Irreversible starvation using RNA/DNA on lab-grown larval anchovy, Engraulis encrasicolus, and evaluating starvation in the field-caught larval cohort

The recruitment of anchovy Engraulis encrasicolus, the crucial forage fish in the Black Sea ecosystem, has drastically decreased in the last two decades, mainly due to overfishing. The wild-caught fertilized anchovy eggs were hatched and the larvae exposed to the different feeding levels to indicate the irreversible starvation criteria based on RNA/DNA, then the nutritional status of wild-caught larvae were evaluated. The newly hatched larvae had mean notochord length of 3.25 +/- 0.04 mm and first feeding started on day 3 after hatching. The feeding levels applied to produce the irreversible starvation were fed control (FC), unfed control (UC), delayed first feeding for 1 (1DF), 2 (2DF) and 3 days (3DF). The whole body RNA/DNA ratio and the daily protein growth rate were individually analyzed. There were no survivors left in unfed group on day 6. Irreversible starvation (IS) occurred on the first day after first feeding which suggest the Black Sea anchovy larvae have a very low tolerance to starvation and the critical RNA/DNA ratio was 1.022 +/- 0.20. The survival rate in the unfed control was similar to the other delayed groups. The highest daily protein growth rates were on day 6 with 43.45% for FC. Based on IS derived from RNA/DNA, 91% survival probability was detected in field-caught larvae. In future, irreversible RNA/DNA ratio can be used for monitoring and comparing of nutritional status and recruitment probability of different cohorts of the Black Sea anchovy larvae.