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Venomous Fish vs. Poisonous Fish

Eileen here. A lot of people who come into our store see fish like our lionfish and scorpionfish and ask if they are poisonous. The answer? Technically, no. They’re venomous.

People also see warnings on some cucumbers, Sea Apples and Boxfish that they are poisonous and wonder if they might get a painful bite or sting. The answer? Probably not.  They’re poisonous.

So, what’s the difference that makes the lionfish venomous but the boxfish poisonous? The key is all in how the toxin is delivered. The term “toxin” simply means a harmful substance produced naturally by an organisms and is used for both venomous and poisonous animals. Venomous animals inject their toxin into their target using spines (lionfish, stonefish, rabbitfish), teeth (sea snakes, Blue Ring Octopus), or specialized stinging cells known as nematocysts (jellyfish, anemones, some corals). Some of these animals use their venom to hunt; jellyfish and anemones paralize whatever prey is unfortunate enough to end up in their tentacles before they draw the prey to their mouth. Others like the lionfish and rabbitfish only rely on their venomous spines as defense against being preyed upon themselves. This venom can range from very mild as in the case of anemones to fatal. The Blue Ring Octopus is one of the most toxic animals on the planet and has no known antivenom. People who are sensitive to bee stings are much more likely to have a severe reaction to common venomous animals in the aquarium trade like lionfish and anemones.

Mbu PufferPoisonous animals like boxfish, puffers or sea cucumbers, on the other hand, rely on their target absorbing the toxin. This can happen across any membrane – through the skin or gills, in the stomach or digestive tract, even in the lungs. Poison is used almost exclusively as a defense mechanism. Puffers and boxfish have special toxin in their bodies – usually the liver, ovaries and skin – that they can release when they are stressed to hopefully deter any possible predators. Unfortunately, in a closed system like an aquarium, this toxin can eliminate an entire tank – including the puffer or boxfish itself. Some groupers like the Clown Grouper also have a similar toxin in their slime coat. Cucumbers, especially the large Sea Apples, can also poison a tank if they are stressed, picked on or dying. These animals can be deadly in an aquarium but aren’t much of a threat to aquarists; if in doubt, use gloves when handling any of these animals, especially with any open wounds or cuts.

Whether venomous or poisonous, harmful or peaceful, the keywhen dealing with any animals is knowing what they are capable of and how to handle them properly. Being able recognise when an animal is stressed or how it defends itself is important in knowing how to keep that animal, its tankmates and yourself safe and happy.

Monsters from the Deep?

Hello, Dave here.

When most people think of giant fish, they imagine some behemoth dwelling at the bottom of the ocean. While the world’s oceans certainly have their share of massive fishes, most people are probably unaware of what may be lurking in the freshwater lakes and rivers of the world, some of them right here in the U.S.

What brought this blog to mind was a recent article that I came across that chronicled the recent capture and tagging of a Giant Freshwater Stingray by British Angler and Scientist, Ian Welch.Giant Freshwater Stingray The Stingray that Ian Caught is thought to be one of the largest fish ever caught of rod and reel. The Giant Freshwater Stingray (Himantura chaophraya) was caught in Thailand’s Maeklong River while on a research expedition. This stingray was estimated to be over 265kg (584lbs) and over 3.5m long. Some reports exist of these giants reaching sizes of 16.5 feet (5 meters) long and weighing up to 1,320 pounds (600kg). That is a big fish!

Not to be outdone is another giant native of Thailand, the Mekong River’s Giant Catfish (Pangasianodon gigas), which can reach lengths over ten feet and 650 lbs pounds. Both of these Thai giants are endangered species, and have been overfished for many years.

China has its share of freshwater giants also. One of the most bizarre giant freshwater fish of the world is the Chinese paddlefish (Psephurus gladius). This giant has been said to reach an amazing 23 feet (7 meters) in length and weigh up to half a ton (450kg). Another Chinese monster fish is the Giant White Sturgeon. The Giant White Sturgeon, who along with the Paddle fish is native to the Yangtze River, reaches 12 feet and weighs more than 950 pounds. Sadly, both of these fish are on the brink of extinction in China due to overfishing, pollution, and loss of habitat.

ArapaimaThe Americas have their share of freshwater giants as well. Native to the Amazon River basin in South America, the Arapaima (Arapaima gigas), can reach lengths of 10 feet and weighing as much as 400 pounds or more.

North America has a few noteworthy big fish, too. The Alligator Gar can weight up to 300 pounds and is commonly found along the Mississippi River basin, as well as many other southern states. They are very common to Florida’s Everglades. The Alligator Gar can reach up to 10 feet, and some historical accounts have them even larger than that!alligator gar

North America also has some large sturgeon species native to its waters. The White Sturgeon can be found in the rivers and estuaries of western Canada, and Northwest United States. I am not sure if this is the same species that is found in China, but in 2005 an 11 foot, 1000lb specimen was caught in British Columbia’s Frazier River.

lake sturgeonsLake sturgeons (Acipenser fulvescens) are common to the great lakes, and many other large cold water lakes in northern states, These fish have many accounts of specimens topping six feet (two meters) long and weighing over 200 pounds (90 kilograms).

So as you can see, there are quite a few large freshwater fish, you don’t need to explore the far reaches of the ocean to find them, some may be in your neck of the woods.

One thing that I must also mention is that some of these fish are sometimes seen for sale as aquarium fish. Obviously, none of them are suitable for aquariums and should not be kept as such.

