The Asian Shore Crab: Introduced Pest as Aquarium Animal and Food Source

Asian Shore CrabsIn 1988 a small crab showed up on the New Jersey shore, apparently discharged there along with bilge water from ships that had visited the Western Pacific.  Deceptively innocuous, by the mid 1990’s the Asian shore crab (Hemigrapsus sanguineus) was the dominant inter-tidal crab in an area stretching from Maine to North Carolina. In the space of 3-5 years, it became the most common crab at several estuaries that I visit…at one, hermit crabs and sand shrimp have virtually disappeared.

Asian shore crabs seem to co-exist more peaceably with one another than do native species…those pictured here were found under a single small rock.  I wonder if, in contrast to other crabs, newly-molted individuals are not attacked by neighbors. 

Making the Most of an Invader

There is, however, a silver lining to this environmental cloud…the crabs make a nutritious addition to the diets of many aquarium fishes and invertebrates.  Many fishes consume small crabs whole, and they can be broken up for smaller fishes.  Freshwater fishes ranging in size from guppies to peacock bass will enjoy an occasional crab meal as well.

Shore crabs thrive for weeks in damp seaweed under refrigeration and can be frozen for future use.

Collecting Crabs and other Marine Animals

Inshore Lizard FishAsian shore crabs inhabit tide-pools, jetties and salt marshes.  They forage as the tide recedes and are most easily collected at low tide, when they shelter below rocks and other cover.  A wide variety of sizes (please see photo), suitable for nearly any size aquatic pet, can be gathered in no time at all.

While searching for shore crabs, keep your eyes open for shrimps, worms, mussels and other small creatures.  All are useful aquarium foods, and many make very interesting display animals (shore crabs are unprotected, but check local regulations regarding others).

An Unusual Visitor from the South

Seining and setting out minnow traps will improve your catch, and the sea never fails to provide wonderful surprises.  Last summer an inshore lizardfish (Synodus foetens) showed up in my net (please see photo).  I’ve had only limited success with them in captivity and so released this one after taking some photos.

Shore Crabs in the Aquarium

As is my way, I tried my hand at keeping Asian shore crabs in captivity, and was pleasantly surprised.  Although in nature foraging is tied to the tidal cycle, captives abandon this strategy and soon appear at all hours (in contrast, native fiddler crabs that I have kept became active according to an internal clock – feeding and retiring in groups, despite the absence of a tidal influence).  Shore crabs feed ravenously on any and all plant or animal based fish foods.

I set up a group in a large estuary exhibit at the Brooklyn Children’s Museum, and they have done quite well there.  The crabs forage underwater and on rocks protruding above the surface, and co-exist with sand shrimp, striped killifish and other natives (in a small aquarium, they should be monitored closely for aggression).

Crab Alternatives

Please check out our extensive selection of frozen and freeze-dried  fish foods.  Many contain whole marine animals, and are an excellent addition to the diets of aquarium fishes and invertebrates.

Further Reading

Information about this and other introduced marine animals and plants is posted at http://www.seagrant.uconn.edu/INVID.HTM.

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

Koi: To Feed or Not to Feed and A Matter of Extremes in the Spring

Anyone who keeps a koi pond in cooler temperatures has been there. You start getting a few warmer days in late March and your koi, who had been inactive all winter, begin to swim around and look for food. Being the “good” koi keeper you are, and just an all around nice person, you start feeding your hungry friends almost immediately. The feeding continues to increase, while your pond continues to get greener. Meanwhile the local garden store is getting in a load of excellent looking Asagi or Shiro Utsuri Koi direct from Japan next week, and though you already have a questionable number of little Koi in your 1000 gallon pond, one more couldn’t hurt, right?

Pond keepers are creatures of extremes and it’s nothing we’re ready to apologize for (I mean, koi are soooo cool!). But, from a biological balance perspective, it’s really easy to start tipping the scale in your pond in favor of algae and unfavorable health conditions, particularly in the cooler weather.  

