Growth performance, body composition and plasma thyroid hormone status of channel catfish (Ictalurus punctatus) in response to short-term feed deprivation and refeeding

A 6-week feeding trial was conducted to investigate the effects of short-te rm feed deprivation on inducing compensatory growth and changes in thyroid hormone levels of channel catfish. Feeding treatments consisted of the foll owing four regimes of 2-week duration: satiate feeding (control), no feed f or 3 days then feeding to apparent satiation for the next 11 days, no feed for 5 days then feeding to apparent satiation for 9 days, and no feed for 7 days then feeding to apparent satiation for 7 days. These regimes were rep eated three times over the 6-week trial in which 25 channel catfish fingerl ings, initially averaging 15 g each, were stocked into each of 12, 38-l gla ss aquaria supplied with supplemental aeration and flow-through water. Depr iving fish of feed had a pronounced effect in that fish lost weight in as l ittle as 3 days. Returning the fish to a satiate feeding regime caused a re sumption of growth, equal to control growth only in the case of the 3-day d eprived treatment, but all periods of feed deprivation failed to induce a p eriod of catch-up growth adequate to compensate for previously lost weight. Feed efficiency also was not improved by the periods of feed deprivation, and restricting feed in excess of 3 days lowered feed efficiency. Fish cond ition indices were not altered at the termination of the trial. Muscle lipi d, muscle protein and liver protein also were not different among feeding r egimes. Liver lipid was elevated in fish deprived of feed for more than 3 d ays every 2 weeks. Plasma thyroxine (T-4) and triiodothyronine (T-3) were e qually depressed by 3 days from the onset of feed deprivation. Both hormone s rose significantly within 24 h of realimentation, with the greatest incre ase observed in animals subjected to the briefest feed deprivation. These r esults support a role for thyroid hormones in the promotion of growth in ch annel catfish. Whereas feed deprivation appears to rapidly reduce activity of the hypothalamo-pituitary-thyroid axis, the high correlation observed be tween T-4 and T-3 in all treatments suggests that peripheral deiodinating s ystems are capable of rapidly generating T-3 from T-4 upon realimentation. More rapid recovery of thyroid hormone production following realimentation may minimize the effects of feed deprivation on growth and feed efficiency of fish subjected to the 3-day deprivation treatment when compared to longe r periods.