That Fish Blog – Aquarium Advice and Information

Hello, Frank Indiviglio here. The ways of crabs never cease to amaze me, and we are fortunate indeed that so many interesting species do exceedingly well in marine aquariums. Today I’d like to draw your attention to certain hermit, arrow, boxing and spider crabs that increase their survival odds by carrying food or weapons wherever they go.

A Mutually Beneficial Partnership

After locating a suitably-sized sea anemone, the anemone hermit crab (Pagurus prideauxi) places the stinging invertebrate on its shell as a deterrent to predators. The anemone attaches itself to the new home, and may benefit by gaining access to leftovers from the crab’s meals. Anemone hermits that I’ve kept have invariably relocating their protectors when switching their own living quarters from one shell to another.

Anemones as Boxing Gloves

Another weapon-bearing crustacean, the boxing crab (Lybia tessellata), goes through even greater lengths to arm itself with stinging anemones. This tiny (2.1 inch) fellow has the fascinating habit of carrying small anemones about in its claws. When threatened, it will rear up on its hind legs and wave the “weapons” at the interloper!

Lunch to Go

The ever-popular arrow crab (Sterorhynchus seticornis) is more concerned about food supply than weaponry, and impales food upon its pointy carapace. This is quite comical to see, because, due to the location of the spine, the crab seems to be carrying food about on the tip of its nose! The stored food is consumed when the crab is safe within a retreat, or in times of need.

A Surprising Discovery

The Atlantic spider crab (Libinia emarginata), a temperate relative of the arrow crab, can easily be collected along the eastern coast of the USA. They are inoffensive towards one another and most tank mates, and make interesting aquarium pets.

I still remember my shock upon seeing one wedging kale (provided as food) into the many crevices of its carapace. Eventually, the small crab looked like a walking patch of marine algae…when it ceased moving, its camouflage was perfect (well, nearly perfect…kale doesn’t grow in the sea!).

I later observed spider crabs to pick at and consume bits of their movable garden, so the vegetation serves two purposes (I have not determined if spider crabs will use inedible materials for camouflage, as do decorator crabs and some others). The spider crabs that I have kept gave up this habit upon reaching a carapace size of approximately 4 inches.

The aforementioned crabs are readily available and adjust quite well to aquarium life. I’ll cover their care in detail in future articles. Until then, please write in with your questions and comments. Thanks, Frank Indiviglio.

Further Reading

The diversity of crab species and lifestyles is astounding. To learn about current research in East Asia (where over 1,000 species have been described) and view some remarkable photos, please visit http://www.dbs.nus.edu.sg/biodiversitii/bio/m_crab.html#major.

I have written about the natural history and captive care of crabs and other crustaceans in The Everything Aquarium Book
.

Eileen here. We’ve all heard some of the general “rules of thumb” for stocking an aquarium: an inch of fish per gallon, one fish per gallon, more fish = less aggression and countless others. So, what works best? There are several approaches that can help make stocking an aquarium easier.

Research, research, research!!

It’s no secret that I for one am a big fan of research. I’m not talking in depth taxonomic studies or long term observational studies, just a little planning and reading up on what you would like to keep. We get a lot of questions like “I set up a tank, now what can I put in it?” or “I bought this pretty yellow fish, what can go with it?”. You may be able to save yourself some time, frustration and possibly disappointment by planning out what you might like in your tank before setting it up or buying any fish for it. It also helps you decide what you would like to put in it down the road. That way, you will be able to decorate and filter your tank in the best way for what you’d like to keep and you’ll avoid getting those impulse-buy tankmates that eliminate any chance of having that special fish you’ve had your eye on for months.

Along these same lines, be sure you are aware of the behavior of each item you choose and its requirements. There is nothing worse than bringing a fish home, only to learn that you have to spend more time preparing its food than your own, or finding out that it is a known predator of that favorite fish you already had. A few basic aquarium fish books can help a lot with the basics and can even help you find fish you never even knew existed. You could try shooting us a blog question, email (marinebio@thatpetplace.com) or giving the store a call at 717-299-5691 if you’re looking for help in this regard too.

