International Journal of Aquaculture, 2024, Vol.14, No.1, 9-19 http://www.aquapublisher.com/index.php/ija 15 distribution and also keep the algae in constant circulation, continuous aeration through perforated air stones was provided. The micro-algae were raised on a combination of Diammonium phosphate (DAP) (15 g/L) and Urea (15 g/L) dissolved in 1.0 liter of de-chlorinated tap water. Algal culture conditions for the laboratory were maintained; temperature (25 ± 1.5) °C and pH were maintained at a range similar to that of the collection source (6.5 ~ 8.0). The cultures were also supplied with 24-hour constant lighting using a single 40 W (daylight) fluorescent tube (equivalent to 1 000 Lux). Counts of cells/mL were taken using a magnification of x200 on a Hund Wilovert Standard pH 20 inverted microscope (WILOVERT® series) and a Sedgwick-Rafter Cell counting chamber.The feeders allowed for an increase in the number of daily meals and for the extension of the feeding time throughout the day, but the rations must be fixed by the farmer, except when a demand feeder is used, as shrimp can then regulate their feed intake. Jescovitch et al. (2018) and Ullman et al. (2019b) reported a higher feed input with the sound feeder than manual feeding (181% and 171%, respectively), but feed input with the time feeder with respect to manual feeding was lower (112% and 118%, respectively), which could explain the high growth with an optimal FCR observed in sound feeding. In the study of Reis et al. (2020) the increment of 60% rations using a time feeder improved the yield, but it was lower than yield using sound feeder, due probably to feed input being higher with sound feeder, around 1 100 kg/ha more. 3.2 Copepod culture and estimation of survival Mass cultures of freshwater Thermocyclop sp. in the laboratory were maintained on a diet of freshwater microalgae (Chlorella sp.) as adopted from Chepkwemoi et al. (2013). The initial stock of the live Thermocyclop sp. was sourced from the Umoja fish farm (0°24'59" N, 32°23'00" E) and then acclimatized to the laboratory conditions; room temperatures, and continuous lighting. In the laboratory, the Thermocyclop sp. were screened to isolate the size fraction containing predominantly adult cyclopoids and later-stage copepodites; this was achieved by coarse screening through 45, 100 and 200 μm mesh size planktons. Finally, uncontaminated cultures of Thermocyclop sp. were achieved using sucker pipettes (Huawei® PIPETTE H100) of 10~30-micron (µ) aperture, coupled with a Hund Wilovert Standard pH 20 inverted microscope (WILOVERT® series) set at a magnification of x40 to pick out adult individuals. The collected samples were thereafter placed in a 100 mL Erlenmeyer flask, where Chlorella sp. was introduced. The uncontaminated Thermocyclop sp. was used as a stock culture by introducing 10~15 Thermocyclop sp. per mL in 10 L algae (Chlorella sp.) at a density (18.43±6.0)×104 cells/mL obtained by day 14 of the algae culture. Laboratory culture conditions for the copepods were maintained at the recommended levels. 40-watt electric lighting tubes were used for illumination. Constraints due to culture density were monitored to avoid decreased fecundity due to overcrowding; by upscaling when the density reached 10 individuals/L. The density of Thermocyclop sp. (individuals/L) was determined at a magnification of x100 using a Hund Wilovert Standard pH 20 inverted microscope (WILOVERT® series) on a Sedgwick-Rafter Cell counting chamber to guide the packaging densities utilized in this study. 3.3 Experimental setup Two sets of experiments (1 and 2) were run in series using the experimental facilities at the Department of Botany, Makerere University (0°20'09" N, 32° 33'56" E) with requisite storage conditions. Experiment 1 focused on determining the effect of packaging density on the survival of the Thermocyclop sp. at a fixed temperature (12 °C). The experiment comprised a total of 42 one-liter glass jars for each storage density (N=42). The storage densities were varied at 1000, 3000, and 5000 individuals/L, and the glass jars were placed in refrigerators set at 12 °C at the Department of Botany, Makerere University. The density variations were chosen based on previous studies and species characteristics, which indicated that copepods can survive for at least 20 days at a density of 500 individuals per liter and recommended that under controlled conditions, the stocking density can be increased (Drillet et al., 2015; Franco et al., 2017; Punnarak et al., 2017). Micro-algae (18.43±6.0×104 cells/mL) with dissolved Oxygen levels (4.0±1.0 mg/L) were added to each storage bottle and sealed. The three treatments were replicated in a Complete Block Design and the experiment was run for 14 days. To monitor survival, three one-liter jars of each treatment were enumerated daily (9 total daily) to establish the percentage of live or dead copepods in the bottle.
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