The current study examined the combined effects of feeding rates and feeding types on the water quality, growth
performance, digestive enzymes, blood parameters, and liver antioxidant enzymes of Nile tilapia (Oreochromis
niloticus) fingerlings reared under a biofloc system. A 3 × 2 factorial experimental design was used with three
feeding rates (2%, 3%, and 4%) and two feeding types (sinking or floating feed), comprising six treatments with
three replicates. Fingerlings with an initial body weight of 4.50 ± 0.25 g were stocked in eighteen circular plastic
tanks (0.5 m3) at a stocking density of 35 fish per tank fed three times a day at 10:00, 12:00 and 15:00. Starch
was added to all treatments as an organic carbon source at a C/N ratio of 10:1. The phytoplankton community
was determined to consist of twenty-two species, including individuals from the classes Cyanobacteria, Chlorophyceae, and Bacillariophyta. The most common phytoplankton classes were Chlorophyceae, followed by
Cyanobacteria, and fish-fed floating feed at a feeding rate of 2% of total biomass yielded the greatest number of
phytoplankton communities. Eight zooplankton species belonging to rotifers and protozoa were identified during
this experiment. The highest values of final body weight, weight gain, and specific growth rate were recorded for
a fish-fed floating diet with the highest feeding rate (4% of biomass). The highest hepatosomatic index (HIS) was
detected in a fish-fed floating diet at a rate of 4% of total biomass. Though fish-fed sinking feed with a 4%
biomass feeding rate presented the highest spleen index (SI). The highest significant (P < 0.05) level of amylase
was found in fish-fed sinking feed at a 4% feeding rate. While lipase activity was higher (P < 0.05) in the group
fed floating feed at a feeding rate of 3% of total biomass. Feeding rates, feed types, and their interactions had no
appreciable effect (P > 0.05) on hemoglobin (Hb), hematocrit (Hct), and red blood cells (RBCs). Feeding rate,
feed type, and their interactions had no significant impact (P > 0.05) on serum alanine aminotransferase (ALT),
aspartate aminotransferase (AST), or albumin, but feeding rates or feed types had an effect (P < 0.05) on total
protein and globulin (P < 0.05). The highest levels of growth hormone (GH) (P < 0.05) were found in fish-fed
either sinking feed at a feeding rate of 2% or floated feed at a feeding rate of 3% of total biomass. The fish group
fed floating or sinking feed at a feeding rate of 2%, floating feed at 3%, and sinking feed at 4% recorded the
highest high-density lipoprotein (HDL-C) values with an insignificant difference. Considering the liver’s antioxidant enzymes, the highest catalase (CAT) and glutathione (GSH) levels were shown in fish that received either
sinking or floating feed at feeding rates of 2% and 3%, respectively. Whereas, the lowest melanodialdehyde
(MDA) was found in fish-fed sinking feed at a feeding rate of 3% of total biomass. According to the study’s
findings, the biofloc system significantly improved both the water quality and the efficiency of Nile tilapia. In
addition, feeding tilapia 4% floating feed resulted in maximum feed consumption with minimal waste, improved
nutritional efficiency and feed conversion efficiency, lowered production costs, and lessened water pollution. |
