Stable carbon (δ13C) and nitrogen (δ15N) isotopes as natural indicators of live and dry food in Piaractus mesopotamicus (Holmberg, 1887) larval tissue

This study proposed the use of the stable isotope technique to track the type of food utilized by pacu Piaractus mesopotamicus larvae during their development, and to identify the moment when the larvae start using nutrients from the dry diet by retaining its carbon and nitrogen atoms in their body tissues. Five‐day‐old pacu larvae at the onset of exogenous feeding were fed Artemia nauplii or formulated diet exclusively; nauplii+formulated diet during the entire period; or were weaned from nauplii to a dry diet after 3, 6 or 12 days after the first feeding. δ¹³C and δ¹⁵N values for Artemia nauplii were ?15.1‰ and 4.7‰, respectively, and ?25.0‰ and 7.4‰ for the dry diet. The initial isotopic composition of the larval tissue was ?20.2‰ and 9.5‰ for δ¹³C and δ¹⁵N respectively. Later, at the end of a 42‐day feeding period, larvae fed Artemia nauplii alone reached values of ?12.7‰ and 7.0‰ for δ¹³C and δ¹⁵N respectively. Larvae that received the formulated diet alone showed values of ?22.7‰ for δ¹³C and 9.6‰ for δ¹⁵N. The stable isotope technique was precise, and the time at which the larvae utilized Artemia nauplii, and later dry diet as a food source could be clearly defined.     

Consumption of feeds containing the antibiotic sulfadiazine by gilthead sea bream (Sparus aurata,L.) and rainbow trout (Onchorynchus mykiss,Walbaum)

A method for studying the efficacy of sulfadiazine as a marker to estimate feed intake is presented. Feeding studies were carried out with two species, rainbow trout as a freshwater fish model and gilthead sea bream as a marine fish model, using two temperatures and two sizes of juveniles. The study showed the different feeding behaviour observed in both species, depending on the temperature and the number of days feeding the particles with sulfadiazine, and confirmed a dominant‐subordinate behaviour especially in the case of gilthead sea bream juveniles.     

The in vivo incorporation and metabolism of [1-14C] linolenate (18:3n-3) in liver, brain and eyes of juveniles of rainbow trout Oncorhynchus mykiss L and gilthead sea bream Sparus aurata L.

Accumulation of docosahexaenoic acid (DHA; 22:6n-3) in brain and eyes during development has been demonstrated in fish but it is not clear whether liver or neural tissues themselves are of greater importance in the biosynthesis of DHA from dietary 18:3n-3. In the present study, we investigated the in vivo metabolism of intraperitoneally injected [1-¹⁴C]18:3n-3 in liver, brains and eyes of young juvenile fish. Metabolism was followed over a 48h time-course in order to obtain dynamic information that could aid the elucidation of the roles of the different tissues in the biosynthesis and provision of DHA from dietary 18:3n-3. The study was performed in both a freshwater fish, rainbow trout Oncorhynchus mykiss L and a marine fish, gilthead sea bream Sparus aurata L to determine the effect that low or limiting5-desaturase activity may have in this process. As expected, the results showed that although the sea bream incorporated more 18:3n-3 into its lipids, metabolism of the incorporated fatty acid by de saturation and elongation was generally greater in the trout. In liver, the percentages of radioactivity recovered in tetraene and pentaene products were greater in trout than in sea bream although there was no difference in hexaenes. In contrast, the re covery of radioactivity in DHA was significantly greater in brain in trout compared to sea bream. In both species, the percentage of radioactivity recovered in desaturated/elongated products was much lower in liver than in brains and eyes, but that percentage increased over the 48h time-course. In trout though, the highest percentages of desaturated products in brain and eye were observed after 12 and 24h, respectively. However in sea bream the highest percentages of desaturated products in the neural tissues were observed after 24-48h. Radioactivity was recovered in 24:5n-3 and 24:6n-3, intermediates in the 4-independent ("Sprecher shunt") pathway for the synthesis of DHA, in both species, especially in the brain and eyes. Overall, although the results cannot eliminate a role for liver in the biosynthesis and provision of DHA for developing neural tissues in fish, they suggest that DHA can be synthesised in fish brain and eye in vivo.