An inch per gallon? Only sometimes

This is one of the most common stocking “rules” we hear but is often misunderstood and misused. Let’s compare a few common groups of freshwater fish: tetras, goldfish and cichlids. First, the “inch per gallon” or “fish per gallon” rules have to take the adult size of the fish into consideration. Sure a fish might be one inch when you buy it, but if that fish grows into a footlong adult? That changes things. Then, what about the body mass of the fish and the waste it produces? Six little one-inch-long tetras will certainly affect an aquarium different than a six-inch-long goldfish. Goldfish just produce a whole lot more waste, eat a lot more and have a lot more mass and size behind that six-inch-length than all of those little tetras put together. Next, what about the behavior? That same six-inch goldfish is going to have a far different temperament than, say, a six-inch Green Terror cichlid. Two six-inch goldfish could be perfectly happen in a well-filtered 45 gallon aquarium; the two Green Terrors may well try to kill each other. So do we throw out the “inch per gallon” rule altogether? Not necessarily. It is fine to use as a very general and basic guideline for small fish like tetras, danios or livebearers if you take their adult size into consideration, but don’t take it as gospel if you are keeping anything larger.

Zone Defense: It works in sports, it works in aquariums

When stocking your tank, keep in mind that all of the fish won’t be spending all of their time in the same area of the tank. Looking at your aquarium from the front, you can divide it horizontally into 4 zones. The middle two zones are where a lot of fish hang out. In freshwater, this is where you’d find tetras, angelfish, barbs, and some cichlids. In saltwater, this would be your tangs, damsels, clownfish, and some groups of wrasses. The top quarter section is more of the top dwelling fish. In freshwater, these are fish like hatchets, killifish, rasboras, and mollies and in saltwater, this would be some cardinals and dartfish gobies – fish whose mouths are more on the tops of their heads and point upward for those prey items on the surface. The last section, the one on the bottom of the tank, is home to the bottom feeders – catfish, blennies, loaches, and gobies. Some saltwater fish and freshwater cichlids that spend a great deal of their time in and around rockwork also would count towards this group.

Stocking an aquarium with all three sections – top, middle, and bottom – in mind will help you make the most of the space you have. Instead of having a lot of fish that hang out in one of these zones, choosing fish from all three can give you a more complete look to your tank and can help spread out the activity and aggression throughout the whole tank.

The more, the merrier? Or one big spotlight?

There are two big ways to plan an aquarium – having an active tank with lots of activity and schools of little fish, or have a showcase item like a big saltwater angelfish or showing cichlid and build the rest of the tank around it. Both can be stunning in their own way but take some planning. Having a tank full of different schools of little fish can be interesting and active. You can have a higher number of fish this way but there isn’t one big thing to focus on. Or, you can have one big fish like a Discus and complement it with just a few other little fish for some subtle activity and to help with clean-up. Some of the most interesting tanks can be species-only tanks. These tanks have just one kind of fish like an aggressive cichlid or a saltwater oddity like a frogfish, and nothing else. These are the true “pet fish”. They can be fascinating but aren’t as diverse as community aquariums.

Biotopes – a little piece of nature.

Some of my favorite aquarium have been biotopes. These are tiny pieces of a specific environment where everything in the aquarium is designed and chosen around that location or habitat. For examples, a Caribbean biotopes would have only fish and invertebrates chosen from the Caribbean, so a fish from the Indo-Pacific would not be chosen for this tank. This is how most public aquariums are designed and is one of the more collector’s approaches to aquariums. Instead of relying on the impulse buy, this method is all about planning and choosing the perfect addition for your little slice of nature. Much better than a postcard for remembering that trip to Hawaii!

These are just a few approaches to choosing the next addition to your favorite aquarium. Feel free to share your own and never be afraid to ask if you aren’t sure if what you want is right for you!

