Induced spawning of the margined madtom

Daily hormonal injections of male and female margined madtoms Noturus insig nis induced captive spawning of 59 of 77 fish. Two injection treatments pro ved effective. Mean total dosage fur one of the treatments war 5.372 IU hum an chorionic gonadotropin/kg plus 56 mg carp pituitary extract/kg: the othe r treatment was 572 mug LHRHa/kg plus 57 mg domperidone/kg, Of the 59 femal es 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 ov ulated within 4 d of the first injection. Inclusion of more than one breedi ng pair of margined madtoms per tank inhibited tank spawning, but females i n tanks containing multiple pairs of fish ovulated and could he stripped. E mbryos 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 masse s when spawners were not removed from the nest. Oocyte diameter (greater th an or equal to3.5 mm) and germinal vesicle position (>90% toward the edge o f the oocyte) can be used to determine which females will respond to hormon al treatments. However, catheterization to determine oocyte stage inhibited ovulation. Critical topics of research, before these techniques are applie d to rare species. include refinement of oocyte staging methods and greater assurance that spawned eggs are fertilized.