F: Growth performance
Southwest U n i ve r s i t y, Chongqing, China. Channel catfish with an average initial weight of 50 g were held in 200 L fibreglass tanks. Fish in randomly assigned duplicate aquaria (40 fish per aquaria) were fed one of the two experimental diets to apparent satiation six times daily. Water temperature and pH were constant (23-24°C; pH 8.5) during the experimental period. Water flow was maintained at 4.5 L/minute. Orego-Stim® (50g kg-1) was a commercial product of Meriden Animal Health Ltd., UK. The dietary formulation of each of the diets was as follows: Control: without feed additives Orego-Stim®: 50g kg-1 Orego-Stim®
Experimental design and diets Both diets were formulated to be isocaloric (12.51kJ kg-1 diet) and isonitrogenous (3450g/kg-1 crude protein). All ingredients were finely ground, mixed in a Hobart mixer and pelleted through a 2.4mm diameter die in a Hobart meat grinder. The pellets were air-dried at room temperature, fragmented and stored in a freezer until use. Ingredients and proximate composition of the experimental diets are presented in Table 1. The feeding trial lasted eight weeks.
At each feeding, an excess amount of feed was fed to the fish and uneaten feed was collected one hour after feeding, dried at 70°C and reweighed. Leaching of uneaten feed was estimated by placing weighed samples of each diet into a tank without fish for one hour and then recovered, dried and reweighed. The average leaching value was used to correct the amount of uneaten feed.
Intestine bacteriological sampling Six channel catfish were sampled from each diet group after one-day starvation. The fish were killed by physical destruction of the brain, and the number of incidental organisms was reduced by washing the fish skin with 700 ml L-1 ethanol before opening the ventral surface with sterile scissors to expose the body cavity. The ventral belly surface of the fish was opened to expose the peritoneal cavity, and then the spleen, gallbladder and liver removed. The intestinal sections were emptied and thoroughly rinsed three times in 2ml sterile 9g/kg-1 saline to remove nonadherent bacteria. Anterior intestine (AI), mid intestine (MI), and posterior intestine (PI) of the corresponding sections were treated separately, and were then transferred to sterile plastic bags and homogenised in a Stomacher (Seward Laboratory, London, UK).
Bacterial plates spreading and count Homogenates of the intestinal sections were diluted in sterile 9g/kg-1 saline and appropriate dilutions were spread on the surface of fresh water agar (FWA) plates.
The formulating method of FWA as follows: MgSO4 (0.05g), beef extract (2.5g), NaCl (500g), K2HPO4 (0.2g), glucose (1g), peptone (5.0g), yeast extract (2.5g), agar powder (15.0g), add water to 1000 ml, pH 7.2-7.4, and was sterilised for 30 min at 121℃. 18 FWA plates were spread with homogenates of the intestinal sections in each group. Nine plates were incubated at 30℃ for 24-48 hours in an incubator, and nine plates were incubated at 30℃ for 48-72 hours in an anaerobic incubator. Plates with 20-200 bacterial colonies were counted and bacterial numbers in plates were converted to the number per unit weight of intestine.
Identification of bacteria Approximately 10 colonies were randomly picked from plates containing 20 to 200 bacteria. A total of 100 isolates were inoculated with a method of slope culture, respectively. 60 tubes were incubated at 30℃ for eight to 12 hours in an incubator, and placed at 4℃ after incubation. Another 40 tubes were incubated at 30℃ for 24 to 36h in an anaerobic incubator, and were identified after 4 hours. The identification process of aerobic bacteria was formulated according to Bergey’s Manual of Determinative Bacteriology and classified according to genera or groups on the basis of cell morphology, motility, gram reaction, catalase and oxidase and glucose fermentation, O/F test, salt tolerance for growth. Anaerobic bacteria were identified with an automatic microorganism identification instrument (VITEK-Ⅱ) by the French BioMerieux Company and identification plate (VITEK-ANA) for anaerobic bacteria.
Table 2: WG, SGR, FCR, PER and survival of Channel catfish fed different diets with feed additives
Diets
WG1 (g)
SGR2 (%/d)
FCR3
PER4
Survival
Control
102.63±2.22a
1.95±0.04a
1.94±0.092a
1.49±0.08a
95.83±2.89a
Car+Thy
116.77±2.49b
2.15±0.05b
1.84±0.03a
1.58±0.02a
95.00±2.50a
OS
127.53±6.40c
2.24±0.12b
1.64±0.04b
1.77±0.07b
98.33±1.44a
Data were presented as mean±SD (n=2). Value in the same column having different superscripts is significant (P<0.05). 1 WG (Weight gain, g) = final body weight − initial bodyweight 2 SGR (Specific growth ratio, ％/d) = (loge average final weight - loge average initial weight) / no days) x
100
3 FCR (Feed conversion ratio) = feed consumed (g, dry weight) / weight gain (g) 4 PER (Protein efficiency ratio) = weight gain (g) / protein intake (g)
32 | International AquaFeed | July-August 2010
Results - Growth performance Survival rate of the experiment was high (>95%) and unrelated to dietary treatment (see Table 2). Data on the growth performance of channel catfish, including weight gain (WG), specific growth ratio (SGR), feed conversion ratio (FCR) and protein efficiency ratio (PER) are shown in Table 2. WG of fish fed the OS diet was significantly higher than those of fish fed the Con diet (P<0.05). SGR of fish fed the OS diet