Hej,
Guldfisk och koi har inga problem att föröka (crossbreed). Mycket ful kan fisken bli och vissa påminner om den vilda karpen som båda härstammar från. Här beskrivs det rätt väl fast de hävdar att avkomman blir steril. Vad jag har sett kan den även bli fertil.
Koi (which is short for Nishikigoi) and goldfish are biologically similar enough to reproduce, but they are not the same species and their offspring will be infertile- like a donkey mating with a horse makes a mule. Koi are the species Cyprinus carpio. Normally goldfish and koi seem to prefer mating with their own species, but if they don't have a choice they will "love the one [they're] with"!
Butterfly koi are supposedly an interbreeding of koi and Indonesian carp, which are close relatives. There are other interbreedings between common carp and koi, but they are closer biologically so the lines are kind of fuzzy.
http://groups.yahoo.com/group/pondkeepers/message/869
> > I've also had some koi/goldfish hybrids. They tend to be on
> the
> > ugly side. Kind of tall from pectoral to dorsal with a long mouth.
<u>
Carassius auratus auratus</u>http://groups.yahoo.com/group/Ponds-Koi/message/750
http://www.koi.com.my/forum/KOI_Talk_C1/General_Discussion_F6/help....do_goldfish_and_koi_crossbreed_P5738/
http://www.akca.org/index/spboard/messages/862.htm
<b>Och denna siten är mycket bra för ditt arbete Nova...</b>
http://www.dpi.qld.gov.au/extra/aquaticinvaders/student_carp.html
Carp occasionally crossbreed with goldfish (Carassius auratus). <b>Further research is required to establish whether goldfish-carp hybrids are fertile. </b>
<b>Siterna hittar du under mitt inlägg på:</b>http://www.zoopet.com/akvarium/fisk.asp?NR=54
Böcker
http://www.aquariumhobbyist.com/bookstore/koi_db.htm
Säg till om du behöver mer (i doubt it though.. :o)