Well, its actually not that hard to keep some of our native (temperate) marine fishes and inverts in an aquarium, as long as you keep a few basic rules in mind:
1. Know what species youve collected.
2. Avoid fishes that will outgrow your tank.
3. Avoid fishes that live in deeper, colder waters.
4. Check your local Fish & Wildlife regulations (dont take any fish that are below the legal size for that species).
5. Follow good aquarium keeping regular water changes, etc.
I find that many of our native marine fishes are actually easier to keep than some of their tropical cousins.
Tanks for these fishes can be as small as a 10 or 20 gallon for a few small fish and hermit crabs, while a 55 gallon tank (or larger) would be a good choice for a greater variety of fishes.
As with most aquaria, filtration can be as simple or complex as you like, as long as you have biological, mechanical, and chemical filtration of some sort I have kept many of these tanks with simple sponge filters and a small powerfilter. Currently I am using some of the methods that have become popular with reef aquaria -- a deep sand bed, native rock ("liverock") and a venturi protein skimmer. I do find that my latest tank requires less frequent maintenance, and the sand bed is allowing some interesting fauna to thrive.
The biggest difference in keeping temperate marines is that they require much lower temperatures than tropical fishes. In fact, deepwater species would require temperatures of around 50 degrees (F), which would necessitate a chiller and possibly a double-paned aquarium (to prevent condensation).
Because of that, I prefer to keep coastal species, which I collect in less than 10 feet of water. The coastal species are much more tolerant of variations in temperature, salinity, and water quality than the deeper water species. However, it is still important to keep the temperature lower than for tropical species. I find a cool (unheated) unfinished basement works well. If you do not have access to an unheated basement you may want to purchase a chiller, or at the very least an air-conditioning unit.
I feed a variety of foods, tailored to the needs of the fish and inverts I am keeping. I rely on Omega One brand First Flake as a staple food, as it is high in fats and fatty acids needed by marine fishes (and it is the first flake food my native fish consistently accepted) and contains vitamins that frozen and live foods may lack. I also use a variety of spirulina enriched flake foods as needed. I feed a variety of frozen foods, including mysid shrimp, pacific plankton, spirulina-enriched brine shrimp, and bloodworms. (I try to limit the amount of non-marine foods, so the bloodworms are an occasional treat). Larger fishes also receive frozen krill, frozen formula foods, fresh scallops, and pieces of salmon. I also use live blackworms and earthworms (usually chopped) to entice picky eaters to feed, but I try to wean the fish onto the more nutritious marine foods.
Sinking shrimp pellets, algae wafers, and Vibragro granules provide food for crabs, snails, and some fish. Nori sheets are also occasionally provided to the fish.
To provide shelter for the fishes, I use clay flowerpots, slate, lava rock (which should house bacteria similarly to tropical liverock) and small rocks that I find in tidepools. I try to stack and arrange these so as to provide caves and overhangs for the fish and crabs.
You wont be able to buy native fish at your local store. You can collect your own. For some people, thats half the fun.
Collecting gear can be as simple or complex as you like, but it will affect where you can collect. (Most of this gear is available at local discount/mart stores such as Walmart or Bennys or a good Bait and Tackle shop)
Basic gear can be an aquarium dip net, a clean 5-gallon pail, and a pair of old sneakers. With this gear, you can wade sandy and rocky beaches, sweeping the net thru clumps of seaweed and seagrasses. A basic upgrade to this gear would include a long handle dip net (with fine mesh), a pair of "aqua-sox" beach shoes, and a small battery powered air pump with airline and airstone.
Another option is passive collecting gear minnow traps and umbrella nets. Both are baited and lowered to the bottom, usually off of a pier or jetty. The umbrella net looks like an up-side down umbrella, with 1/14 mesh replacing the usual umbrellas nylon. I like to use these methods on days when collecting fishes isnt my first priority usually when Im fishing for striped bass or bluefish. I set the trap or net, fish for a while, then go back and see what Ive caught.
The most effective collecting method Ive found also takes the most effort seining. A seine is a long net, usually 4-6 ft tall and 10-20 ft long, with tall poles at each end. Although a single person can use a seine, I find I have the best success with two or three people. Two people hold the poles, with the net stretched out between them, and wade thru the water about 3-4 feet deep. The third person can be used to chase fishes into the net. Seines work best over sandy beaches or flats with few large rocks. After a short drag over the bottom, the poles are turned horizontal and the net is lifted from the water, revealing the contents. If the net is much more than 10 ft long, it helps to roll up the ends of the net around the poles before lifting the net from the water, therefore herding the fishes into a smaller area.
