PI) and phosphatidylethanolamine (PE); and to evaluate the capability of both cephalopod species on dietary phospholipid remodelling. Thus, O. vulgaris and S. officinalis hatchlings were in vivo incubated with 0.3μM of L-∝-1-palmitoyl-2-[1-14C]arachidonyl-PC or L-∝-1-palmitoyl-2-[1-14C]arachidonyl-PE. Octopus and cuttlefish hatchlings phospholipids showed a characteristic FA profiles with PC presenting high contents of 16:0 and 22:6n-3 (DHA); PS having high 18:0, DHA and 20:5n-3 (EPA); PI a high content of saturated FA; and PE showing high contents of DHA and EPA. Interestingly, the highest content of 20:4n-6 (ARA) was found in PE rather than PI. Irrespective of the phospholipid in which [1-14C]ARA was initially bound (either PC or PE), the esterification pattern of [1-14C]ARA in octopus lipids was similar to that found in their tissues with high esterification of this FA into PE. In contrast, in cuttlefish hatchlings [1-14C]ARA was mainly recovered in the same phospholipid that was provided. These results showed a characteristic FA profiles in the major phospholipids of the two species, as well as a contrasting capability to remodel dietary phospholipids, which may suggest a difference in phospholipase activities., SI

The transition of Sepia officinalis culture to industrial large scale has been hampered due to bottlenecks related to the limited knowledge on nutritional physiology of the species. Determination of the endogenous ability of S. officinalis hatchlings to metabolise unsaturated fatty acids (FA) may provide new insight on the capability of hatchlings to biosynthesise different FA, as well as lipid classes containing essential fatty acids (EFA). In the present study, cuttlefish hatchlings were incubated with [1-14C]FA including C18 FA (18:1n-9, 18:2n-6, 18:3n-3) and long-chain polyunsaturated fatty acids (LC-PUFA) (20:4n-6 (ARA), 20:5n-3 (EPA) or 22:6n-3 (DHA)), which were added individually as potassium salts bound to bovine serum albumin. As a result, it was possible to investigate the in vivo FA metabolism of S. officinalis hatchlings by following the incorporation of specific [1-14C]FA, which points to the suitability of this methodology to study lipid metabolism of newly hatched cephalopods. The majority of radioactivity incorporated was recovered esterified into polar lipids (PL). A pattern was detected, where [1-14C]DHA, [1-14C]C18 FA and their metabolic products were preferentially esterified into phosphatidylcholine, whereas [1-14C]ARA and [1-14C]EPA were mainly esterified into phosphatidylethanolamine. [1-14C]C18 FA were the most transformed FA with several metabolites produced by elongation and possible desaturation being obtained. As a contrary the radioactivity incorporated into hatchling total lipid (TL) from supplemented [1-14C]LC-PUFA only one elongation product was recovered from the three substrates, except for [1-14C]ARA, where an unidentified product was also detected. The present in vivo results indicated that S. officinalis hatchlings may have capability for the first steps in the biosynthesis of ARA and EPA from 18:2n-6 and 18:3n-3, respectively, including the existence of a desaturase potentially involved. Nonetheless, considering the low desaturation rates detected, this process may not be sufficient to cover EFA demands during development of this species. Therefore, dietary ARA and EPA, as well as DHA, should be supplied during the hatchling stage of Sepia. While designing an inert diet, which ensures normal growth and development of this species during the hatchling stage, the C18 FA and LC-PUFA levels and ratios should be considered, since the esterification pattern detected in the present study suggested competition between these FA for esterification into specific lipid classes. Moreover, considering the observed esterification pattern of LC-PUFA into different lipid classes, it is likely that the DHA/EPA/ARA ratio, rather than DHA/EPA or EPA/ARA ratios, would be of great importance for S. officinalis hatchling development., SI

The high mortalities observed during Octopus vulgaris paralarvae culture have been associated with a nutritional imbalance, with long-chain polyunsaturated fatty acids (LC-PUFA) appearing to have a critical role. In order to determine the in vivo capability of O. vulgaris hatchlings to incorporate and metabolise unsaturated fatty acids (FA), hatchlings were incubated in flat-bottom 6-well tissue culture plates at a density of 90 hatchlings/well in 10mL of seawater (36‰). Incubations were performed with gentle stirring at 21°C for 6h with 0.2μCi (0.3μM) of [1-14C]-labelled FA including 18:1n-9, 18:2n-6, 18:3n-3, 20:4n-6 (ARA), 20:5n-3 (EPA) or 22:6n-3 (DHA), which were added directly to the seawater as their potassium salts bound to bovine serum albumin (BSA). A control treatment without [1-14C]FA was also assessed. O. vulgaris hatchlings not only possessed the ability to incorporate FA bound to BSA, but also to esterify them into phospholipid, with marked specificity. [1-14C]DHA and [1-14C]C18 FA substrates were mainly esterified into phosphatidylcholine, while [1-14C]ARA and [1-14C]EPA were esterified into phosphatidylethanolamine. The majority of radioactivity from [1-14C]FA incorporated into hatchling total lipid was recovered as unmodified FA with elongation being the only metabolism detected. Of the FA investigated, [1-14C]ARA was the most efficiently incorporated into hatchling lipids, but it was also the least modified FA. The fact that no desaturation activity was recorded towards the FA tested in this experiment may indicate that the nutritional requirements of O. vulgaris hatchlings in terms of FA are highly specific and LC-PUFA must be considered essential dietary nutrients. © 2014 Elsevier B.V., This work was partially supported by project OCTOPHYS. Ref. AGL 2010-22120-CO3 funded by the Spanish Government. D.B. Reis (SFRH/BD/76863/2011) and A.V. Sykes (SFRH/BPD/36100/2007) wish to thank Fundação para a Ciência e a Tecnologia for their grants.

