Jean Robin

Total replacement of fish oil by soybean or linseed oil with a return to fish oil in turbot (Psetta maxima): 1. Growth performance, flesh fatty acid profile, and lipid metabolism

The aim of the study was to investigate the replacement of fish oil by vegetable oils and the effects of a washout with a return to fish oil on growth performances and lipid metabolism. Three experimental fish meal-based isonitrogenous (crude protein content: 57.5%) and isolipidic (crude lipid content: 16.5%) diets were formulated containing either 9% of added fish oil (FO), soybean oil (SO), or linseed oil (LO). Each diet was distributed to triplicate groups of 25 marketable size turbot (initial body weight of 579 g) grown in seawater at water temperature of 17 °C. Fish were fed once a day to visual satiety. At the end of the growth trial, which lasted 13 weeks, all groups of turbot were fed with FO diet for 8 weeks. The growth of turbot was high, but the incorporation of vegetable oils in the diets resulted in a slight decrease in growth as compared to those fed with fish oil-based diet. Feed and protein efficiency and whole body composition were not affected by dietary lipid sources. Total lipid content was low in the muscle of turbot (below 2%); ventral muscle being fatter than dorsal muscle. Liver and muscle fatty acid (FA) composition reflected dietary FA composition. Liver and muscle of fish fed with SO diet were rich in 18:2n-6, whereas those of fish fed with LO diet were rich in 18:3n-3. Liver and muscle of fish fed with SO and LO diets had lower levels of 20:5n-3 and 22:6n-3 in comparison to those of fish fed with FO diet. In turbot, hepatic lipogenic enzyme activities were low and not influenced by dietary lipid source. At the end of the second period, after transfer to FO-based diets, muscle FA composition of fish fed previously with SO and LO diets were still different to those of fish fed with FO diet. The values of 18:2n-6 and 18:3n-3, respectively, were lower than the values found at the end of the growth period, but higher than those of fish fed with FO diet. An increase of FA levels, characteristic of fish oil, was observed in the liver and muscle of fish previously fed with vegetable oils. Data obtained show that replacement of fish oil by vegetable oils is possible with negligible impact on growth performance of turbot, that dietary lipids are an effective vector to influence the nutritional quality of finished product, and that a duration of 8 weeks is not sufficient to bring the FA profile of turbot of this size back to that of fish fed with fish oil over the whole period.

Dietary lipid level, hepatic lipogenesis and flesh quality in turbot (Psetta maxima)

A study was undertaken with marketable size turbot to evaluate the effects of dietary fat levels on chemical composition, lipogenesis and flesh quality. Four experimental diets containing graded levels of fish oil in order to obtain 10%, 15%, 20% and 25% of crude fat were fed to triplicate groups of turbot (initial body weight of 660 g) for 12 weeks in full strength seawater at temperature of 17°C. Nutrient digestibility was not influenced by dietary fat levels. The best growth performance was observed in fish fed 10% and 15% dietary fat. High dietary lipid levels led to higher fat deposition in whole fish, although lipid level in muscle remained low (1.1% in dorsal muscle and 1.7% in ventral muscle irrespective of diet). Significant subcutaneous fat accumulation was detected in turbot. No protein sparing effect by lipid was observed in turbot fed high dietary fat. Hepatic lipogenic enzymes (glucose-6-phosphate dehydrogenase, G6PD; malic enzyme, ME and acetyl CoA carboxylase) did not show any clear change in activity in response to dietary fat content. With regards to quality parameters, there were no differences in gutted and fillet yields among treatments. Sensory analyses of dorsal fillets indicated only a difference in exudation (corresponding to loss of water) and whiteness within treatments in accordance with instrumental colour analyses and on ventral fillets, only a difference of sweet flavour was observed. No differences in hardness were detected by either instrumental texture analysis or sensory analysis. In conclusion, although high dietary lipid levels affected growth and whole body composition of turbot adversely they induced very few alterations in flesh quality.

Fatty acid profile of fish following a change in dietary fatty acid source: model of fatty acid composition with a dilution hypothesis

Abstract The fatty acid (FA) content of fish is generally said to reflect fatty acid composition of the diet. In fact, incorporation of FA into tissues is modulated by various metabolic factors, and final composition will depend upon the initial FA content, cumulative intake of dietary fatty acids, growth rate and duration. Analysis of time course of changes in FA composition should be easier with animals having different initial FA profiles, which are subsequently fed a diet with the same FA composition. Data from two studies, one with brown trout and another with turbot were used. Fish were first fed with diets containing one of three different oils (soybean oil (SO), linseed oil (LO) and fish oil (FO)), and subsequently fed the same fish oil-based diet (washout period). If we suppose a model fish having the same initial composition as those fed vegetable oil and which incorporate fatty acid in the same way as the control fish always fed fish oil, we may compute a model of dilution of initial fatty acid content with increasing growth and absolute fat deposition. Experimental data can be compared with a reference fatty acid profile given by this model for the same fatty acid increase. Application of the model to experimental data shows that while muscle neutral lipid (NL) FAs roughly follow this dilution model, those of muscle polar lipids (PL) undergo much faster changes than model values based on increase of total polar lipid quantities. Among observed differences between the model and experimental values, DHA is of particular interest as this fatty acid displays lower change rates (significant in turbot neutral lipids) than expected in contrast to other fatty acids.

