Torild Johansen

Variations in growth in haemoglobin genotypes of Atlantic cod

In the present paper are described the growth properties of three different haemoglobin genotypes of juvenile Atlantic cod (Gadus morhua) reared at 7, 10, 13 and 16 °C. In addition one group was reared under “temperature steps” i.e. moved successively from 16 to 13 and 10 °C. The genotype Hb-I(2/2)displayed the overall highest growth rate in the temperature range 13–16 °C, whereas the Hb- I(1/1)genotype showed the highest overall growth at the lowest temperature (7 °C). Accordingly, we found a significant interaction between genotype and temperature. The differences in growth were largest when cod were reared under the temperature step regime where the Hb-I(2/2)genotype displayed 17 and 24% higher growth than Hb-I(1/1)and Hb-I(1/2),respectively. Optimal temperature for growth (Topt.G) varied between the genotypes with the genotype Hb-I(1/2)displaying the highest (mean ± SE) Topt.G (14.5 ± 1:0.8 °C) and Hb-I(1/1)the lowest (12.5 ± 0.2 °C). The biological significance of this link between biochemical genetic variation and physiological properties might be the influences on growth pattern, ultimate size and age at first maturity.

Strict conservation of the ITS regions of the ribosomal RNA genes in Atlantic cod (Gadus morhua L.)

The nucleotide sequence of the internal transcribed region (ITS) of ribosomal RNA genes from Atlantic cod (Gadus morhua L.) was determined. The complete ITS region spanned approximately 1113 base pairs. The ITS1 region comprised 532 base pairs, the 5.8S region 159, and the ITS2 region contained 422 base pairs. Sequence data were obtained from a total of 12 samples, one pool from six cod and 11 individuals. The sequencing was carried out in two separate experimental periods employing slightly different methodology. The samples were from two different cod stocks, Norwegian costal cod and North East Arctic cod. The sequence analysis showed that in the 12 samples, the ITS region, including the 5.8S RNA, was identical. The ITS region is thus totally conserved in these two cod stocks. The extreme conservation of the ITS regions in the cod rDNA could reflect the small genome size of cod and/or indicate a specific critical role in the processing of the ribosomal units in cold-adapted species.