PICHA, M.E.*; FRUCHTMAN, S.; NOGA, E.J.; BORSKI, R.J.; North Carolina State University, Raleigh: Increases in insulin-like growth factor-I during compensatory growth in a teleost fish

Compensatory growth is an accelerated growth state that exceeds normal rates when animals are alleviated of certain growth-stunting conditions. Little is known of the hormonal control of compensatory growth in teleost fishes. Our aim was to examine if compensatory growth occurs in hybrid striped bass (HSB, Morone chrysops x M. saxatilis ) and evaluate whether changes in insulin-like growth factor-I (IGF-I) accompany the response. Age 1+ HSB underwent a prolonged period of cold-banking (14�C) and maintenance diet (0.6% bw/d) before subsequent acclimation to more ideal environmental conditions (23�C, ad libitum feeding (2x/d)). Age 1+ fish showed an immediate and dramatic increase in both body weight and length compared with sized-matched, Age 0+ fish. By 127 days, 1+ fish weighed 150% more than 0+ fish. Specific growth rate was also higher in 1+ compared with 0+ fish for the first 70 days. Circulating IGF-I was 3-fold higher in Age1+ versus 0+ fish by day 37. Although values began to converge thereafter, clear disparities in plasma IGF-I levels could be seen throughout the remainder of the experiment. Despite an increase in specific growth rate of Age 1+ fish during the initial onset of compensatory growth, no difference in IGF-I was seen between these and 0+ fish during the first week of the experiment. A recovery in the hepatosomatic index of Age 1+ fish toward values of Age 0+ fish was observed during this period. These results suggest that HSB undergo compensatory growth and that circulating IGF-I may be an important mediator of the accelerated growth rates associated with this phenomenon. It also appears that other factors may be critical to the initiation of compensatory growth, including the restoration of depleted energy stores.