2 Study on the growth of salmon
Prof. Shimizu's Laboratory of Field Science Center for Northern Biosphere
Prof. Shimizu's Laboratory of Field Science Center for Northern Biosphere
Our
goals are to understand the mechanism of growth regulation and utilize
hormones/proteins involved in growth regulation as indices to evaluate growth
status. Our focus is on insulin-like growth factor (IGF)-I and its binding
proteins.
Growth
of fish is influenced by various environmental factors such as photoperiod,
water temperature, feeding ration and stress. Such stimuli are integrated by
the brain and hormones regulate growth. Growth hormone (GH) and insulin-like
growth factor (IGF)-I are two major hormones regulating growth. GH stimulate
growth directly acting on target tissues such as muscle and bone or indirectly
through stimulating hepatic production of IGF-I. This system is called “the
GH-IGF-I system”. Circulating IGF-I mediates action of GH and has a negative
feedback effect on the secretion of GH from the pituitary gland.
Most circulating IGF-I is bound to one of six IGF-binding proteins (IGFBPs). IGFBPs can inhibit or stimulate the activity of IGF-I depending on the type, post-translational modification and microenvironment. Thus, IGFBPs play a key role in modulating growth. Teleosts have up to 12 IGFBP subtypes due to the third-round whole genome duplication in this lineage. In addition, salmonids are tetraploid origin and thus have 22 subtypes.
Goal: We are interested in unraveling functions of IGF-I and IGFBPs in salmonids and utilize them as indices of growth. Availability of growth indices is useful to improve aquaculture and resource enhancement.
Three major IGFBPs are detected in serum/plasma of salmonids. They are believed to inhibit or/and promote action of IGF-I.
Functional analysis using recombinant IGFBP-1a and -1b revealed that IGFBP-1a inhibited the action of IGF-I on GH release from the pituitary gland.
Circulating IGF-I and IGFBP-2b positively correlated with individual growth rate whereas a negative correlation was seen between IGFBP-1b and growth rate. These results suggest that they are useful as growth indices.
Growth status of out-migrating juvenile chum salmon was monitored by using serum IGF-I as a growth index. The results suggest that fish under poor growth condition stayed in the estuary and might suffer growth-dependent mortality thereafter.