Ontogenic effects of early feeding of sea bass (Dicentrarchus labrax) larvae with a range of dietary n-3 highly unsaturated fatty acid levels on the functioning of polyunsaturated fatty acid desaturation pathways.

Four replicated groups of sea bass (Dicentrarchus labrax) larvae were fed diets containing an extra-high level of highly unsaturated fatty acids (HUFA) (XH; 3.7 % EPA+DHA), a high level of HUFA (HH; 1.7 %), a low level of HUFA (LH; 0.7 %) or an extra-low level of HUFA (XLH; 0.5 %) from day 6 to day 45 (experiment 1; XH1, HH1, LH1, XLH1). After a subsequent 1-month period feeding a commercial diet (2.7 % EPA+DHA), the capacity of the four initial groups to adapt to an n-3 HUFA-restricted diet (0.3 % EPA+DHA; R-groups: XH2R, HH2R, LH2R, XLH2R) was tested for 35 d. Larval dietary treatments had no effect on larval and juvenile survival rates. The wet weight of day 45 larvae was higher in XH1 and HH1 (P < 0.001), but the R-juvenile mass gains were similar in all treatments. Delta-6-desaturase (Delta6D) mRNA level was higher in LH1 and XLH1 at day 45 (P < 0.001), and higher in LH2R and XLH2R, with a significant increase at day 118.Concomitantly, PPARalpha and PPARbeta mRNA levels were higher in XLH1 at day 45, and PPARbeta and gamma mRNA levels were higher in XLH2R at day 118, suggesting possible involvement of PPAR in stimulation of Delta6D expression, when drastic dietary larval conditioning occurred. The low DHA content in the polar lipids (PL) of LH1 and XLH1 revealed an n-3-HUFA deficiency in these groups. Larval conditioning did not affect DHA content in the PL of R-juveniles. The present study showed (i) a persistent Delta6D mRNA enhancement in juveniles pre-conditioned with an n-3 HUFA-deficient larval diet, over the 1-month intermediate period, and (ii) brought new findings suggesting the involvement of PPAR in the Delta6D mRNA level stimulation. However, such nutritional conditioning had no significant effect on juvenile growth and lipid composition.

Microparticulate diets as first food for gilthead sea bream larva (Sparus aurata): study of fatty acid incorporation

Abstract Recent advances have led to the development of inert diets for first-feeding marine fish larvae. The purpose of the present study was to evaluate fatty acid (FA) incorporation into larva using practical-type and semipurified diets as first food for larvae. Experimental microparticulate diets were fed to gilthead sea bream larvae, right from the mouth opening to day 21 post hatching. Five basal diets were compared, using fish meal or casein as main protein sources, and fish protein concentrate or casein hydrolysates and algae powder ( Schizochytrium ). Diets contained soybean lecithin to provide polar lipids and this also provided a high linoleic acid (18:2n-6) content. n-3 HUFA (1.5–1.7% DM) were mainly in dietary neutral lipids, with a part in polar lipids in diets containing fish meal or fish hydrolysates. Fatty acid incorporation was studied by analysing FA content of larvae at the beginning and at the end of the trial. A semipurified diet (casein+ Schizochytrium powder) led to the best mean survival rate of 25% at day 21. While length increments were low, basal diets containing fish meal gave higher growth in size than casein-based diets. Whole body total fatty acid content differed between treatments and was higher in larvae fed casein-based diets than in those fed fish meal-based diets. As a result, fatty acid profiles shown showed various differences between treatments but not clearly related to dietary fatty acids. No clear sign of desaturation nor elongation of fatty acids was observed; the presence of 22:5n-6 (from Schizochytrium ) into some diets did not seem to induce retroconversion to 20:4n-6 by larva. Fatty acid profiles incorporated into larvae were compared to those of diets in order to display common tendencies: the incorporation of n-6 fatty acids was higher than their relative proportion in the diets, even for 18:2n-6 despite high dietary supply; incorporation of 20:4n-6 was two- to fourfold higher than the proportion in diets (irrespective of the level of 22:5n-6). Among saturated FA, high stearate but low myristate incorporation was observed. Taking into account the high level of n-3 HUFA in the larvae before first feeding, n-3 long-chain PUFA were not selectively incorporated into larvae during feeding, with a negative tendency for EPA, and variable incorporation of DHA between treatments.

