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Genetic parameters and selection responses were obtained for harvest body weight of blue tilapia ( Oreochromis aureus) from data collected over three generations in a selected population. A total of 18 194 records representing 186 sires and 201 dams were used in the analysis. Within generation heritability estimates for harvest body weight ranged from 0.18 to 0.58. When data from more than one generation were included in the analysis, heritability estimates became more stable (0.33-0.40) and it was 0.33 when all data were included in the analysis. The common full-sib effect accounted for 10% of the phenotypic variance in the full data set. Heritability for survival from stocking to harvest was estimated at 0.01 and 0.09 in actual units (fitting an animal model) and in the logit (sire model) scale respectively. The genetic correlation between harvest body weight and survival was 0.22 and not significantly different from zero. The total selection response for harvest body weight over the three generations of selection measured as the difference between least-squares means of selected and control lines was 17.7%. The corresponding figure when response was measured as the difference between mean breeding values of selected and control lines was 19.6%. The average inbreeding coefficient was 0.003 after three generations of selection. These results indicate that there are good prospects for the genetic improvement of harvest body weight in blue tilapia. [ABSTRACT FROM AUTHOR]

This study was aimed at detecting differences among tilapia species in immunological and biochemical parameters that are indicators for fish health. In addition, six blood parameters that are indicators of stress were measured, glucose concentration, ceruloplasmin activity, lysozyme activity, respiratory burst activity, haematocrit and leucocrit, and their levels were compared among groups. A calibration experiment was conducted with commercial stock of tilapia to optimize a protocol for measuring stress response in tilapia. An air exposure stress was induced to six groups of fish and blood samples were taken at six different times: 15 min, 1, 2.5, 4.5, 6 and 24 h, after inducing stress. The highest responses to stress were observed after 2.5–4.5 h. A second experiment was conducted with four tilapia species:Oreochromis aureus(Steindachner),O. mossambicus(Peters), a red strain and the wild type ofO. niloticusL. Levels of serum biochemical components and parameters of the innate immunity response to stress were compared in ten fish from each species. Significant differences were observed.Oreochromis aureusdiffered from the other three species (notably fromO. mossambicus) in most of the measured immune response traits (glucose concentration, lysozyme activity, haematocrit and levels of total protein and IgM after stress) and serum biochemical components (protein, albumin, triglyceride, cholesterol, calcium, magnesium, phosphorus, bilirubin andβ-hydroxybotiric acid). The identified differences suggest that hybrid families fromO. aureusandO. mossambicusmay be used to construct a segregating population for genetic analysis of the innate immune response to stress. Thus, these two species were bred for segregating F2 population, suitable for quantitative trait loci studies for the innate immune response to stress. [ABSTRACT FROM AUTHOR]