Induced Spawning of the
Margined Madtom
J.N. Stoeckel, R.J. Neves-2001
North
American Journal of Aquaculture, 63(2): 99-108
Abstract:
Daily hormonal injections of male and female margined
madtoms Noturus insignis induced captive spawning of 59 of 77 fish.
Two injection treatments proved effective. Mean total dosage for one of the
treatments was 5,372 IU human chorionic gonadotropin/kg plus 56 mg carp
pituitary extract/kg; the other treatment was 572 µg LHRHa/kg plus 57 mg
domperidone/kg. Of the 59 females induced to ovulate by the two hormonal
treatments, 47% of them ovulated approximately 2 d after the first hormonal
injection and 92% of them had ovulated within 4 d of the first injection.
Inclusion of more than one breeding pair of margined madtoms per tank
inhibited tank spawning, but females in tanks containing multiple pairs of
fish ovulated and could be stripped. Embryos did not develop in 6 of 11
tank-spawned egg masses or from any of 19 strip-spawned egg masses. Margined
madtoms consumed tank-spawned egg masses when spawners were not removed from
the nest. Oocyte diameter (>/= 3.5 mm) and germinal vesicle position
(>90% toward the edge of the oocyte) can be used to determine which
females will respond to hormonal treatments. However, catheterization to
determine oocyte stage inhibited ovulation. Critical topics of research,
before these techniques are applied to rare species, include refinement of
oocyte staging methods and greater assurance that spawned eggs are
fertilized.
(Virginia Cooperative Fish and Wildlife Research
Unit, Department of Fisheries and Wildlife Sciences, Virginia Polytechnic
Institute and State University, Blacksburg, Virginia 24061, USA)