Hello, Frank Indiviglio here.  I have always included insects in the diets of a great many fishes, including shallow-water marine species (in the accompanying photo, you can see a number of typical community aquarium species swarming around a cricket).  Please see Part I of this article for further information on the role of insects in marine and fresh water fish diets.

My Experience with Wild Fishes

Whenever I have the opportunity, I toss insects into natural water bodies.  Time after time, be I near a quiet pond in Ohio or a salt marsh on Long Island, the insects never last more than a few minutes before being consumed by resident fishes.  Eventually, I came to believe that terrestrial invertebrates play a great role in the diets of numerous freshwater, brackish and even marine fishes (many insects fly far out over the ocean, especially on migrations, or are carried there by the wind).

Current Research

Just this month (August, 2009), biologists at the National Oceanographic and Atmospheric Administration published the results of a research effort which addressed this very topic.  Surveys of fishes in lakes across North America have revealed that terrestrial insects comprise up to 100% of the diets of some fish species (my own casual observations are rarely validated in such a timely fashion!). 

However, in lakes where development has eliminated shoreline vegetation, insects typically make up only 2% of the diets of the same fish species.  The importance of insects is evidenced by the fact that fishes living in lakes with developed shorelines take in 50% less energy on a daily basis and grow slower than those in undeveloped lakes.  Fortunately, re-planting even a narrow fringe of bushes and grasses along a lake can dramatically increase terrestrial insect populations.

Canned Insects for Aquarium Fishes

Both live and canned insects are eagerly accepted by many typical (and untypical!) aquarium fishes. Canned invertebrates may be better suited for most aquarists, who, unlike their reptile-keeping colleagues, are not often in the habit of maintaining live insect colonies. What’s more, they retain all the nutrition of live insects but are far more convenient to store and use.

Canned grasshoppers and adult crickets are ideal for large carnivorous fishes such as Oscars and other Cichlids, arowanas and many catfishes, and can also be crushed or chopped for smaller species.  Other varieties of canned invertebrates include snails, mealworms, silkworms and young crickets . Freshwater shrimp , also available in cans, are eagerly taken by a wide array of fishes. 

Further Reading

In some habitats, the availability of “junk food” is reducing the role of insects in fish diets.  To learn more, please see http://www.sciencedaily.com/releases/2004/09/040928101517.htm.

Please write in with your questions and comments.  Thanks, until next time, Frank Indiviglio.

Ah, Friday. Best day of the week! Though there is never a lack of interesting fish/aquarium/ocean related news to reinvigorate us and carry us through. Let’s take a look at the news and newbies!

The Grunion are running! AHHHHH! Actually, if you don’t know what grunion are and you’re concerned about why they are running, don’t worry, it’s actually a good thing. This might be something I would put on my bucket list of things to experience before I die. (I’m easily amused.) http://www.al.com/newsflash/index.ssf?/base/national-19/1250767015290200.xml&storylist=national&thispage=1

If anything could be more exciting than the running of the grunion, check out the image captured by Google earth!!! I always knew she was there somewhere, not even Nessie can escape the spying eyes in the sky! http://www.guardian.co.uk/theguardian/2009/aug/27/loch-ness-monster-google-earth

Everybody has an opinion on goldfish in the aquarium world, and sadly, the opinions are not always good. But when you see those bulging eyes and that bobbing, bulbous body, its hard not to smile. In case you didn’t know already goldfish do have some redeeming qualities, and they may be cause to consider them again as a new family pet. http://www.dailymail.co.uk/news/article-1209316/Gulp-Why-life-goldfish-bowl-lot-exciting-thought.html

We get questions all the time from customers about something that emerged from their live rock or from a coral or from seemingly nowhere. Strange worms are often a fact of life in reef aquaria, and though you may not always see them, chances are there are some hiding away in the dim recesses of your rock. This little gem might help you ID or at least get closer to IDing the little surprises that come along with reefing.

New and exciting this week at TFP:

Check the blog for pics of these guys.

