Inclusion of macroalgae meal (Macrocystis pyrifera) as feed ingredient for rainbow trout (Oncorhynchus mykiss): Effect on flesh fatty acid composition

The e¡ect of dietary inclusion of whole grain white lupin (Lupinus albus) on growth performance, histology, muscle fatty acid composition and nutrient digestibility was investigated in an 11-week growth and a 4-week digestibility trial with rainbow trout (initial body weight of 54.0 AE 6.2 and 181.9 AE 3.4 g respectively). Four experimental extruded diets were formulated to contain 0%, 30%, 40% and 50% of whole grain lupin and fed to triplicate groups of ¢sh twice a day until apparent satiation. Faeces were collected daily from each digestibility tank by decantation. No signi¢cant trends were observed with respect to growth, feed utilization, apparent digestibility coe⁄cients or whole-body composition (P40.05). Conversely, increasing levels of dietary lupin led to signi¢cant decreases in the Hepatosomatic index (R 2 50.75, Po0.05) and slight lipid in¢ltration into hepatocytes and enterocytes. Muscle fatty acid compositions were slightly a¡ected by the dietary treatment. Polynomial regression of dietary inclusion of lupin and muscle fatty acid concentrations showed an increase in C18:1n-9, C18:2n-6 and C18:3n-3 and a decrease in C20:5n-3 with increasing dietary lupin level. These results demonstrated that whole grain lupin can be included up to 50% in commercial rainbow trout diets without negative e¡ects.

Galaxias maculatus eggs and larvae obtained from broodfish captured either in an estuarine or a freshwater environment, as well as from cultured broodstock were analysed to compare their lipid and fatty acid profiles. Results showed a lower lipid content in embryos and larvae from estuarine populations than those from fresh water, denoting the influence of environmental conditions. The n-3:n-6 ratio was higher in eggs from estuarine and cultured populations, being in the range of marine fishes, whereas for eggs from freshwater fish was lower and typical of freshwater fishes. The polyunsaturated fatty acids (PUFA), particularly docosahexaenoic acid (22:6n-3) and eicosapentaenoic acid (20:5n-3), were higher in eggs and larvae of broodstock coming from culture or estuarine environments than in those from fresh water. Moreover, these fatty acids markedly increased after hatching in larvae coming from estuarine populations, suggesting the effect of the environment on fatty acid profiles to physiologically prepare the larvae to adapt to higher salinity conditions. Linoleic acid (18:2n-6) content was higher in fresh water fish and its reduction during embryo and larval development was accompanied by a significant increase of arachidonic acid (20:4n-6), which was not observed in embryos or larvae from broodstock fish from estuary or aquaculture origin. Both environment and diet of broodstock fish affected lipid and fatty acid composition of G. maculatus embryo and larvae as well as their changes during development.

Evidence is presented that Philometra sp. infects Paralabrax humeralis only after first maturity