Growth and survival of European sea bass /Dicentrarchus Labrax larvae fed from first feeding on compound diets containing medium-chain triacylglycerols

Abstract A 21-day feeding trial was carried out to investigate the ability of first feeding European sea bass larvae to utilize medium-chain triacylglycerols as an alternative source of energy. Three compound diets based on soluble fish protein concentrate and yeast were supplemented with either 3% tricaproin (TC6), tricaprylin (TC8) or tricaprin (TC10). A diet containing triolein (TOL) was used as a reference diet. Diets were tested on four replicate groups of first feeding European sea bass larvae at 20°C, i.e. 6 days after hatching. At the end of the 21-day trial, TC8 yielded significantly higher survival (57±8% vs. 28±11% for the three other groups). Considered together, larvae fed TC8 and TC6 displayed better growth rates than larvae fed TOL and TC10 (final mean wet weights: 1.5±0.3 mg vs. 1.2±0.2 mg, respectively). The fatty acid composition of larval total lipid revealed a low deposit of medium-chain fatty acids (between 1 and 3% of total fatty acids) suggesting that medium-chain fatty acids were oxidized for energetic purposes. Tricaprylin and to a lesser extent tricaproin, appear to be potential energy sources for first feeding European sea bass larvae reared on compound diets.

Commercial single-cell proteins either as sole food source or in formulated diets for intensive and continuous production of rotifers (Brachionus plicatilis)

Abstract Commercial Spirulina, Chlorella , and a methanol-grown yeast were tested as sole food source for the rotifer Brachionus plicatilis . Some good results were obtained, but only with medium salinity (18%) and none with seawater (35‰). In comparison with a constant supply of food, different adjustments of the food level to the population density were tested: a proportional and continuous or stepwise adjustment and a less proportional one. The less than proportional adjustment was found to be more advisable for a continuous culture with a daily renewal of a quarter of the volume. The three single-cell proteins appeared to be suitable with 35–55 rotifers produced per ml per day. However, the food conversion was poor: in the best cases 4.2 g of food were required per 10 6 rotifers produced. In practice, two formulated diets were preferred for mass culture trials in 60-l tanks: the first (P 72) included 40% Spirulina , 40% yeast and different additives; the second was composed of 67% of diet P72 and 33% of the freeze-dried alga Platymonas suecica . The production was 44 and 35 rotifers, respectively per ml per day, with 3.6 and 2.9 g of food, respectively per 10 6 rotifers,produced. Freeze-dried algae did not appear to be necesary for rotifer production, but the nutritional quality of such rotifers should be investigated.

The dietary value for sea-bass larvae (Dicentrarchus labrax) of the rotifer Brachionus plicatilis fed with or without a laboratory-cultured alga

Abstract Rotifers were fed on a laboratory-cultured alga, Platymonas (= Tetraselmis) suecica , and/or a diet composed of commercial single-cell proteins. They were given to sea-bass larvae up to day 15–20 after hatching, while Artemia nauplii were supplied from day 9–13. At day 21, the survival rate of fish obtained with rotifers fed on compound diet ranged between 32 and 82%, and their mean weight between 5.0 and 7.8 mg. When rotifers were fed either only on algae or on a mixture of 33% algae and 67% compound diet, the growth and survival rates of sea-bass were not clearly different to those obtained with rotifers fed on compound diet. No significant difference was observed when these rotifers were enriched with nutrients just before distributing them to fish. However, these rates appeared to be quite high in comparison to those obtained by several other authors. We can therefore recommend rotifers fed on compound diet as being, even without enrichment, convenient and low-cost food for sea-bass larvae.

Use of borage oil in rotifer production and Artemia enrichment: effect on growth and survival of turbot (Scophthalmus maximus) larvae

Abstract Three oils were used together with bakers yeast to enrich rotifers (long-term enrichment) and Artemia (24-h enrichment). These oils were: (A) cod liver oil, (B) an n −3HUFA concentrate, (C) a mixture (2:1) of the same n −3HUFA concentrate and borage oil. The n −3 concentrate (B) induced higher n −3HUFA content in rotifers and Artemia than the other oils. Borage oil supplied linoleic acid and γ -linolenic acid (18:3 n −6) in oil C. Rotifers fed oil C contained 2% 18:3 n −6 and 3% dihomo- γ -linolenic acid (20:3 n −6), but the arachidonic acid content was not different from the other treatments. No sign of elongation of 18:3 n −6 to 20:3 n −6 was observed in Artemia enriched with oil C. These live food organisms were compared as food for turbot larvae, at first feeding, growth of turbot larvae was lower when they were fed with the rotifers produced with oil B compared to the other treatments. Subsequently, when larvae were fed on enriched Artemia , the growth was influenced by larval density and dietary n −3HUFA. Treatment C gave the best results in terms of survival, with less variation within replicates than the other treatments. These results suggest that n −6 fatty acids and probably dihomo- γ -linolenic acid have a beneficial effect on survival of larvae during the critical early life stages.