We got a Cave Bass this week! These guys aren’t available often but they are super neat. They’ll tend to hide out in shadowy caves in your tank, but you’ll be pleased just to know he’s there.

Hello, Frank Indiviglio here. I have always favored fishes that seem to straddle the line between the fish and reptile/amphibian kingdoms. Included among these are both marine and freshwater forms, including the toadfish, frogfish, lizardfish, lungfish, mudskipper (note the common names!) and others. The freshwater fish family Polypteridae, containing the bichirs and the reed or rope fish, has long fascinated me and seems very popular with visitors to the exhibits I have worked on at the Maritime Aquarium (Norwalk, CT) and the Bronx Zoo.

Few if any bichirs have been well-studied, and even the most commonly available species are rarely bred in captivity; much can be learned by the patient aquarist.

Description

The dorsal fin rays of these elongated, snake-like fishes are separated from one another, rising and falling in a series of humps and lending them the appearance of scaled-down dragons. This effect is most evident in the aptly named Senegal dragonfish (please see below). The pectoral fins are rimmed with fleshy lobes, and are paddle-like in shape and function.

Swimming takes the form of short bursts, but mainly these fish scull along the bottom. The largest, including the commonly sold reedfish, can reach 3 ½ feet in length, but most are considerably smaller. Although dissimilar externally, bichirs are believed related to sturgeons, paddlefishes and gars.

Range and Habitat

Bichirs are limited in range to tropical Africa and the Nile River system, and are usually associated with shallow, plant-choked waters such as marshes, swamps and the shores of slow-moving rivers.

Future Amphibians?

The amphibian-like qualities of the bichirs are not limited to appearance alone. The swim bladder has evolved into an accessory breathing organ, allowing them to breathe atmospheric oxygen and to survive out of water for some time…few species are rumored to voluntarily leave the water for short periods. The young of some species even sport external gills, much like salamander larvae!

Reed or Rope Fish, Erpetoichelys calabaricus

This brown West African native has a sinuous, snake-like body and a wide mouth. The reedfish hides under the mud by day, emerging at night to feed upon insects, fishes, worms and frogs. It can reach a length of 3 ½ feet, but rarely attains that in captivity.

Senegal Dragonfish or Cuvier’s Bichir, Polypterus senegalus

Rounded, widely-separated dorsal fin rays lend the Senegal dragonfish an uncanny resemblance to its mythical namesake…it really does look like a miniature dragon!

Senegal dragonfishes are distributed throughout the Congo Basin and reach 12 inches in length. They make hardy, interesting aquarium pets and often learn to anticipate feeding times. The effect of a large specimen in a well-planted aquarium is quite spectacular – they definitely deserve more attention from aquarists.

Ornate Bichir, Polypterus ornatipinnis

Swamps and marshes in West Africa are the home of this commonly imported bichir. Patterned with a lacework of black markings, the ornate bichir is one of the more attractive members of its family.

Unfortunately, due to its unique appearance, the ornate bichir is often purchased on a whim. Few realize that the youngsters sold in pet stores eventually grow to 18 inches in length, and are often aggressive towards tank mates. However, properly accommodated ornate bichirs make fascinating pets, and, as they are rarely bred in captivity, are ideal species to study.

Further Reading

You can read more about bichirs, and see a list of all recognized species, at http://www.fishbase.com/NomenClature/ScientificNameSearchList.php?crit1_fieldname=SYNONYMS.SynGenus&crit1_fieldtype=CHAR&crit1_operator=EQUAL&crit1_value=polypterus&crit2_fieldname=SYNONYMS.SynSpecies&crit2_fieldtype=CHAR&crit2_operator=contains&crit2_value=&group=summary&backstep=-2.

I’ll address captive care in more detail in the future. Until then, please write in with your questions and comments. Thanks, until next time, Frank Indiviglio.

Polypterus senegalus image referenced from Wikipedia and originally posted by Zhyla

Rope fish image referenced from Wikipedia and originally posted by Michael Zalewski