That Fish Blog – Aquarium Advice and Information

Surprising new information about aquatic invertebrates is uncovered every day…the following is a small sample, which I’ll add to from time to time.  Please see Part I of this article as well.

Good and Bad Pets

The venom of the tiny blue-ringed octopus, Hapalochlaena maculosa, is one of the most toxic known, with the amount delivered in a single bite being sufficient to kill an adult person.  Yet this creature occasionally appears for sale in the pet trade – learn to identify and avoid it!

Giant water bugs (Family Belostomatidae) can be collected throughout the USA and make interesting, if aggressive (they can inflict a painful bite), aquarium subjects. The males of many species carry the eggs about on their backs.  A species I collected in Venezuela topped 4 inches in length, and regularly consumed small frogs.  Another I came across at Japan’s Kaiyukan Aquarium easily subdued a 3 inch long minnow.  Please look for my future article on aquatic insects.

Most corals rely upon minute creatures for their food and are difficult to maintain in aquariums.  However, tooth coral (Cynarina spp.) accept pieces of shrimp and other large food items, and should be considered as a first choice by those new to coral-keeping.

Jellyfishes are not usually available in the pet trade, and are quite delicate in captivity.  One exception is the upside-down jellyfish, Cassiopeia andromeda.  In contrast to all others, it rarely swims but rather rests in a “head down” position, with the tentacles trailing above.  Given intense lighting (it relies upon symbiotic algae) and plenty of brine shrimp, it often thrives in the aquarium.

Catching and Storing Food

Surprisingly, some spiders have adopted an aquatic lifestyle, and several of these adapt well to aquarium life. North America’s fishing spiders, Dolomedes spp., float on the water’s surface and dangle a leg below to lure small fish within reach.  The European diving bell spider, Argyroneta aquatica, takes aquatic life a step further – it lives in a submerged, air-filled retreat from which it launches attacks on passing fish and invertebrates.  Please look for my future article on these unusual creatures.

Several crabs have interesting ways of “planning for the future”.  Atlantic spider crabs, Libinia emarginata, stuff marine algae into crevices on their shells, effectively camouflaging themselves and storing food at the same time (those I have kept abandon this habit when they reach 3 inches in size).  The ever-popular arrow crab, Sterorhynchus seticornis, impales bits of food, to be consumed in the future, on the pointed end of its carapace.

How Big…How Old?

Crabs, lobsters and their relatives (Order Decapoda) are among the most important aquarium and food-trade invertebrates.  The legs of the Japanese spider crab, Macrocheira kaempferi, the largest of the group, may span 13 feet.  Both it and the American lobster, Homarus americanus (at 60+ pounds, the heaviest Decapod) may live for 100 years. The largest freshwater species is the 9 pound New Zealand crayfish, Astacopsis gouldi.

At 4.5 feet across and up to 750 pounds in weight, the South Pacific’s giant clam, Tridacna gigas, is the largest of the world’s 6,000+ bivalves (clams, oysters and relatives).  It relies upon commensal green algae for much of its food, and produces the world’s largest pearls – one of which weighed in at 14 pounds!

Many mollusks (snails, clams and their relatives) lay down growth rings, which appear as irregularly-spaced lines on the shell.  Much as with trees and turtles, these lines can often be used to determine these creatures’ ages.

Defense and Survival

Although largely aquatic, several species of North American crayfish, known as chimney crayfish, exploit terrestrial habitats.  They live in wet meadows and dig tunnels, which may exceed 10 feet in length, to the water table.  Recently, it was discovered that these water-filled retreats provide vital breeding sites for salamanders during droughts.

Sea urchins are interesting aquarium inhabitants, but most aquarists find them rather unresponsive.  However, they react immediately to the shadow thrown by a hand or other object passing overhead by orienting their spines towards the disturbance.  This is a defensive reaction, designed to direct the sharp spines towards an oncoming fish or other predator.

I look forward to hearing about your own observations concerning aquatic invertebrates, and to answering your questions.  Thanks…until next time, Frank.

A great deal of interesting information concerning marine, fresh water and terrestrial in invertebrates of the Pacific Basin is available at the following web site:

http://pbin.nbii.gov/marinverts/index.asp

Knowing where to start and stop when it comes to writing about invertebrates is a real problem – any single group could keep one occupied for a lifetime. Today I’d like to highlight some interesting facts concerning a few commonly kept types and their relatives. I’ll add to this from time to time.

