Mahmoud Rezk

Selection response for body weight at marketable size was measured for channel catfish, Ictalurus punctatus, grown in earthen ponds at 7500 fish/ha. Three generations of mass selection for increased body weight in Kansas and Marion strains of channel catfish increased body weight from 453 to 583 g or 29%, and from 530 to 642 g or 21%, respectively, with cumulative realized heritabilities of 0.17±0.016 and 0.19±0.012, respectively. Realized heritabilities for the third generation alone were 0.16±0.016 and 0.23±0.015 for Kansas and Marion strains, respectively. The results indicate that body weight can be significantly increased via mass selection in channel catfish, which should result in increased production and profitability in the catfish farming industry.

This study presents results of two generations of selection (G1 and G2) for growth of Nile tilapia. The selection environment consisted of earthen ponds which were fertilized daily with 50 kg dry matter (dm)/ha chicken manure. No supplementary feeds were provided. In total, 6429 fully pedigreed experimental fish were included in the analysis. Survival till harvest was highly variable ranging from 35% to 77% and was affected by initial weight, pond, and age effects. Body weight at harvest (BW) increased from a mean of 67.4 g in the grandparental (unselected) population (G0) to 129.5 g in G2 was affected by initial weight, pond, sex and age effects. Generations were discrete and therefore genetic parameters were estimated separately for each year. Heritability estimates for BW ranged from 0.38 to 0.60, and the heritability for survival ranged from 0.03 to 0.14. The estimated selection response was 23.4 g (34.7%) between G0 and G1 and 13.0 g (14.9%) between G1 and G2. These results demonstrate the feasibility of selection for growth of Nile tilapia in low-input environments.

The inability of tilapia to tolerate low temperatures is of major economic concern as it reduces their growing season and leads to over winter mortality. In this study, cold tolerance of juvenile Nile tilapia, Oreochromis niloticus, was investigated and heritability estimates obtained. A total of 80 maternal full-sib families were produced by mating each sire with two dams. Fry were grown in hapas suspended in earthen ponds fertilized with chicken manure, and were 41–91 days post-hatch at the start of the experiment (mean standard length 50.6 mm; mean body weight 5.1 g). Fry were tagged and exposed to low temperature in an indoor facility. Temperature was lowered from 16 °C to 11 °C in 48 h and from 11 °C to 8 °C at the rate of 1 °C/day. Cold tolerance was expressed as temperature at death (TAD) and cooling degree hours (CDH). Fish mortality started at 13.6 °C and total mortality occurred at 8.6 °C. Mean TAD and CDH were 10.1 °C and 298.07 respectively. Fish body weight (BW) had a highly significant effect on cold tolerance (P < 0.0001). Smaller fish (< 5g) were more susceptible to lower temperature than larger fish. The heritability of cold tolerance was 0.08 ± 0.17 for CDH and 0.09 ± 0.19 for TAD, estimated with an animal model. There was a considerable common environmental/full-sib effect for this trait (0.33 ± 0.10 for CDH and 0.27 ± 0.09 for TAD). These values indicate that estimation of genetic parameters for cold tolerance in tilapia should include both direct additive and common environmental effects. Based on the results of this study, we conclude that the most appropriate way of enhancing cold tolerance of tilapia juveniles is by husbandry practices that increase pre-winter body weights.

... a Regional Center for Africa and West Asia, The World Fish Center, Abbassa, Abu Hammad, Egypt. b Central Laboratory for Aquaculture Research, Abbassa, Abu Hammad, Egypt. c Department of Fisheries and Allied Aquacultures, Auburn University, Auburn, AL, USA. ...

... a, Regional Research Center for Africa and West Asia, The WorldFish Center, Abbassa, Abu Hammad, Egypt. b, The WorldFish Center, Jalan Batu Maung, 11960 Batu Maung, Penang, Malaysia. Received 1 July 2007; revised 14 March 2009; Accepted 16 March 2009. ...

It is well established that progeny of inbred matings are less fit than those of outbred matings, and that inbred individuals suffer from reduced viability and fertility. Inbreeding can be avoided by dispersal of progeny or by actively avoiding mating with kin (mate choice). We investigated the effects of sex ratio, relatedness (kinship coefficient) and level of inbreeding on the

... Mahmoud A. Rezk a , 1 , R. Oneal Smitherman a , John C. Williams b , Amy Nichols a , c , Huseyin Kucuktas a and Rex A ... brassy color, and pre-feeding behavior in small ponds which includes schooling and rapid swimming causing a rippling effect on the pond surface [Dunham ...

Ascertaining the appropriate selection environment for Nile tilapia (Oreochromis niloticus) in Africa is a critical issue. Two data sets derived from two selection lines originating from a common base population were analysed in this study. The lines were selected in two different input environments, here named ‘low input’ and ‘high input’. Both data sets were combined and jointly analyzed to