A number of factors, including the 5'UTR, may help to explain why no similarity was found for these sequences, but the unusual biology of salmon and the fact that the sequences are from pre-smolt fish may be contributory factors.
From time course studies of experimentally infected Atlantic salmon post-smolts, fish exhibited different outcomes of infection and disease.
Second, after becoming smolts, fish now encounter low water velocities in the reservoirs in lower Snake River as a result of construction of four dams in the 1960s and 1970s.
It is, therefore, overly simplistic to make statements such as: the fastest growing parr are expected to mature, the next fastest growing to smolt as young fish, and the remainder to smolt as older fish.
Sometimes the fastest growing fish are predicted to smolt immediately, slightly slower growing fish are predicted to mature as parr, and even slower growing fish are predicted to smolt at older ages (e.g. Fig. 8B), with the result that residency is associated with intermediate rather than fast or slow growth.
For the American River, we consistently predict that the vast majority of fish will smolt and emigrate at age 1 (as observed in the field) for almost all combinations of survival scenarios (Table 2).
Our empirical observations indicate that the American River is dominated by anadromous fish smolting at young ages.
Because precocity possibly interferes with normal progress through the parr-smolt transformation, the relative decrease in vasotocin we observe in precocious fish may be linked to an early regulatory effect on osmoregulation, and the variation we observe in the non-precocious individuals may be due to early preparation for smolting in some fish.
Third, future anadromous fish undergo parr smolt transformation (smoltification), adapting them for a life in the marine environment, and seawater adaptability is highly size-dependent (Jones 1959).
