Indirect effects of eyestalk ablation
Considering that eyestalk ablation affects the hormone balance for numerous physiological processes in addition to stimulation of gonadal hypertrophy, what are the practical effects of this operation, and at what cost do we achieve induced ovarian development using eyestalk ablation? The following observations have been made concerning use of eyestalk ablation in captive reproduction, and may be related to either captive conditions, eyestalk ablation, or both:

  • Captive spawn size (number of eggs per spawn) is smaller than in wild-matured females, regardless of whether eyestalk ablation is used.
  • Eyestalk ablation increases total egg production in captivity by producing more frequent spawnings, but not larger spawns.
  • There is not a strong trend toward diminishing spawn size over time.
  • Molt cycle duration is shorter in eyestalk-ablated females than intact females.
  • Higher mortality of eyestalk ablated females is often, but not always, reported.
  • Eyestalk ablation has been suggested to deteriorate female condition.
  • Eyestalk ablation in some instances has been observed to produce lower hatch rate of eggs than unablated females.
  • Hatch rate has been observed to decline over time under captive conditions.
  • Ovarian color in captive females, especially in eyestalk ablated females, is often rather different than wild-matured (Bray & Lawrence, 1992).

There is strong circumstantial evidence that part of the problems seen with captive reproduction are related to a simple inability of current diets to supply required nutrients as rapidly as required for the gonadal hypertrophy stimulated by eyestalk ablation. In nature, an organism would not be anticipated to develop eggs, constituting some 10% of female body weight, unless nutrients are available for first, metabolism, second, growth, and third, reproduction. Eyestalk ablation accelerates the production of ova, regardless of whether the proper types and balance of nutrients are available, and regardless of whether those ova are even capable of fertilization. Dietary factors clearly have been shown to influence percentage hatch and percentage of females spawning (Bray & Lawrence, 1992).