Missouri’s state hatchery systems have experienced recurring early-life mortalities in hatchery reared rainbow trout (Oncorhynchus mykiss), primarily during the sac-fry to fingerling stages. These losses are consistent with thiamine deficiency complex (TDC), a condition linked to insufficient maternal thiamine transfer during egg development. Thiamine is essential for metabolic and neurological functions, and its deficiency can cause ataxia, corkscrew swimming, lethargy, and reduced immunity leading to elevated mortality due to secondary bacterial infections.
This study is evaluating whether maternal and/or egg-stage thiamine supplementation reduces early-life mortality and improves early growth of hatchery-reared rainbow trout. A controlled experiment was conducted using four treatment groups: thiamine-injected females + thiamine egg baths (T1), thiamine-injected females + sham bath (T2), saline-injected females + thiamine egg bath (T3) and saline-injected females + sham bath (T4: Control). Each treatment was replicated three times.
Measured parameters include fecundity, egg diameters at water hardening, hatch success, fry survival through 60 days post hatch (DPH), yolk sac absorption rates, and thiamine concentrations in eggs before and after treatments. Preliminary results indicate offspring from T2 and the Control, T4 exhibited the lowest mortality (Figure 1). Improved body condition was observed in thiamine supplemented groups (treatments: T1, T2, and T3) (Figure 2). This study suggests that thiamine supplementation in maternal and egg-stage has limited effects on early-life mortality in hatchery-reared rainbow trout. However, it may contribute to improved early growth and body condition. Further research is needed to understand the mechanisms driving these effects and to identify supplementation strategies that optimize both survival and growth. Data on fish mortality, growth, fecundity and egg size will be presented.