how can you tell the gender?

[brandoniscool]

Hi my name is Elisha I am in Mr Rutherford class we have a 160 gallon tank [including auto-top sump tank] in our classroom there are different fish in our main tank but how can I tell if their a male or a female? is it about the size that change their gender? or is there more than comparing the size, is there a another way to compare the gender I wonder this because i have two goldfish at home one is big the other one is small that also made me wonder why does the smaller fish is a male but why not female is small as the male fish?
thanks for your help!

[Josh40996]

Hello Elisha, for each species of fish the technique for determining the gender of the fish is different and sometimes impossible (without looking at their reproductive organs) to tell.

For example, in a mated pair of clownfish, the larger of the two is the female. In Mandarin Dragonets, males have a spiked dorsal fin whilst the female has a rounded dorsal fin. In Fancy Guppies, the males have a gonopodium and are generally much more colourful than the females.

As for question on why the females are generally larger, I do not know I would like to take a guess on saying that it would be something to do with that the females would need a larger body for egg production? But I am sure someone more knowledgeable would be able to correct me

Keep of Reefin!

[MondoBongo]

when you can tell the genders of species apart it is known as Sexual dimorphism.

http://en.wikipedia.org/wiki/Sexual_dimorphism

many of our fish do exhibit sexual dimorphism, but plenty do not. some, like clownfish, are even able to change their gender based on environmental condition.

good examples of sexually dimorphic fish are the Madarin dragonet (Synchiropus splendidus) and the McCosker's Flasher Wrasse (Paracheilinus mccoskeri).

in S. splendidus specimens the males have an elongated dorsal fin, while the females do not.

here you can see the male with the enlarged dorsal spine:



and here is the female, lacking the dorsal spine:



and with P. mccoskeri the male is very brightly colored and has larger fins, while the females have a more streamlined fin shape and drabber colors.

here is the male:



and here is the female:



many fish do look the same though, or are able to change. so the only definitive ways to tell would be a necropsy, or observing them laying eggs or bearing young.

[snorvich]

And congratulations on your interest in marine fish. Keep asking questions, life is full of interesting ones!!

[Misled]

Originally Posted by snorvich

And congratulations on your interest in marine fish. Keep asking questions, life is full of interesting ones!!

That

My Pajama Cardinals

Male


Female

[davocean]

And then things get even more interesting when we include the hermaphrodites, anthias that start off as females, then the dominant one will become a male.
Clownfish begin as males, then the dominant will become a female.
In real life Nemo's Dad would have become Nemo's Mom!