DIFFERENT SOURCES AND LEVELS OF DIETARY PHOSPHOLIPIDS IN LOW FISH MEAL BASED DIETS FOR SEA BREAM (SPARUS AURATA)
Introduction
Plant meals are good alternatives to fish meal when used in aqua feeds for a big number of cultured fish (Nengas et al., 1996; Refstie et al., 2001; Kaushik et al., 2004) including sea bream (Benedito Palos et al. 2007). Phospholipids and their role in fish nutrition have been recently reviewed by Tocher et al. (2008). Growth improvement in larvae and juvenile fish, increased survival and decreased incidences of malformation and even increase in stress resistance are some of the beneficial effects of dietary phospholipids. The total content of phospholipids as well as the phospholipids profile may vary between different types of fish meals and plant meals (Sargent et al., 2002). Therefore, substituting fish meal with plant alternatives may affect the dietary phospholipids levels highlighting the importance of meeting fish requirements for these nutrients. However, only few studies have focused on phospholipids requirements of fish, namely in larvae of pikeperch (Hamza et al., 2011), sea bream (Saleh et al., 2012a; Saleh et al., 2012b) and juvenile fish of cobia (Trushenski et al., 2011). Therefore, the objectives of the present study was to investigate the effects of two different sources of phospholipids at three different dietary levels on growth performance, feed utilization, liver histology, and fatty acid profile of polar and neutral lipids of liver, muscle and intestine of sea bream.
Materials and Methods
Juvenile sea bream (Sparus aurata) (initial weight 12.05 ± 0.41g) kept in triplicate tanks were fed 8 experimental diets differing in the source and level of phospholipids. A high-FM (62% FM, FM) diet was used as a positive control, and a low-FM diet (10%, KS0 diet) as a negative one. Two different sources of phospholipids (marine-krill oil; K) and (vegetable-soya lecithin; S) were added to the low FM diet at 3 inclusion levels, namely 0.5%, 1% and 2% for K1-S1, K2-S2, K3-S3 diets, respectively. All diets were isonitrogenous and isolipidic with 48% protein and 18% fat. Diets were fed to the fish ad libitum in two meals/day for 10 weeks at water temperature 25.2±10C. At the end of the trial fish were individually weighed for growth parameters determination. Samples were taken for analyses of whole body composition, fatty acids profile and histological examination.
Results
Growth performance as SGR of the fish was affected positively by phospholipids inclusion level compared to the KS0 diet even at the lowest inclusion level. Phospholipids sources showed little difference amongst them, with marine showing a trend of being more effective than soya lecithin at low levels although the difference was not significant. The supplementation of phospholipids resulted in decreased FCR although differences were not significant. Neither body composition nor liver fat content was affected by phospholipid source and inclusion level. Histological observations of liver tissue showed lipid accumulation with a simultaneous peripheral nuclei translocation in Diets KS0, K1, S1 while in the rest of the diets hepatocytes had a similar morphology, with central located nuclei and regular size of hepatocytes.
Differences in fatty acid profile of neutral and polar lipids from liver, muscle and intestine between different dietary treatments were correlated to dietary fatty acids.
Discussion-Conclusion
In the present study, the inclusion of 0.5% phospholipids of either marine or plant origin in low FM diets resulted in growth improvement and feed utilization comparable to those of FM control, while inclusion of 1% of phospholipids further improved liver histology. Higher phospholipids requirement (2-4%) of diet is reported in literature for juvenile fish (Tocher et al., 2008) while in cobia 1% of marine origin phospholipids is reported by Trushenski 2011. Phospholipids are known to facilitate digestion and absorption of lipids and other nutrients, while consisting fundamental constituents of cell membranes (Tocher et al. 2008). The efficacy of their action can be attributed to the different classes of phospholipids depending on the different sources. The determination of phospholipids classes will enable us to explain differences between levels and sources of phospholipids.
References
Benedito-Palos, L., Saera-Vila, A., Calduch-Giner, J-A., Kaushik, S.J., Pérez-Sánchez, J., 2007. Combined replacement of fish meal and oil in practical diets for fast growing juveniles of gilthead sea bream (Sparus aurata L): networking of systemic and local components of GH/IGF axis. Aquaculture 267, 1-4, 199-212.
Kaushik, S.J., Cove`s, D., Dutto, G., Blanc, D., 2004. Almost total replacement of fish meal by plant protein sources in the diet of a marine teleost, the European seabass, Dicentrarchus labrax Aquaculture 230, 391-404
Nengas, I., Alexis, M.N., Davies, S.J., 1996. Partial substitution of fishmeal with soybean meal products and derivatives in diets for the gilthead sea bream (Sparus aurata L.). Aquaculture Research 27, 147-156
Robaina, L., Izquierdo, M., 2012. Potential of three krill products for seabream larval production. Aquaculture Research 43, 395-406.
Refstie, S., Storebakken, T., Baeverfjord, G., Roem, A.J., 2001. Long-term protein and lipid growth of Atlantic salmon (Salmo salar) fed diets with partial replacement of fish meal by soybean products at medium or high lipid level. Aquaculture 193, 91-106.
Saleh, R., Betancor, M.B., Roo, J., Benitez-Santana, T., Hernandez-Cruz, C.M., Moyano, F-J., Izquirdo, M., 2012a. Optimum krill phospholopids content in microdiets for gilthead seabream (Sparus aurata) larvae. Aquaculture Nutrition 19, 449-460.
Saleh, R., Betancor, M.B., Roo, J., Benitez-Santana, T., Hernandez-Cruz, C.M., Moyano, F-J., Izquirdo, M., 2012b. Optimum soybean lecithin contents in microdiets for gilthead seabream (Sparus aurata) larvae. Aquaculture Nutrition 19, 585-597.
Trushenski, J., Schwarz, M., Pessoa, W.V.N., Mulligan, B., Crouse, C., Gause, B., Yamamoto, F., Delbos, B., 2011. Amending recuced fish-meal feeds with marine lecithin, but not soy lecithin, imroves the growth of juvenile cobia and may attenuate heightened responses to stress challenge. Animal Physiology & Animal Nutrition DOI:10.1111/j.1439-0396.2011.01255.x
Sargent, J.R., Tocher, D.R., Bell, J.G., 2002. The lipids, In: Halver, J.E., Hardy, R.W. (Eds.), Fish Nutrition, 3rd ed. Academic Press, San Diego, pp. 181-257.
