RNA-DNA ratio as physiological condition of rainbow trout fry fasted and fed

Abstract

Seventeen day old rainbow trout fry, Oncorbynchus mykiss, were subjected to four feeding regimes during 13 days at-10° C: continuously fasted; delayed fed after 6 days fasting; fed ad libitum with Trout Chow #3 three (at 08: 00, 12: 30 and 17: 00 h); or six (08: 00, 10: 00, 12: 00, 14: 00, 16: 00, and 18: 00 h) times a day. Total RNA and DNA concentrations of the fry were measured by fluorometry at two day intervals. Fed fry continuously grew from ∼ 99 mg to over 200 mg after 13 days, but starved fish underwent growth loss of-73 mg. Their condition factors (K) increased from ∼2.2 to ∼7–8 for the fed, and decreased to ∼1.9 for the fasted fish. Specific growth rate per day (SGR) increased from 0.05 mg to-33.6 mg for the continuously fed fry six times a day (average 9.8% per day) and 29.7 mg for the fry fed three times a day (8.5%), but-1.15 mg for the fasted fry (-1.96%). Fed fish starved for 6 days, recovered their SGR after three days following feeding (day-9), but did not catch up to the continuously fed fish (-0.73%). DNA concentrations increased from-450 μgmg per fish to-600 μgmg for the starved fish,-440 μg mg for the delayed fed, and-290 μg mg for the continuously fed fish. RNA concentrations were ∼466 μg-mg for the starved,-840 μgmg for the re-fed, and-960 μg. mg for the fed fry. RNA/DNA ratios changed from 1.72 to 0.73 for the starved, 1.96 to 1.91 for the delayed feeding, and 1.8 to 3–3 for the fed three times a day, and 1.8 to 3.4 for the fed six times a day after 13 days. No significant differences existed between the fish fed three and six times a day. The results confirmed that SGR, total weight increment, and K were all higher in fed fish than in starved, indicating that feeding has a great influence on RNA/DNA ratio as physiological index in rainbow trout fry. © 1998 Taylor & Francis Group, LLC.