P. Badía

Influence of broodstock gilthead seabream (Sparus aurata L.) dietary fatty acids on egg quality and egg fatty acid composition throughout the spawning season

The influence of broodstock dietary lipids on egg quality and egg fatty acid composition throughout the spawning season of gilthead seabream was investigated. For this purpose, the fish were fed for 7 months either a control diet (diet C) or a diet deficient in n−3 highly unsaturated fatty acids (n−3 HUFA) but rich in both oleic (18:1n−9) and linolenic (18:3n−3) acids (diet D). Eggs spawned by both groups of fish were sampled at the beginning, middle and end of the spawning season and the fatty acid composition of their neutral (NL) and polar lipids (PL) determined. In the early season, percentages of fertilized and hatched eggs, relative proportions of NL and PL as well as their fatty acid compositions, were not affected by the lipid composition of the broodstock diet. However, the eggs spawned during the middle and late seasons showed marked differences among the two groups of fish, clearly reflecting the influence of dietary fatty acids. This influence was more evident in the neutral lipid fraction than in the polar lipids. No correlation was found between the number of buoyant eggs and eicosapentaenoic (20:5n−3, EPA), docosahexaenoic (22:6n−3, DHA) fatty acids or total n−3 HUFA contents in egg phospholipids. However, a negative correlation was detected when percentages of fertilized eggs were compared with the levels of 18:1n−9, 18:3n−3 and with the ratio 18:1n−9/n−3 HUFA present in the phospholipids. Our results indicate the importance of maintaining not only the level of n−3 HUFA in egg membrane phospholipids, but also the balance between n−3 HUFA and other fatty acids such as 18:1n−9 and 18:3n−3, in order to obtain a high spawning quality.

Lipid and fatty acid composition of ovaries from wild fish and ovaries and eggs from captive fish of white sea bream (Diplodus sargus)

Abstract The fatty acid composition of ovaries from wild white sea bream and ovaries and eggs of captive white sea bream were investigated to estimate the fatty acid requirements of this species. The total lipid (TL) content in wild fish ovaries was similar to that found in ovaries and eggs from captive fish. The general pattern of the fatty acid distribution in lipid of ovaries from wild fish and ovaries and eggs from captive fish was similar. In total lipid, no significative differences in total monoenes, n −6, n −3 and n −3 highly unsaturated fatty acids (HUFA) were found. However, the relative percentage of specific fatty acids differed between wild and captive fish. Thus, arachidonic acid (20:4 n −6, AA) percentage was higher in wild ovaries than in ovaries and eggs from captive fish, whereas eicosapentaenoic acid (20:5 n −3, EPA) showed the opposite trend. In consequence, wild fish presented a lower EPA/AA ratio in their ovaries when compared with ovaries and eggs of captive fish. These differences were extended to all lipid classes studied (triacylglycerol (TG), phosphatidylcholine (PC) and phosphatidylethanolamine (PE)). The present study suggests that essential fatty acids, specially EPA and AA of the diet supplied to the captive white sea bream broodstocks, do not seem to be in an appropriate proportion for this species.

The n-3 highly unsaturated fatty acids requirements of gilthead seabream (Sparus aurata L.) larvae when using an appropriate DHA/EPA ratio in the diet

Abstract Three day-old Sparus aurata larvae were fed rotifers ( Brachionus plicatilis ) previously enriched with four lipid emulsions containing different percentages (10–30%) of n −3 highly unsaturated fatty acids (HUFA) but a fixed docosahexaenoic (DHA; 22:6 n −3) to eicosapentaenoic acid (EPA; 20:5 n −3) ratio of about 2/1. The n −3 HUFA content of the enriched rotifers varied from 0.9 to 3.0% on a dry weight basis (DWB). In addition, the four groups of rotifers displayed a constant DHA/EPA ratio of around 1.4/1. After 7 days of feeding, no significant differences in larval growth were observed among the treatments. One week later, larval total length was significantly improved by the elevation of the n −3 HUFA level in the diet from 0.9 to 1.5% DWB, with further increment not exerting any apparent effect on larval development. There was some loss of total lipids in the larvae during the first week of feeding which particularly affected the levels of n −3 HUFA in the polar lipid fraction. These losses were clearly restored from day 7 to 14 of feeding. At the end of the experimental period, larvae fed rotifers contributing less n −3 HUFA, contained lower levels of total and polar lipids, as well as lower levels of n −3 HUFA in the polar lipids. In conclusion, under our experimental conditions, the minimum requirement for n −3 HUFA of 17 day-old S. aurata larvae appears to be met by 1.5% in rotifers DWB, almost four times less than the value previously reported by our group when using rotifers with DHA/EPA ratios 2–3 times less favourable to DHA than to EPA.

