As knowledge of larval nutrition progresses and newer technologies become available, better performing microdiets for fish will become available.
shows that both gilthead seabream and meagre larvae require a high protein/high lipid diet for an optimal performance. Diets with lower lipid contents (i.e. 15-17% crude fat), which are currently used in commercial hatcheries, may result in a lower growth in meagre. In gilthead seabream, this scenario may also occur unless a very high protein diet is used. Moreover, diets containing high lipid contents did not affect liver histology or skeletal development in both species. Also revealing how microdiet formulations still show room for improvement, a trial conducted with Senegalese sole larvae showed that dietary phosphorous levels can have a strong impact on larval development. In this scenario, high phosphorous levels led to a depression of larval growth, whereas optimal levels increased larval growth (ranging from 4.4 to 6.4 % day -1) and survival (from 60 to 81 %). In addition, optimal phosphorous levels also led to an increased vertebral bone density (Figure 3) and vertebral growth (Figure 4).
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Fig. 3. Analysis of vertebral bone density by X-ray microradiograph. A higher pixel frequency, indicating a higher density of bone, is observed in sole fed a diet containing an optimal phosphorus levels.
Fig. 4. Analysis of vertebral growth by double staining with Alizarin Red S and Calcein. Vertebral growth is assessed by analysing the bone formation between first (Calcein) and second (Alizarin) stainings.