Defining the starvation potential and the influence on RNA/DNA ratios in horse mackerel (Trachurus mediterraneus) larvae

Larval survival potentially affects recruitment strongly. Variability in larval growth rates, primarily caused by variable nutritional situations, is one of the factors that can influence larval survival rates. RNA/DNA ratio as well as protein content was analyzed in wild-caught laboratory-grown and in wild-caught horse mackerel Trachurus mediterraneus in relation to feeding and starvation. For this purpose, field-caught genoblast eggs were incubated and the hatched larvae were reared under different feeding regimes: fed control, unfed control, starved either for 1, 2 or 3 days, on feeding restrictions. The whole-body RNA/DNA ratio and the daily protein growth rate were individually analyzed. In all larvae eye pigmentation, mouth opening and subsequently first feeding started on the third day after hatching. All larvae in the unfed group died on day 8. The survival rate during the first 3 days in delayed feeding groups was higher than that of the unfed group. Overall, growth curves from feeding-delayed larvae indicated that fish fed after up to 3 days starvation were capable of complete recovery with the critical RNA/DNA ratio of 1.05 ± 0.08. According to this value, approximately 10 % of the field-caught larvae were starving. Therefore, the RNA/DNA ratio is an easy tool to assess the nutritional status in horse mackerel larvae caught in the field with a high precision rate.