Influence of n-3 highly unsaturated fatty acid deficiency on the lipid composition of broodstock gilthead seabream (Sparus aurata L.) and on egg quality

A feeding experiment was conducted on gilthead seabream (Sparus aurata) broodstock to investigate the incidence of n-3 highly unsaturated fatty acids (n-3 HUFA) dietary deficiencies on the lipid composition of female liver, gonads and eggs, in relation to spawning quality. Broodstock were fed a control (C) diet or a n-3 HUFA deficient (D) but linolenic acid rich diet. After 20 weeks of feeding, the results showed that levels of total neutral (TNL) and total polar (TPL) lipids of female gonads and eggs were independent of diet. However the fatty acid composition of phosphatidylcholine (PC), phosphatidylethanolamine (PE) and phosphatidylinositol (PI) of female liver, gonads and eggs in the two groups of fish showed marked differences, reflecting the influence of fatty acid levels in the broodstock diets. This influence was even higher in TNL than in the phospholipid classes examined. In fish fed n-3 HUFA deficient diet, fatty acid composition of TNL of female gonads and eggs reflected the diet more than liver. A higher egg production in broodstock fed C diet (1.8% n-3 HUFA in diet) was extended to spawning quality such as percentages of fertilised and hatched eggs.

Influence of eicosapentaenoic to docosahexaenoic acid ratio (EPADHA) of dietary lipids on growth and fatty acid composition of gilthead seabream (Sparus aurata) juveniles

Abstract A feeding experiment was conducted to investigate the influence of eicosapentaenoic acid (20:5n − 3; EPA) to docosahexaenoic acid (22:6n − 3; DHA) ratio ( EPA DHA ) of dietary lipids on growth and fatty acid composition of gilthead seabream juveniles. Fish were fed three diets containing the same amount of total n − 3 highly unsaturated fatty acids (n − 3 HUFA) but different EPA DHA ratios. No mortality was observed during the feeding trial, but significant differences were found in growth rate. The best growth rate and lowest hepatosomatic index was obtained in fish fed a diet containing an EPA DHA ratio of 2 1 . The dietary lipid treatment had no effect on the EPA DHA ratio in neutral lipid of all the tissues studied. However, marked differences in EPA DHA ratio were found in polar lipids of the liver, muscle and gills. It is concluded that, under the conditions employed, an EPA DHA ratio of 2 1 in the diet improves the condition of juvenile gilthead seabream.

Efficacy of dietary methyl esters of n - 3 HUFA vs. triacylglycerols of n - 3 HUFA by gilthead seabream (Sparus aurata L.) juveniles

Abstract A feeding experiment was carried out on gilthead seabream juveniles to investigate the utilization of dietary n −3 highly unsaturated fatty acids ( n −3 HUFA), when presented as methyl esters or as triacylglycerols. Three groups of gilthead seabream juveniles, of an initial mean weight of 62 g, were fed diets containing the same level of n −3 HUFA (about 2% dry weight basis, DWB) but where these essential fatty acids (EFA) were supplied in the form of methyl esters, triacylglycerols or as a mixture of these two chemical forms (diets 1, 2 and 3, respectively). A fourth group of 62-g individuals was fed a diet containing a particularly high level of triacylglycerols of n −3 HUFA (about 5% DWB). After 8 weeks of feeding, the results showed that fish growth, hepatosomatic index, total lipid content, and fatty acid composition of neutral and polar lipids of brain, liver, gills and muscle were not affected by the chemical form of the lipids given in the diet. However, individuals fed the very high level of EFA (diet 4) showed a lower growth rate than the other three groups of fish. In addition, eicosapentaenoic acid (EPA; 20:5 n −3) and docosahexaenoic acid (DHA; 22:6 n −3) levels in both neutral and polar lipids from liver, gills and muscle were higher in this group of fish, with the brain fatty acid composition being less affected by dietary regime.