Believe it or not, koi in an outdoor pond do not have to be fed to survive. Being the scavengers that they are, they’ll have no trouble finding the nutrients they need among the detritus, bugs, and general wild things that end up in your pond throughout the season. What this means to you is everything you add to the pond, whether it be more fish, fish food or plants, adds to the nutrient load. In early spring, this nutrient load is particularly important for several reasons. First, your beneficial bacteria are not yet running full steam. This means ammonia takes that much longer to break down. When you combine that with the fact that your fish, and their immune systems, are still in slow motion due to the cooler water temperatures, a high nutrient load can cause problems. In addition, the natural “nutrient sucker-uppers,” your aquatic plants, are also struggling to gain a hold for the new season, so that part of your natural filtration is crippled as well.

Many koi keepers than ask, how can I get around this problem? I love my pond and I’m not going to stop feeding my koi, and I’ll probably add more fish to the nutrient load from time to time because they’re too awesome to pass up. Our response to you: avoid the extremes. Be sure to have the necessary test kits on hand to make sure levels remain nominal throughout the season. If you start to see problems, just like in an aquarium, try a water change, or add some bottled bacteria to help the chemistry settle. If your pond starts to get cloudy or full of algae, try adding more plants, or cutting back a few feedings. If you’ve tried all of these solutions and the problems are not going away, it may be time to consider a larger filter system or (gasp!) trimming your koi stock a little.

Good luck with your pond this season!

An Aquarist’s Glossary of Terms

Hi, Eileen here. There are a lot of different terms and phrases, used in reference to saltwater and freshwater aquariums alike, that may be unfamiliar to some aquarists or that you might come across in books, magazines or your local fish store like That Fish Place/ That Pet Place. I thought it might be beneficial to place a glossary of common terms as a reference. Here are some of the most common terms used in the aquarium trade that may be confusing to someone just starting out or beginning to explore the hobby. Keep in mind that they may have different meanings or may be used differently depending on the region or the aquarist you may be speaking to.

Biological terms:

