Monocultures of marine microalgae Isochrysis galbana and Tetraselmis suecica are often used as fodder for copepods, which are then fed to fish in recirculating aquatic systems. It has been shown that by feeding copepods on a mixed algal diet growth is often greater than when each of the species of the diet is fed individually. In our study the effects of different light intensities (10-200 μmol photons m-2 s-1) on growth performance and FA profile (with emphasis on polyunsaturated FAs) of the mixed culture of I. galbana and T. suecica, grown in batch cultures under laboratory conditions were compared with those in monoculture conditions. The maximum specific growth rates reached for I. galbana, T. suecica and mixed culture were 0,576 day-1 (80 μmol photons m-2 s-1), 1.008 (60/100 μmol photons m-2 s-1) and 0,216 day-1 (5 different light irradiances), respectively. The increase in growth rate of T. suecica along the increasing irradiances was more significant than that of I. galbana and the mixed culture which had the lowest growth rate of all three. Growth became light saturated at 60 μmol photons m-2 s-1 for I. galbana and T. suecica, whereas growth rate of mixed culture was almost stable after 20 μmol photons m-2 s-1. T. suecica grew more efficiently and seemed to suppress the natural growth of I. galbana in the mixed experiment with increasing light irradiance. T. suecica can be therefore considered as the dominant species. FA productivity was lowest in I. galbana at all light intensities. T. suecica yielded the highest FA productivity among the three cultures at 10, 20, 80 and 100 μmol photons m-2 s-1 and mixed culture at all other light irradiances. The greater docosahexaenoic acid (DHA) content was found in I. galbana, whereas T. suecica contained greater concentrations of αLinolenic acid (ALA), linoleic acid (LA) and eicosapentaenoic acid (EPA). The content of polyunsaturated FAs (PUFAs) essential to copepods were increasing with increasing light intensity for I. galbana and T. suecica (P-value<0,05). In the mixed culture DHA was abundant at low light intensities, whereas greater concentrations of ALA, LA and EPA were achieved above 60 μmol photons m-2 s-1 and simultaneously DHA was reduced to insignificant amounts. All in all, our conclusion is that it is better to grow monocultures of I. galbana and T. suecica at their most optimal growth conditions separately and use a mix of both as ideal feed for copepods instead of growing them in a mixed culture.
|Uddannelser||Miljøbiologi, (Bachelor/kandidatuddannelse) BachelorMiljøbiologi, (Bachelor/kandidatuddannelse) Bachelor el. kandidat|
|Udgivelsesdato||20 dec. 2016|
|Vejledere||Søren Laurentius Nielsen|