Mechanisms of transport of Na+ and Cl− in the lizard colon

1. Ionic fluxes of sodium and chloride across lizard colon mucosa were measured and compared with the electrical characteristics of the tissue under voltage-clamped conditions. 2. In a Ringer-bicarbonate solution there was both a net sodium flux (JNanet) and a net chloride flux (JClnet) from mucosa to serosa. The net flux residual (JR) was near zero, indicating that net sodium and chloride transport is the result of an electrically neutral transport mechanism. 3. In the presence of sodium, the net chloride flux was abolished and the short-circuit current (Isc) and the electrical potential difference (PD) were unchanged. In the absence of chloride the net sodium flux was abolished and the short-circuit current and electrical potential difference were not modified. 4. From an analysis of the effects of the inhibitors, furosemide, amiloride and disulfonic stilbene (DIDS), a plausible model was developed to explain the characteristics of sodium and chloride absorption.

Effects of vasopressin on electrolyte transport in lizard intestine

SummaryVasopressin applied serosally had no effect on electrical parameters and unidirectional Na and Cl fluxes across anin vitro short circuited preparation of lizard ileum. Short circuit current (Isc) and transmural potential difference (PD) across colon were decreased by vasopressin and increased by cyclic AMP. Vasopressin increased the mucosal-to-serosal flux of sodium and chloride across short circuited colon. Cyclic AMP had no effect on the rate of Na absorption but reversed Cl absorption to secretion. Vasopressin enhanced the net absorption of water across the colon but had no effect on absorption across ileum. Cyclic AMP activity in homogenates of colon was not altered by vasopressin but was increased by theophylline. It is concluded that the colonic response of the lizard colon to vasopressin is mediated by a noncyclic AMP mechanism.

Intestinal phenylalanine transport in the cultured gilthead bream (Sparus au rata)

Abstract 1. 1. The influx of L-phenylalanine and its effects on the electrophysiology in upper and lower intestine of the cultured fish, Sparus aurata, were measured. 2. 2. The Km and Vmax of l -phenylalanine influx into the tissues were higher in the upper intestine than in the lower intestine. 3. 3. A prominent diffusion-like transport component was also measured in both segments during influx experiments. 4. 4. Addition of l -phenylalanine to the mucosal side of the intestine caused a significant but slow increase in electrical potential difference (PD) and in the short-circuit current (Isc). The increases were dependent on the presence of the sodium ion in the incubation medium. 5. 5. Isc was the hyperbolic function of amino acid concentration characterized by the parameters Vmax (maximum change in Isc) and Km (concentration needed to attain an Isc equal to half the Vmax). 6. 6. Isc-determined Km constants showed slight differences from values obtained from direct measurements of l -phenylalanine uptake into tissue.

Electrical properties of a Na+-dependent phenylalanine transport in Lizard (Lacerta galloti) duodenum

The unidirectional transepithelial fluxes of L-phenylalanine across lizard duodenum were determined in flux chambers. Phenylalanine was preferentially transferred from the mucosal to the serosal fluid. This transport was accompanied by an accumulation of substrate from the mucosal medium into the tissue to a similar level and against a concentration gradient. There was no net movement of phenylalanine when the sodium was substituted by choline. The influx of L-phenylalanine into the epithelial cells of lizard duodenum was examined by incubating slices of intestine in radioactively-labelled solutions of the substrate for 2 min. The steady-state uptake was assessed after similar incubations lasting 45 min. Phenylalanine influx obeys the Michaelis-Menten equation with a Km of 5.1 and is dependent on the presence of sodium ions in the incubation medium. Phenylalanine has been used to induce changes in short-circuit current (delta Isc) across intestine. delta Isc was a hyperbolic function of amino acid concentration characterized by the parameters Jm (maximum change in delta Isc) and Km (concentration needed to attain an delta Isc equal to half the Jm). delta Isc determined Km constants showed good agreement with values obtained from direct measurements of phenylalanine uptake into tissue.