  • Barbel: the “whiskers” or whisker-like appendages around the face and mouth of some fish.
  • Benthic: Benthic organisms live on, in, or attached to the bottom. These organisms include corals, crabs, starfish, cucumbers and worms.
  • Breeding styles: There are several different breeding styles common in aquarium fish and invertebrates.
    • Livebearer: Livebearers give birth to live young that are fully or nearly fully formed and often resemble miniature adults. Guppies, swordtails and seahorses are a few well-known livebearers.
    • Mouthbrooder: Mouthbrooders hold their eggs and eventually their young in their mouths until the young are ready to live on their own. The parent holding the young often does not eat during this time. Some cichlids and saltwater cardinalfish are mouthbrooders.
    • Egglayer: This is the breeding style that most people are familiar with. The female fish will lay a clutch of eggs and the male will fertilize the eggs after they are released. Most parents will guard their eggs during this time. Freshwater angelfish and saltwater clownfish are common egg-layers.
    • Eggscatterer: Egg-scatterers show little to no parental care for their young and will randomly scatterer the eggs across the substrate or vegetation. They often may eat their eggs and fry if not removed from the site. Tetras, danios, and rasboras are all egg-scatterers.
    • Bubblenesting: Gouramis and bettas are well-known bubble-nesters. The male will build a ring or nest of bubbles at the surface of the tank or plants and will defend other fish, including the female who laid the eggs, from getting close to the next.
    • Eggburying: Annual fish like killifish will bury their eggs in muddy substrate in the wild where they remain dormant throughout the dry season and until the next rainy season. These fish are typically short-lived and only have a lifespan of one or two seasons.
  • Cichlid: Cichlids (pronounced SICK-lids) are a group of fish known for being some of the most aggressive and territorial. They are native to distinct regions and many species have limited range. Cichlids are generally divided into “Old World” and “New World” groups.
    • Old World Cichlids: These cichlids are those found generally in the eastern hemisphere, most notably the African Cichlids found in the African Rift Lakes Lake Malawi, Lake Tanganyika and Lake Victoria basin. This group also includes West African, Madagascar and Asian cichlids. These are typically found in very specific water conditions and should not usually be mixed with other more docile tropical fish.
    • New World Cichlids: These are also collectively referred to as South and Central American cichlids but may also include some found in southern North America. Many are large and aggressive, but there are also dwarf species and some that are rather docile.
  • Coral: Coral refers to a very large group of invertebrates in the family Cnidaria. They are very widespread in appearance, habitat, requirements and lifestyle, but are only found in saltwater environments. This group can further be dividing into LPS, SPS, and Soft Corals.
    • Large Polyp Stony Corals (LPS): These corals have hard skeletons covered with fleshy tissue that often can make the coral look like a plant or anemone. These corals are found in a variety of environments and are often not as sensitive as their SPS cousins. They feed through a combination of photosynthesis from algae in their tissue and filter feeding from the water column. This is not technically a scientific classification, but is used by hobbyists as a convenient way of dividing corals.
    • Small Polyp Stony Corals (SPS): These corals have a more rigid appearance with very small polyps or thin tissue covering their skeletons. They live primarily on reefs and most get the majority of their nutrition from the algae in their tissue. These corals are very popular amongst hobbyists for propogation and “fragging”. Again, like LPS corals, this is not an official scientific classification.
    • Soft Corals: Also known as leather corals, the vast majority of these do not have a rigid skeleton, though there are a few exceptions, like Heliopora. They filter-feed or absorb most of their nutrition from the water and can live in a wide range of water conditions.
  • Crustaceans: Crustaceans are a group of invertebrates characterized by their insect-like appearance, hard exoskeleton that they must “molt” or shed to grow, and segmented bodies. Common aquarium crustaceans are shrimp, crabs and lobsters.
  • Cyanobacteria: Cyanobacteria (“cyano” or “slime algae”) is a bacteria commonly mistaken for algae and can be green, brown, red, black or blue. It is considered an aquarium nuisance and usually will bloom when water quality or lighting is poor. It is most common in saltwater aquariums, but can also be found in freshwater aquariums at times.
  • Diet: Diet refers to what an animal will normally eat in the wild. Five main diet or feeding types are common in aquarium:
    • Herbivore: Herbivores eat plants and plant matter almost exclusively.
    • Carnivore: Carnivores are meat-eaters and feed on very little plant matter.
    • Omnivore: Omnivores eat both plants and animals in their nature diet. Some may eat more plants than meat or vice versa.
    • Planktivore: Plantkivores feed on very small plants and animals in the water column. They may actively search out this food or may filter feed by sifting through the water column and feeding on whatever they find there.