Until next time,

Giant stingray image: guardian.co.uk
Arapaima Image: Wikipedia

Our Favorite Aquarium Books

Desiree and I have both shared some of our favorite aquarium websites and virtual reference, but what about those times when you want a real, live, glossy-paged, paper-cut-compatible BOOK? Well, just in time for the holiday shopping and wish list season, here are a few of our favorites of those, too.


  • Dr. Axelrod’s Atlas of Freshwater Aquarium Fishes and Dr. Burgess’s Atlas of Marine Aquarium Fishes
  • These two books are some of the classic tomes of aquarium fishes. Both contain literally thousands of species of fish as well as some basic information about each one. These books won’t help with aquarium-related details, but they are must-haves for identification and sheer volume of the animals covered.
  • Pocket Expert Guides (Reef Aquarium Fishes and Marine Fishes, both by Scott W. Michael, and Marine Invertebrates by Dr. Ronald L. Shimek)
  • This series is one of my personal favorites. Compact in size, but certainly not in information, these books are written with the aquarist in mind. They each contain well over 400 species of animals with detail on care, compatibility, aquarium suitability, maximum size, minimum tank size and other pertinent information. It’s a great series to take to the fish store with you for a quick reference on your new purchases.
  • “The Simple Guide” and “Super Simple Guide”series
  • This is the perfect series for new aquarists and is one of the first we tend to recommend when someone mentions “I’m thinking about starting a _______ aquarium”. The information is presented in a way that isn’t overwhelming to new aquarists and provides a complete view without getting too bogged down in scientific equations and technical terms. No matter what type of aquarium you have or are thinking about getting, there is probably a Simple Guide for it.
  • Reef Invertebrates: An Essential Guide to Selection, Care and Compatibility, by Anthony Calfo and Robert Fenner
  • I think we are currently on our…fourth?…copy of this book in our Fish Room because our employees wear it out reading and re-reading it during their lunches and free time. Lots of information about a wide range of invertebrates. A good read for “Reef” and “Fish-only” aquarists alike.
  • Corals: A Quick Reference Guide, by Julian Sprung
  • Ever see a new coral that you absolutely must have, but you know nothing about it? Look it up in here. Ever see a coral but can’t figure out what it could possibly be? Look through here. Need ideas about what new corals you could add to your existing reef tank? Browse this book. Lots of common aquarium corals with compatibility, identification and propogation basics.
  • Aquarium Fish magazine
  • Ok, so its not technically a “book”, but it still counts. This monthly magazine is by aquarists and for aquarists. It includes information on both freshwater and marine aquariums and is geared towards new and experienced hobbyists alike. I have a binder filled with past articles that I just HAD to save from this magazine. The new species profiles alone will never let us run out of new animals and aquariums to try at home.

Have any favorites I didn’t mention? Looking for a good book on a particular subject? Let us know!



Feeding Egg Yolk to Fish Fry

Ever wake up one day, take a look in your tank and see a horde of tiny little baby fish that weren’t there the night before? Did you have to run out in search for something to feed the new little fish? Here’s a quick and nutritious solution that you probably already have on hand…egg yolk! Yep, normal old chicken eggs that are probably already in your refrigerator. Just hard-boil an egg and remove the yolk (you won’t need the white, feel free to munch on that while you prepare the fishes’ portion). Put a small piece of the yolk in a small container of water and shake it up until the yolk is completely suspended in the water. You may want to break it up a little before you start to get a headstart but if you still notice larger chunks in the water that haven’t broken up enough, you can strain the mixture through cheesecloth or a coffee filter to get rid of the bigger pieces. Once the yolk is suspended in the water, just add a little to the tank with the fry. It’ll make the water a little cloudy so you don’t need to add much and you can save the mixture for a few days in the refrigerator.

Quick, easy, and healthy for just about any small fish fry!

Great Fish and Aquarium Information Websites

Hi, Desiree here.

Have you ever stopped to think where we’d be if the internet didn’t exist?  Probably stuck at the library. (Believe it or not they DO still exist!)  But, although I am a fan of books and the knowledge they contain,  the information in them can be out-dated as soon as it’s printed.  These days, our source of information is online.  If there’s anything we need to find, we can almost certainly find it on the Google machine.  As biologists and hobbyists, the internet is a valuable and fun source of information.  As we “fish” for information we often find great websites dedicated to one single class or family of animal, both fresh and salt water.  Some of these sites are public forums full of shared knowledge and experience, others are more scientific in their classification and identification, some are a combination of both.  I wanted to share just a couple of my favorite links, sites I use frequently to identify fish or find fun new species to offer in the store.  Check these out, and have fun online!  Surf’s Up!

http://actiniaria.com/  A site dedicated to sea anemones; not all can be kept in aquaria, but are still really cool to look at.

http://www.seaslugforum.net/  Exactly what it sounds like.  Again, most you’ll never see in any store, but the pics are awesome!

http://tolweb.org/tree/phylogeny.html  A site for us true fish nerds, heavy on phylogeny and nomenclature – fun to explore but not for identification of a single animal.

http://www.planetcatfish.com/index.php  Awesome freshwater catfish site – great for looking up L- or C- numbers.

http://www.loaches.com/species-index  Another freshwater site – fun for loach lovers!

http://puffernet.tripod.com/main.html  A personal favorite – freshwater and brackish puffer info.

And we can’t forget to mention these two:  a wealth of hobbyist information –



Feel free to send along any of your favorite websites, or comments on the ones I’ve listed.

Until next time,