The potential of microsatellite sequences as genetic markers in channel catfish (Ictalurus punctatus) was investigated with respect to their variability, inheritance, and usefulness in related species. Six small insert genomic DNA libraries enriched for six families of microsatellites of channel catfish were constructed. We describe here the isolation, characterization, and PCR amplification of 32 microsatellites from channel catfish. The flanking primer regions of microsatellite loci were highly conserved between channel catfish and blue catfish (I. furcatus). Of the 32 loci, 29 were amplified from blue catfish using primers designed from channel catfish, indicating conservation of primer binding sequences. Most of the amplified alleles from channel catfish and blue catfish were polymorphic. White catfish (Ameiurus catus) and flathead catfish (Pylodictus olivaris) loci were also amplified. The microsatellite markers are highly polymorphic for all catfish species tested and are inherited as codominant markers. They should be highly useful for construction of genetic linkage maps of catfish and for marker-assisted selection.

Expressed sequence tag (EST) analysis was adopted to address physiological changes after injection of carp pituitary extract for induction of ovulation. ESTs were analyzed from cDNA libraries constructed from mRNA isolated from channel catfish (Ictalurus punctatus) pituitaries before and after induction of ovulation by injection of carp pituitary extract. One hundred randomly picked clones were analyzed. Of the sequences generated, a large percentage (59%) of ESTs were identified as known genes by identity comparisons. These 59 clones of known gene products represent transcriptional products of 30 genes. The 41 clones of unknown gene products represent 33 genes. Expression of gonadotropin (GtH) -subunit (149%) and prolactin (176%) was slightly enhanced as a result of induced ovulation. Large increases in frequencies of several peptide hormones were observed as a result of induced ovulation: GtH -I, 486%; GtH -II, 933%; growth hormone, 393%; proopiomelanocortin (POMC), 345%. POMC represented about 21% of all transcriptional activity in the pituitaries after induced ovulation. This is the first study addressing physiological changes after injection of carp pituitary extract, a procedure widely used in catfish hatcheries.