  • Photosynthesis: Some invertebrates have algae known as zooxanthallae living in their tissue which produces proteins through photosynthesis. The animal then feeds off of the by-product of these symbiotic algae.
    • Diurnal: Diurnal organisms are active primarily during the day or in daylight.
  • Fin types: Each fin and body region on a fish is named and the common or scientific name of the fish may refer to markings on or around these fins. Knowing the names of the fins can also help in identifying fish or diseases. Not all of these fins are found on every fish and there are several other minor fins found in some groups.
    • Dorsal: The dorsal fin runs along the back and spine of the fish. The dorsal side of the fish also refers to this top half or the region around its back. This fin is used to help stabilize the fish while swimming.
    • Pectoral: Pectoral refers to the chest of the fish or the fins on either side of the body just behind the gills. These fins are used mostly in steering the fish, but also help to propel it through the water.
    • Peduncal: The peduncal or caudal peduncle is the narrow area between the main body of the fish and the tail.
    • Pelvic: Pelvic fins are paired and are found under the pectoral fins on the lower part or “belly” of the fish. They are used to help stop or turn the fish and to move vertically through the water column. Some fish like gobies have fused pelvic fins that act like a suction cup and help fix the fish onto a surface.
    • Anal: This fin is located on the bottom of the fish just in front of the tail. It is also used to help stabilize the fish. In male livebearers, this fin is modified into the pointed gonopodium and is used to fertilize the female.
  • Invertebrate: An invertebrate is any animal without a backbone. This group includes snails, shrimp, crabs, corals, octopuses, clams, starfish, urchins and many more animals.
  • Lateral Line: The Lateral Line is a sensory organ found primarily in fish. The Lateral Line can be seen as a groove running the length of the body on most fish and is used to detect movement in the water, even from great distances. Schooling behaviors and the quick movement and reflexes seen in some fish are thought to be related to this organ. Some fish can be identified by markings around the Lateral Line and some diseases like Head and Lateral Line Erosion (HLLE) are associated with it as well.
  • Nematocyst: Nematocysts are stinging cells found in the invertebrate phylum Cnidaria (anemones, jellyfish, corals and other invertebrates). The cell is “spring-loaded” – when the trigger is activated, the cell springs open and injects a harpoon-like projection into the target. This is a defense in most animals but some fish like jellyfish use this as a passive way to catch and disable their prey.
  • Nocturnal: Nocturnal organisms are active primarily at night.
  • Operculum: Operculum is Latin for “little lid”. In fish, this is the bony plate that covers the gills. In snails, this is the hard trapdoor that protects that snail when it retracts into its shell.
  • Plankton: Plankton and planktonic organisms do not swim against the flow of the water but rather travel with the flow. Most plankton is very tiny and is a primary food of filter-feeding organisms like corals and feather dusters, but other planktonic organisms like jellyfish and even the very large Ocean Sunfish can be much larger in size.
  • Photoperiod: The photoperiod is the length of day and night an organisms is exposed to and their reaction to it. An improper photoperiod can affect the health and activity of aquarium fish, invertebrates and plants.
  • Photosynthesis: Photosynthesis is the process by which a plant (including algae) uses carbon dioxide and sunlight to produce organics like sugars and gives off oxygen as a by-product. Some bacteria like cyanobacteria also use photosynthesis.
  • Scales: Most fish are covered with rigid scales for protection. These scales vary with the type of fish. Fish like sharks have scales also known as “dermal denticles” for their tooth-like structure. Other fish have scales with either a smooth outer edge (cycloid), or scales with a serrated edge (ctenoid).
  • Scientific name: The scientific name of an organism is the name assigned to it by scientists and taxonomists to be used as the “official” and universal name for that organism. In contrast, the common name can vary between countries, languages, regions and from aquarist to aquarists. Scientific names are typically written in italics while common names are often written with quotation marks.
  • Sexual Dimorphism: Sexually dimorphic animals have physical characteristics that differentiate between males and females of the same species. The difference can be subtle (a specific marking or size difference) or very obvious (completely different coloration).
  • Venomous: A venomous organism injects a toxin into its prey, either as a defense or as a way to disable their prey. This differs from poisonous organisms whose toxin must be ingested or absorbed.
  • Zooxanthallae: These tiny algae cells live within the tissue of other organisms like corals and anemones. The larger animals or colony provides the zooxanthallae with a host and the zooxanthallae provides the host animal with energy from photosynthesis. A coral may “bleach” or eject all of the zooxanthallae from its tissue if stressed, often resulting in the death of the coral.

