Amazon: Secrets of the Golden River

A great deal of common freshwater fish in the hobby come from the Amazon River Basin, and with good reason as it's the second largest freshwater river system in the world. Angelfish, discus, and many species of cories and tetra are all only found in the Amazon. Due to the wide variety of species Amazon biotopes are very common. This documentary includes footage of many of these and other Amazon fishes in the wild.

I do not own or claim to own this video.

Differences Between Goldfish and Koi

I know there are a lot of similarities between these two fish, but getting them mixed up is one of my largest pet peeves. Maybe this is because I’ve kept both species of fish for many years. Maybe it's because I dislike people who don't bother to think about what they are seeing. Either way, I would like to point out the major differences between koi (Cyprinus carpio) and goldfish (Carassius auratus auratus).

Size

This is the most obvious difference between adult koi and goldfish. If you see a colorful fish in a pond that is larger than 15 inches, it is a koi. Fishbase.org lists 12.5 in (32 cm) as the maximum size for goldfish while it lists 43 in (110 cm) as the maximum size for koi. Younger specimens in ponds can be more difficult to tell apart, though, so this isn't always reliable.

Coloration

Goldfish are pretty limited in their patterns and colors whereas koi have a much wider variety. Goldfish tend to come in solid colors of orange, white, black/blue, or red. Yellow can be seen but is very uncommon. White and black combinations and red and black combinations are also possible but rare compared to the common red and white combination. Koi come in a much greater variety of common combinations. The base colors are red, white, black, yellow, orange, and blue. The chart below illustrates some common koi colorations and the names of the patterns. 

Koi color varieties (credit in picture)

The barbels (sometimes called whiskers)

This is the most obvious difference between koi and goldfish. Koi will have these barbels and goldfish will not. If you can see these on a pond fish, that fish is a koi. However, these aren't always easily observable. 

Barbels on koi (Stan Shebs @ Wikipedia)

The Tail

Both koi and goldfish can have elongated tails, but only goldfish will have the signature double-tail. This is where the caudal fin (tail fin) is doubled. From above, this will often give the tail a three-pronged or a four-pronged appearance. This characteristic is only found in goldfish. 

Typical split caudal as seen on wakin goldfish (fishsempai.com)

Other less obvious physical characteristics

This illustration below points out more of the morphological differences between koi and goldfish. Often times these aren't visible unless you view two fish side by side or have looked at a lot of koi and goldfish. The difference in mouth is often visible when you feed them. Sometimes it will give you a chance to look for barbels, too. 

Physical differences in koi and goldfish (credit unknown)

 

Can they interbreed?

Yes. When found in the same habitat (either in the same pond or in the wild), the two species will hybridize, but the hybrids are infertile. Often times these hybrids will be the natural brown, but some can come out a beautiful solid black. When these are found in the aquarium trade, they are often breeding mistakes. 

Genetically verified hybrid carp goldfish found in the wild (Jim Negus)

I hope you now have a better understanding of the differences between goldfish and koi. These are two beautiful fish that deserve to be recognized for their own merits.

Color Changes in Bettas

As anyone who has keep bettas for a long period of time knows, they are apt to change colors. What you see in the cold cup in the store is never what you will see after a few days of warm, clean water in your tank. For this reason, bettas bought in pet stores are often gambles. You can buy a pretty white one in the store and it will turn a peachy-yellow in a few days. There are three reasons why bettas change colors: stress, age, and genetics.

Stress

All fish are known to change colors when stressed. Most of the time this is a whiting out or a dulling of their colors. In pet stores almost all fish are stressed. The tanks are crowded and often contain diseases. While the cold cups may not always contain disease, they will stress tropical fish like betta. And just like any other fish, the colors of the betta will dull and fade. The transformation from stressed fish to unstressed fish can take a matter of hours or sometimes days. This is the main reason betta change color when you first get them. 

This is the same betta. On the left is the betta in a cold cup in the store.
On the right is after a month of being in clean, warm water.

Age

Often the fish you see sold in store aren't very old. Typically the smaller they are, the younger they are. Their colors haven't fully developed yet and neither have their fins. So essentially what you are buying is a "work in progress." Some will change more than others as not all bettas being sold are the same age. Below is a very young betta that I bought in July 2011.

This image shows the same betta from July 2011 to February 2012.
Notice the longer fins and more pronounced color.

Genetics

Some betta carry what is called the marble gene. This gene sequence causes the betta's colors to  changing even after they should have stabilized with age. Sometimes the betta will continue to change his whole life even looking like a whole different fish a year after you buy him or her. Sometimes the betta will "marble out" and become a cellophane, and some "unmarble" and turn a dark, solid color.  There is no way to predict what you will end up with. This presents an interesting challenge to breeders, and they can be a neat fish to have as a pet. A month later you can end up with a completely different fish than you started with!

This is my marble plakat. The image on the right is from July 2012. The middle image is a
month later. The far right image is from October 2012. My marble has unmarbled
to a beautiful solid blue.

 

Works Referenced

Parnell, Victoria. 3 Mar 2006. "The Ever-Changing Marble." bettysplendens.com. Retrieved 4 Nov 2012.