Alterations in lipid metabolism and use of energy depots of gilthead sea bream (Sparus aurata) at low temperatures
Introduction
The culturing of gilthead sea bream has been vastly improved by optimizing farming conditions. Nevertheless, in northern areas of the Mediterranean Sea production of this valuable fish is subject to significant water temperature fluctuations throughout the year. During the cold season, food intake is drastically reduced and fish growth comes to a stop (Tort et al., 1998). In particularly cold periods, sea bream can develop a pathological condition known as ‘winter syndrome’ or ‘winter disease’ (Bovo et al., 1995, Doimi, 1996, Tort et al., 1998, Sarusic, 1999, Gallardo et al., 2003), resulting in grave economic losses. Symptomatic animals present histopathological changes (hepatomegalia, fatty livers, and distended digestive tracts), as well as physiological alterations (increased amino acidaemia, low plasma albumin levels, increased plasma ASAT activity) (Gallardo et al., 2003). Some of these symptoms have also been observed when sea bream are subjected to cold water temperatures such as 12 °C or 8 °C (Ibarz et al., 2003, Ibarz et al., 2005, Sala-Rabanal et al., 2003). This species stops feeding below 13 °C under experimental conditions (Sánchez et al., 1999, Ibarz et al., 2003), constituting a temperature-induced fasting. Water temperatures below 13 °C are not unusual along the northwest Mediterranean coasts during winter.
Few studies are available on fasting in gilthead sea bream and even fewer still on the simultaneous effects of low temperature and fasting. Sea bream fasted for three weeks at 14 °C exhibited losses in body and liver mass, in addition to lower stores of protein, lipids, and glycogen (Power et al., 2001). This rather typical response to fasting contrasts with the hepatomegalia and liver lipid deposition observed in sea bream following a fall in temperature (Ibarz et al., 2005), or as presented by winter-affected animals (Gallardo et al., 2003).
Understanding the effects of low water temperatures, with the simultaneous induced fasting, would provide important insight into how gilthead sea bream cultured in winter can exhibit a particular pathological condition without a specific agent. In fact, this is the aim of the present study: analysing the physiological alterations that sea bream undergo following three different temperature changes, based on an initial value of 16 °C; specifically, from 16 °C to 14 °C (food-deprived), 12 °C (threshold temperature where animals refuse feeding) and 8 °C. Lipids proved to be the stores most affected by cold or fasting. Therefore, both their tissue distribution and lipid fraction fatty acid profiles (polar and non-polar) were analysed after 7 and 20 days of temperature drop. In addition, the activities of several hepatic enzymes related to lipid metabolism were examined. This study also provides data on the capacity of sea bream to adapt to low water temperatures, as shown by increases in certain enzyme activities, as well as by changes in the fatty acid profiles of polar lipid fractions.
Section snippets
Animals and experimental conditions
Juvenile gilthead sea bream, obtained during the month of March from a local fish farm (Ametlla de Mar, Tarragona), were acclimated indoors over 15 days at 16 °C under a natural photoperiod (11.5:12.5 — Light:Dark, February). Thereafter, fish were randomly distributed, and adapted for three additional weeks, in three 600 l conical tanks (25 animals in each, at an approximate density of 3–4 kg·m− 3) connected to a semi-closed recirculating system, with biological and solid filters, an ozone
Body parameters and reserves
Gilthead sea bream cooled to 12 °C or 8 °C refused to feed, remaining in a temperature drop-induced fasting condition for the rest of the experimental period (20 days). Fish cooled to 14 °C did not receive any food over this same period. Both the 14 °C and 12 °C groups swam normally and did not exhibit any external sign of distress. Fish at 8 °C rested at the bottom of the tank, their movements comparatively sluggish, although their reactions to external stimuli appeared normal. Cold-induced
Discussion
Energy needs of ectotherms depend on the environmental temperature. Lupatsch et al. (2003) observed in gilthead sea bream, a direct relationship between daily energy requirements and water temperatures, but fish in this study were at temperatures higher than 18–19 °C. Confronted with a drop in temperature, this species behaves as a strict ectotherm (Ibarz et al., 2003) and, as we show in the present study, use their body stores according to the water temperature. Thus, fish at 14 °C suffered
Acknowledgements
The authors wish to thank Dr. M. Llobera and Dr. J. Peinado for their valuable suggestions on this manuscript. The assays of LPL and HL activities were determined in their Unitat de Lipids ([email protected]). We would also like to thank Dr. D. Furonés for providing the necessary facilities, and R. Carbó and M.A. Soubrier at the IRTA-Centre Aqüicultura for their technical assistance. This study was supported by grant CICYT-MAR97-0408-C02-0 from the Spanish government. M. Beltrán and A.
References (35)
- et al.
Isoproterenol increases active lipoprotein lipase in adipocyte medium and in rat plasma
Biochimie
(2003) - et al.
The role of polyunsaturated fatty acids in fish
Comp. Biochem. Physiol.
(1986) - et al.
Analyses of fatty acids from different lipids in liver and muscle of sea bass (Dicentrarchus labrax L.). Influence of temperature and fasting
Comp. Biochem. Physiol.
(1994) - et al.
A simple method for the isolation and purification of total lipids from animal tissues
J. Biol. Chem.
(1957) - et al.
Functional alterations associated with the ‘winter syndrome’ in gilthead sea bream (Sparus aurata)
Aquaculture
(2003) - et al.
Cold-induced alterations on proximate composition and fatty acid profiles of several tissues in gilthead sea bream (Sparus aurata)
Aquaculture
(2005) - et al.
Short- and long-term effects of refeeding on key enzyme activities in glycolysis–gluconeogenesis in the liver of gilthead seabream (Sparus aurata)
Aquaculture
(2003) - et al.
Fasting and Starvation
Lipid dynamics in fish: aspects of absorption, transportation, deposition and mobilization
Comp. Biochem. Physiol.
(1988)- et al.
Winter syndrome in the gilthead sea bream Sparus aurata. Immunological and histopathological features
Fish Shellfish Immunol
(1998)