Growth and feed utilization in selected outbred families of rainbow trout ( Oncorhynchus mykiss )

The main objective of this study was to investigate the relationship between the breeding progress and the breeding aims expressed by the growth rate and feed utilization of four families of rainbow trout reared under identical conditions. The breeding strategy was family breeding: Fifty families were produced by mating individuals of 25 brood stock sires and 25 brood stock dams according to a partly factorial design. The experimental families were selected based on growth data from the parent generation. The families were half siblings two by two. The four experimental fish families A1, B1, C1 and D1 studied in year 1 were half siblings two by two. The families C1 and D1 showed the significant highest performance in respect of SGR and FCR as well as family C1 had the most efficient conversion of the ingested protein into meat gain. This means that even the overall paternal traits for slow growth individuals from the offspring may be genetically determined for good growth performance. The four experimental fish families A2, B2, C2 and D2 studied in year 2 were all full siblings. Family B2 demonstrated the lowest growth rate and the lowest utilization of the ingested feed compared to the other 3 families, which amongst them showed similar performances. Following, in this case the heredity for the trait of low growth rate was demonstrated. The fish families A2 – D2 showed overall higher growth rates compared to the families A1 – D1. And further was the time to achieve the individual fish weight of about 600 g about 1 month shorter with the families of the second experiment (A2 – D2). These differences in growth performance might be due to differences in rearing temperature. The first year experiment was run at an average temperature of 13.0 ± 1.2 C while the second year experiment was run at 16.8 ± 0.8 C due to technical circumstances. However, the overall minor differences in growth performance (SGR and FCR) between the families may indicate that the genetic differences between the four families and in particularly between the genetically distant families were not that large. Introduction In Denmark rainbow trout (Oncorhynchus mykiss) has been farmed in fresh water for more than 100 years, and Denmark has been among the main producers of rainbow trout in the world (From, 1993). But since 1986 environmental restrictions has been put on the aquaculture industry limiting the annual production to the current level of about 33 000 metric tons (FAO). In contrast, the European production of rainbow trout has been increasing and is currently about 300 000 metric tons per year (FEAP). However, breeding was acknowledged as a tool for more sustainable farming of rainbow trout. In order to improve the more sporadic breeding experiences made by individual farmers a systematic breeding program was initiated in the year 2000 at Danish Trout Breeding (DTB) – Jokumsen et al., 2001, Jokumsen, 2002. The success of a breeding program is to a great extent dependent upon the amount of additive genetic variation for the traits in question within family groups of rainbow trout as well as favourable genetic correlations among these traits (Henryon et. al. 2002). Breeding objectives as improved growth and feed utilization expressed by the specific growth rate (SGR) and feed conversion ratio (FCR), respectively, are quantitative measures of productivity and efficiency in development of sustainable aquaculture production (Thodesen et al. 2001, Kolstad et al. 2004). Breeding programs are also valuable tools to control the age at sexual maturation and to improve resistance to specific diseases (Fjalestad et al 2003, Henryon et al., 2005). In farming of salmon breeding progress of 10 % per generation (4 years) in terms of growth rate and feed utilization has been reported (Gjedrem 2000). The breeding goals of the Danish breeding programme were specific growth rate (SGR) and feed conversion ratio (FCR). Accordingly, the selection of brood stock from the families was related to improved growth and utilization of the feed. The breeding strategy followed were family breeding crossing the individual males and female fish according to a factorial design. Based on growth and breeding data 8 families were selected for the growth and digestibility experiments and quality assessment. In two successive years (2002 and 2003) growth studies were carried out with 4 selected families from the breeding station. The 4 selected families from the 2002 and the 2003 generation, respectively, were of similar age and size. The investigations included: Specific Growth Rate (SGR) Feed Conversion Ratio (FCR) Weight/length relationships (condition factor) Productive Protein Value (PPV) Mortality Aim The primary aim of the study was to investigate the relationship between the breeding aims and the obtained breeding progress expressed in terms of specific growth rate (SGR) and Feed Conversion Ration (FCR) of market size rainbow trout (Onchorhynchus mykiss).