I’ll be back with some other terms that may be useful for those who are new to the hobby in future posts!

Synodontis Catfish for the African Cichlid Tank

Jason here. Working at That Fish Place, I have many people ask me about bottom feeders that they can put into a tank with their African Cichlids.  Since cichlids tend to be aggressive, it can be difficult to find suitable tankmates.  A great solution to this problem is adding a Synodontis catfish species. 

There are many species of Synodontis that grow to various sizes.  Synodontis are great because they are often found in many of the same locations as the cichlids. One of my personal favorites is Synodontis petricola, often referred to as Pygmy Synodontis among hobbyists.  They are a relatively small, in comparison to the other members of the genus, maxing out at around five inches.  This catfish is native to Lake Tanganyika, in Africa, which is part of the group of lakes commonly referred to as the African Rift Lakes and has a pH ranging from 7.0-8.5.  Their coloration is usually brown with black spots.  Their fins are black with highly defined white trim.  Dietary choices consist mostly of meaty foods, but they will also pick at algae from time to time.

Another excellent choice for those with an Afican cichlid tank is Synodontis multipunctata, also from Lake Tanganyika.  In their natural environment, their preferred pH ranges from 7.8 – 8.5.  They have a similar appearance to the Pygmy Synodontis, only with less defined white trim on the fins and a larger max size, as in the aquarium they grow to approximately 8 inches in length.  They prefer tanks with a lot of dark places to hide out.  Like the petricola, they are omnivorous and are known to pick at algae along with their main diet of meaty foods.  They can usually be found under the common name Cuckoo Synodontis, though petricola also shares that common name.

Our most commonly sold Synodontis is a tropical species that tends to swim upside down.  It gets its common name, Upside-Down Synodontis Catfish because of this odd style of swimming.  Its scientific name is Synodontis nigriventris.  Unlike the prior two catfish noted, this one won’t do as well in with the African Cichlids, but makes an excellent addition to tanks with a lower pH, ranging from 6.0 – 7.5.  Full grown they will only reach about 4 inches, and they are active and interesting to observe.  They can be kept with most tropical fish, but they have been known to cause some problems with the smaller tetras.

There are many other many possibilities, when looking for an interesting bottom dwelling species to add to your home aquarium.  There are many different colors and sizes.  Come in to see us or drop us an e-mail at Marinebio@thatpetplace.com if you need any help or advice in choosing a species.

Caribbean Fish and the Gulf Stream

Cory here. The invasion of the Volitan Lionfish (Pterois volitans) has many concerned for the future of fish populations in the Caribbean and off the waters of Florida. The lionfish are swallowing native baby fish at an incredible rate, leading experts to believe this will begin to thin fish populations. Along with commercial fishing, the future is beginning to look bleak. The lionfish have spread throughout the eastern waters of Florida and are even being found along the shore of New York and Long Island. Wreck divers off of the North and South Carolina waters are finding an abundance of Lionfish. How can this be, a warm water fish in the cold waters of the Mid Atlantic and New England Coasts?

The answer is the Gulf Stream. The Gulf Stream is a current that starts in the Gulf of Mexico, flowing around Florida and up the East Coast of the United States. The current begins to flow further off shore of New England, passing the Southeastern shores of Newfoundland and out into the Atlantic Ocean. The current transports warm water from the Caribbean, the whole way to Europe. The Gulf Stream has a large impact on coastal temperatures not only along the east coast, but in Europe.  Along with the warm water are tropical fish, which also make the trip along the Atlantic coastline.

There have been Spot-fin Butterflies (Chaetodon ocellatus), juvenile Blue Angels (Holacanthus bermudensis), and even small Barracuda spotted by divers off the coast of Rhode Island. In the north, during the fall, divers and snorkelers go in search for tropical species for personal and public aquariums. The sad part of this all is tropical fish caught in the stream will inevitably die as they are carried into cooler waters. Some of the best fishing from North Carolina and northward can be found off shore in the Gulf Stream where water temperatures can be close to 20 degrees higher just 150 to 200 miles offshore. Here Tuna, Wahoo, and Mahi can be found throughout most of the year. The clarity is just as amazing as the temperature difference, going from no visibility to over 100 feet in just 50 miles or so.

Typically, large or adult specimens are not found far from their native waters, because they can swim against the current, which averages around 4 MPH. Normally, juvenile fish or larvae are found due to immaturity, or the inability to fight the push of the current. The biggest question yet is how do these fish make it to the coastal waters of New England, which is 200 to 400 miles away from the Gulf Stream? The logical reasoning at this point is that they are carried toward the coast in small warm water eddies that break off the main current.  Otherwise, the juvenile fish would have to swim hundreds a miles away from warm water into the colder water to only die a month or two later.