Abstract:
Emergence of antibiotic-resistant bacteria in fish is of public health concern. Assessment
of the suitability and safety of medicinal plants as alternatives to antibiotics in aquaculture
is imperative. However, there is limited information on the use of Allium sativum,
Chromolaena odorata and Talinum triangulare as feed additives due to their antimicrobial
potentials. This study was designed to investigate the use of these plants as feed additives,
and their antibacterial effects on Pseudomonas aeruginosa infection in Clarias gariepinus
(African catfish).
African catfish fingerlings (n=360, 1.10±0.01g) and juveniles (n=210, 117.30±1.57 g) were
randomised into 10 groups each and fed for 70 and 42 days, respectively. Formulated rations
containing three concentrations (A=0.5%, B=1.0%, and C=3.0%) of different treatments:
A. sativum (T1A, TIB, T1C), C. odorata (T2A, T2B, T2C), T. triangulare (T3A, T3B, T3C)
and control (no additive, CC) were fed to fish at 5% body weight. Growth parameters of
the fingerlings were monitored, while haematology and histopathology of gills, liver,
kidney and intestine of the juveniles were carried out. In vitro antibacterial effects of 25.0,
50.0 and 100.0% aqueous extracts (60g of the chopped dried leaves extracted with 300mL
of distilled water) of the plants against Pseudomonas aeruginosa were determined. Catfish
fingerlings (n=150; 53.1±0.23g) randomised into four groups were fed with pre-tested
effective rations T1A, T2B, T3B and CC. All fish were inoculated with Pseudomonas
aeruginosa (0.2 mL culture containing 1.4 x106
cfu/mL) intraperitoneally and their
survivability was evaluated by using mortality rate. Twenty four catfish juveniles
(146.4±0.74g) divided into four paired sub-groups: Q1 and Q2, Q3 and Q4, Q5 and Q6,
Q7 and Q8 were fed rations CC, T1A, T2B and T3B, respectively. Sterile incision of 45.0
mm by 1.0 mm was created on the dorso-lateral part of each fish and sub-groups Q2, Q4,
Q6 and Q8 were inoculated with Pseudomonas aeruginosa, while Q1, Q3, Q5 and Q7 were
not inoculated. Percentage healing rates were measured on days 3, 6, 9, 12 and 15 post incision. Data were analysed using descriptive statistics and ANOVA at α0.05.
Catfish on T3B and TIB had the least (4.70±0.11) and highest (6.32±1.01) feed conversion
ratios, respectively. Values for red blood cell, packed cell volume, haemoglobin
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concentration, mean corpuscular volume, mean corpuscular haemoglobin, mean
corpuscular haemoglobin concentration, lymphocytes and neutrophils were within normal
limits across the groups. No lesions were observed in fish fed with T1A and T3B; however,
other groups had mild gill lamellae hyperplasia and hepatic necrosis. The highest
antibacterial effect (inhibitory zone 12.50±1.26 mm) was recorded in 100% aqueous extract
of C. odorata. In the challenged groups, survival rates of 20% and 80% were obtained for
CC and T2B, respectively. At day 15 post-incision, T3B had significantly highest healing
rate in inoculated (86.7%) and uninoculated (100%) fish, with CC being 0.0% and 64.4%,
respectively.
The plants were established as growth promoters with antibacterial effects against
Pseudomonas aeruginosa infection in Clarias gariepinus. Inclusion rates at 1.0% of
Talinum triangulare or Chromolaena odorata is recommended to enhance growth, survival
and wound healing in Clarias gariepinus.