General
Invertebrates (animals without backbones) account for approximately 97% of the world’s animal species, yet we have no idea of their total numbers. The smallest are invisible to the naked eye while the largest, giant squid, may exceed 60 feet in length.

Nearly every injectable drug manufactured in the USA is tested for bacterial contamination with a chemical extracted from horseshoe crab blood (synthetics do not work as well). Several states are restricting the collection of these animals (often used as fertilizer!) and requiring that they be released after blood specimens are taken.

Invertebrates have colonized every habitat imaginable, from freezing Antarctic seas to the boiling hot water of geysers. The sponges, crabs, tubeworms and others living near deep sea vents form the only animal community that does not rely upon photosynthesis as the basis of the food chain (bacteria that consume methane function as “plants”).

Despite being a creature of legend for centuries, the giant squid, Architeuthis sp., was not captured on film until 2004. Two years later, the same Japanese scientists that filmed the animal caught a specimen on a fishing line, thus giving the world its first view of a living giant squid.

Eating and Being Eaten
Despite radically different appearances, jellyfishes, sea anemones and corals are closely related (Phylum Cnideria). All gather food and excrete wastes through a common opening, and overcome their prey with stinging cells.

Jellyfish, although comprised largely (95%) of water, are able to snare prey as large as small fishes. Surprisingly, they form the bulk of the diet of many huge sea creatures, including the world’s biggest turtle, the leatherback.

The dried krill (shrimp-like creatures of the Class Brachiopoda) that you may use as fish food form the basis of the food chain in most of the world’s oceans. Also, a number of surprisingly large creatures, including whales, manta rays and basking sharks, rely upon krill as their primary diet, consuming billions each day.

Although viewed by most as sluggish creatures, many of the world’s 70,000+ species of snails and slugs (Phylum Mollusca) are quite effective predators. Various types pry open or drill through clam shells and cone snails impale fish by shooting out barbed tongues. Certain sea slugs consume anemones and incorporate the stinging cells into their own gill tufts.

Reproduction
Australia’s Great Barrier Reef, the world’s largest, is 1,250 miles long. Somehow, its untold billions of individual coral animals synchronize reproduction so that the sperm and eggs of all are released into the sea at the same time.

Banded coral shrimps, Stenopus hispidus, form long-term pair bonds, and males have been observed to share food with gravid (pregnant) females. The eggs, which are glued to the females’ swimmerets (feathery structures below her abdomen), are aerated and protected by her. Upon hatching, however, the young may be consumed by both parents!

Surviving
Sea cucumbers make interesting if occasionally unsettling aquarium inhabitants – when disturbed, they discharge their stomachs through the anus! Amazingly, these sea star relatives can regenerate the discarded stomach.

The unique tube feet of sea stars (Phylum Echinodermata) function in locomotion, respiration and as sensory organs. Water-filled canals linking the feet can, via a series of valves, build up enough pressure to enable sea stars to pry open clam shells (try that with your hands!).

The anemone hermit crab, Parurus prideauxi, places a stinging sea anemone on its shell as protection and camouflage and re-locates it when changing shells. The anemone, in turn, gets a safe anchoring place and, perhaps, access to leftovers from the crab’s meals.

Using Invertebrates – Now and Then
Over 10,000 species of sponges (Phylum Porifora) inhabit both fresh and salt water. Several types have been collected from the Mediterranean Sea since ancient times. After drying in the sun, their fibrous structural tissue (spongin) made an excellent bath sponge.

Horseshoe crabs (Phylum Chelicerata) are among the world’s most ancient creatures and have remained relatively unchanged for over 300 million years. Closely related to spiders and not crabs at all, small specimens make interesting additions to a marine aquarium.

And, Finally…An Odd Personal Tale
Octopuses (Class Cephalopoda) are the most intelligent of the invertebrates and make fascinating aquarium subjects. They are also quite well-sighted – one I kept would, according to my grandmother, “stare” at her while she worked in the kitchen. Not wishing to upset my beloved pet, she covered its tank when preparing octopus for dinner!

Well, only a few billion more facts to go! I’ll continue next week, and periodically after that. As there are so many possibilities, I would greatly appreciate your suggestions concerning invertebrate-oriented subjects that you may wish to learn more about. Thanks, until next time, Frank.

You can learn a great deal about invertebrate biology at the web site of the Australian Museum:
http://www.amonline.net.au/invertebrates/ara/index.htm