The aim of this study was to compare the total lipid (TL) content, the lipid class (LC) composition and their associated fatty acids from muscle, liver and ovary of wild and cultured mature females of greater amberjack ( Seriola dumerili ), in order to obtain information to formulate a more suitable diet for this species broodstock. TL content in muscle and liver was higher in cultured fish than in wild fish, mainly due to TG accumulation, while the ovary TL content was higher in wild fish. Regarding to fatty acids profile, the percentage of 18:1 n -9 in TL and TG was lower in ovaries and muscle of cultured fish than in wild ones. Cultured fish displayed lower proportion of arachidonic acid (20:4 n- 6, ARA) and higher proportions of 18:2 n- 6 and eicosapentaenoic acid (20:5 n- 3, EPA) than wild specimens for all tissues in TL and LC. In contrast, differences in the proportion of docosahexaenoic acid (22:6 n- 3, DHA) between both groups were found only in some tissues and in some LC, being in those cases higher in wild fish. In consequence, cultured fish presented a lower DHA/EPA ratio and a higher EPA/ARA ratio with respect to wild fish. These results suggest that 18:1 n- 9, 18:2 n- 6 and essential fatty acids (EFA), especially EPA and ARA, are not supplied in the appropriate proportions in the diet of cultured fish and could negatively affect their reproductive performance.

Gilthead seabream juveniles were fed on either a fish oil (FO)-containing diet or a diet containing a 50 : 50 blend of FO and Echium oil (EO) to determine the effect of EO on growth, plasma parameters and tissue lipid compositions. After 4 months of feeding, there was a significant increase of 18 : 2n-6 and a reduction of approximately 25% of 20 : 5n-3 in the flesh of fish fed the EO diet. At this point, half of the fish that fed on EO were returned to the FO diet as a third treatment and the trial continued with the three groups for a further 3 months. At the end of the experiment, food intake, survival, growth and plasma parameters were not affected by the inclusion of dietary EO. However, hepatosomatic index (HSI), total lipid and triacylglycerol contents of muscle decreased in fish fed the EO diet. Feeding the EO diet resulted in significant increments of potentially health-promoting fatty acids such as 18 : 3n-6, 18 : 4n-3 and 20 : 3n-6 but reduced n-3 highly unsaturated fatty acids, particularly 20 : 5n-3. When EO-fed fish were returned to the FO diet, tissue lipid contents and HSI tended to increase, but 18 : 2n-6 and 20 : 5n-3 levels were not fully restored to the levels of fish fed the FO diet for the entire trial. Furthermore, the fatty acids present in EO, which may promote beneficial health effects, were reduced. 2

The fatty acid profile of vegetable oils (VOs), together with the poor ability of marine fish to convert polyunsaturated fatty acids (PUFA) to highly unsaturated fatty acids (HUFA), lead to important changes in the nutritional value of farmed fish fed VO, which include increased fat and 18:2n-6 and reduced n-3 HUFA. Echium oil (EO) has a good n-3/n-6 balance as well as an interesting profile with its high content of unusual fatty acids (SDA, 18:4n-3 and GLA, 18:3n-6) that are of increasing pharmacological interest. The effects of substituting 50 % of dietary fish oil (FO) by EO on gilthead seabream (Sparus aurata L.) enterocyte and hepatocyte lipid metabolism were studied. After 4 months of feeding, cell viability, total lipid contents and lipid class compositions were not affected by EO. The cells clearly reflected the fatty acid profile of the EO showing increased SDA, GLA and its elongation product 20:3n-6, and only minorly decreased n-3 HUFA compared to other VO. Metabolism of [1-14C]18:2n-6 and [1-14C]18:3n-3 was also unaffected by EO in terms of total uptake, incorporation, β-oxidation and elongation–desaturation activities.

Epithelial cells were successfully isolated along the intestine of the gilthead seabream using a dissociation method based on intracellular-like solutions. Biochemical and physiological tests revealed highly viable cells from all intestinal segments. Image analysis was used to identify cell types in the epithelial preparations which were highly enriched in enterocytes (95%) over mucous cells. Several digestive hydrolases were determined in the isolated cells. Maltase (M), sucrase (S), leucine aminopeptidase (LA), 5'nucleotidase (5'N), but not gamma-glutamyl transferase (gamma-GT) or alkaline phosphatase (AP) activities were found to be enriched in the epithelial preparations versus the corresponding intestinal homogenates. Comparison of digestive hydrolases revealed the existence of a clear heterogeneity in their expression pattern in the enterocytes, along the intestine. Na(+)-K(+)-ATPase, Na(+)-ATPase and Cl(-)-ATPase activities were also determined in the membrane fraction of isolated cells. Analyses of enzymatic profiles revealed a clear asymmetry in the distribution of all Mg(2+)-dependent ATPases; that is, maximal Na(+)-K(+)- and Na(+)-ATPase activities were observed in the enterocytes from pyloric caeca, while Cl(-)-ATPase activity was about twice as high in the enterocytes from anterior and posterior intestines compared with pyloric caeca. This is the first report demonstrating the existence of heterogeneous metabolic and enzymatic profiles in different enterocyte populations from euryhaline teleosts.