It is important to use extreme care when wading or seining ledges and drop-offs are not always apparent before you get to them. I prefer to stick to beaches that I know well, and always bring a partner if I am exploring a new beach.
One last method that requires no equipment should be mentioned picking up old bottles and cans in the water many interesting fish, especially Opsanus tau, the Oyster Toadfish, enjoy making their homes in discarded bottles and cans. You may be surprised what you find in an old beer bottle.
Here is a list of fish that I caught around the shores of Massachusetts
Tautogolabrus adspersus - A member of the wrasse family, its common names include Cunner and Choggie. These active fish are colored differently depending on where they are found bright green if caught in seaweed, orange-red in rocky areas and around pilings. These are probably the easiest fish to collect I find them almost everywhere and using every method. I have seen these fish swimming along the seawall. They reach about 15 in the wild, but are rarely seen above 6. They are opportunistic carnivores (accept frozen foods well) and usually occur in schools.
Centropristis striata - The Black Seabass often shows up in my traps and occasionally in seines. It really gets too big for the home aquarium, but more importantly, it is classified as a gamefish and therefore there is a minimum size limit on these fish. The specific size limit depends upon the state you are in, but it is generally too large for aquaria of less than 150 gallons .
Fundulus heteroclitus and Fundulus majalis - The Mummichog and the Striped Killifish are two of the more common killies in Eastern waters. They can easily be collected in most estuaries and salt marshes. Along with a few other killie species, they dominate most of my seine hauls. I have found them to make great "dither" fish for the native marine aquarium, and I recently discovered that four of these fish can quickly clean up a 55 gallon tank that is overrun with filamentous algae. They readily accept frozen foods, and can be weaned onto a good quality flake food. On a good diet rich with color enhancing foods, they show excellent colors (especially F. heteroclitus, the mummichog). These very hardy fish make great candidates for a first native marine aquarium. If you have a freshwater or brackish tank, these fish are tough as nails. They can adapt to fresh, brackish, and saltwater. This is mainly because they are estuarine and have to be able to adapt to the quick rush of water when the tides change.
Syngnathus fuscus - The Northern Pipefish is a common resident of seagrass beds and salt marshes. It turns up frequently in seine hauls. Unfortunately, it can be a very hard fish to feed. Initially, small live foods (copepods, amphipods, brine shrimp nauplii, and adult brine shrimp) are required in copious quantities. Eventually the pipefish can be weaned onto some frozen foods, although it may be difficult to provide a proper diet. Because this fish shares its feeding method with the related seahorses, developments in seahorse care (including high quality frozen mysid shrimp and the use of refugiums) may make it easier to care for. It should be kept in a tank without any fishes that will compete with it for food.
Assorted flatfishes - There are many species of flatfish or flounders that can be found locally at a reasonable size for aquarium keeping (between 1 and 4 inches). The biggest problem, however, is determining what species you have. Many of the common species, including Fluke (Paralichthys dentatus) and Winter Flounder (Pseudopleuronectes americanus), are considered gamefish and can only be collected at a minimum size too large for most aquaria. If you do find a small flatfish that can be legally kept, they should be kept in an aquarium with a sandy bottom and non-aggressive tankmates. I usually start them feeding on blackworms, white worms, or grindal worms, then wean them onto frozen foods.
Crustaceans - Some of the crabs that are collected in seines, traps, and nets while collecting fishes are good candidates for the home aquarium. Small hermit crabs can make a nice clean-up crew. Swimming crabs such as Callinectes sapidus (Blue Crab) or Carcinides maenas (Green Crab) will get large in a surprisingly short amount of time, and turn into fish-eating machines! With hermit crabs it is important to provide extra snail shells in multiple sizes for the crabs to use as they grow.
Grass or glass shrimp (Palaemonetes pugio) are easy to catch. They can be quickly seined over mudflats and grassbeds, or dipnetted while wading (they seem to be attracted to bare feet). They are easy to care for, as long as the tank does not contain predatory fishes these shrimp are a natural prey item for many fishes. Also, make sure the tank is well covered, as these shrimp tend to jump when startled.
Do not keep any horseshoe crabs that you find. They are near-threatened and because of the way they reproduce, horseshoe crabs are on the decline. It may be illegal in some states to keep horseshoe crabs.
)