A. Hagiwara, W.G. Gallardo, A. Belem de Araujo, A. Hosoe, T.W. Snell
Abstract:
Reliable tools to rapidly assess the physiological condition of cultured rotifers have been scarce. The activity of certain rotifer enzymes can be determined in vivo with substrates that have been used in ecotoxicology. These substrates are non-fluorescent but are cleaved by endogenous enzymes to yield fluorescent products. Neonates of Brachionus plicatilis hatched from cysts were exposed to media with series of free ammonia (control and 2.2-37.6 ppm) and increasing viscosity (relative viscosity against filtered seawater = 1-1.169) regulated by the addition of methyl cellulose. Fluorescence intensities of glucosidase and esterase decreased with increasing free ammonia and viscosity, respectively. There was a significant correlation of enzyme activities with rotifer life span and fecundity at 25 C on a diet of Nannochloropsis oculata. In vivo enzyme activity is therefore useful for diagnosing stress in individual rotifers. The growth of rotifer mass cultures can be manipulated by the addition of particular vertebrate hormones or neurotransmitters.
From batch culture trials in 50 mL, we found that the addition of growth hormone (0.0025 and 0.025 IU/mL) or gamma-aminobutyric acid (GABA, 50 ppm) significantly increased the rotifer population growth 1.7 and 2 fold, respectively, as compared to controls. From individual culture experiments in 1 mL media, the addition of GH or GABA to rotifer cultures was effective even when rotifers were exposed to high free ammonia concentration (7.5-9.7 ppm) or low food levels (Nannochloropsis oculata, 7x10^5 cells/mL).
(Faculty of Fisheries, Nagasaki University, Nagasaki 852-8131, Japan)