Search

The effects of three medicinal plants in the feeds of juvenile Nile tilapia (Oreochromis niloticus) were investigated on growth, survival, immunity, and digestive histology at various inclusion levels: (A) Guiera senegalensis at 0, 1, 2, 4, and 8%; (B) Pluchea odorata at 0, 0.5, 1, 2, and 4%; (C) Piliostigma reticulatum at 0, 1, and 2%; and (D) a mixture of the three at 0, 1, and 2%. After 28 days of feeding, fish were infected with Aeromonas hydrophila for 12 days. The results showed that, except for G. senegalensis, the inclusion of the medicinal plants, alone or combined, enhanced the immune response. The diet with 4% P. odorata significantly increased plasma lysozyme and bactericidal activities without affecting feed conversion efficiency or growth. Despite improved immunity, none of the treatments enhanced post-infection survival rates. However, fish fed the 1% mixture showed healthier livers and intestines, with reduced cell swelling and normal lipid deposits, followed by the 2% mixture and the control. These results highlight the potential benefits of incorporating P. odorata and the plant mixture into the diets of Nile tilapia juveniles for enhancing their immune response against A. hydrophila. [ABSTRACT FROM AUTHOR]

Accurately measuring the phenotype at the individual level is critical to the success of selective breeding programs. Feed efficiency is a key sustainability trait and is typically approached through feed conversion ratio (FCR). This requires measurements of body weight gain (BWG) and feed intake (FI), the latter being technically challenging in fish. We assessed two of the principal methods for measuring feed intake in fish over consecutive days: (1) group rearing 10 fish per group and video recording the meals and (2) rearing fish individually on a restricted ration. Juvenile Nile tilapia (Oreochromis niloticus) from the Genetically Improved Farmed Tilapia (GIFT) strain and the Cirad strain were entered into the study (128 GIFT and 109 Cirad). The GIFT strain were reared over three consecutive periods of 7 days each under different feeding, recording, and rearing scenarios (i) in groups fed an optimal ration (g100) or (ii) fed a 50% restricted ration (g50) both with video records of all meals and (iii) reared in isolation and fed a 50% restrictive ration. The Cirad strain were tested similarly but only for scenarios (i) and (iii). All fish were fed twice daily with a calculated ration. Correlations showed the same trends for the GIFT and the Cirad strains. For the GIFT strain, correlations were positive and significant for BWG and FI measured in scenarios (i) and (ii), 0.49 and 0.63, respectively, and FI measured in scenarios (i) and (iii) (0.50) but not for BWG measured in scenarios (i) and (iii) (0.29, NS). The phenotypic correlation estimated for FCR between scenarios (i) and (ii) with fish fed an optimal or a 50% restricted ration was low and not significant (0.22). Feed Conversion Ratio for GIFT fish reared in groups or in isolation and fed with a restricted ration [scenarios (ii) and (iii)] were not significantly correlated either. Social interactions between fish, potentially impacting their efficiency, may explain the results. Therefore, selective breeding programs seeking to improve feed efficiency will need to carefully plan the feeding rate and the rearing system used to estimate FCR in order to optimize selection for the targeted production system. [ABSTRACT FROM AUTHOR]

Individual identification of fish is often desirable for the smallest possible size, but it is crucial that tagging does not interfere with fish survival, physiology, or behavior. We evaluated radio-frequency identification (RFID) tags (10 mg) and PIT tags (PIT; 32 mg) in fish of two different size-classes of Nile TilapiaOreochromis niloticus: 200–500 mg and 640–1,600 mg, wet mass (WM). This produced four categories of tag load for each type of tag: 5.0, 3.3, 2.5, and 2.0% of WM. We tested 30 fish per category. Survival averaged 95.8% for RFID tags and 98.3% for PIT tags. Tag retention after 35 d was 99.1% for RFID tags and 96.6% for PIT tags. Tagged fish grew more slowly than controls. Growth penalty was proportional to tag load, but restricted to the first 4 d after tagging and compensated by catch-up growth, except in fish <300 mg presumably due to greater difficulties of handling and tagging. Small PIT tags can thus be used confidently in tilapia of about 1.3 g and RFID tags in tilapia of about 0.4 g. If growth is not a premium, the corresponding minimal sizes are 1.0 (for PIT) and 0.3 g (for RFID). Received February 11, 2014; accepted March 30, 2014 [ABSTRACT FROM PUBLISHER]