Req 7d — Freshwater Aquarium

Most aquariums are displays — you observe what happens. A native freshwater aquarium is an experiment. You’re creating a miniature ecosystem, stocking it with organisms that interact as they would in a real pond or stream, and watching 60 days of ecological relationships unfold in a glass box. Every food chain, every competition for territory, every life cycle you witness is the same dynamic that a fisheries manager sees at lake scale. The difference is that you can watch it from 12 inches away.

Planning Your Aquarium

Tank Size and Setup

A 10–20 gallon aquarium works well for this project. Larger is generally more stable — it gives each species more space and makes the chemistry easier to manage. You’ll need:

• Substrate: Aquarium gravel, sand, or ideally a mix of both. Native pond sediment can also work but introduces unknowns.
• Filtration: A basic aquarium filter (hang-on-back or sponge filter) keeps water oxygenated and filtered. If you’re collecting organisms from a clean water source, a sponge filter is gentler on invertebrates.
• Lighting: Natural light (but not direct sunlight, which causes temperature swings and algae blooms) or a simple aquarium light on a timer
• Hiding spots: Smooth rocks, driftwood, and dense plant groupings give animals cover — which reduces stress and shows you more natural behavior

Do not use tap water without dechlorinating it first — chlorine kills invertebrates. Fill the tank a few days before adding organisms, or use a dechlorinator available at any aquarium store.

Collecting Native Organisms

Check your state’s regulations before collecting anything. Most states allow limited collection of common invertebrates and small fish for educational purposes, but some require a permit, and some species are protected. A note from a teacher or merit badge counselor explaining the educational purpose can help if you’re questioned.

Where to collect:

• A clean, unpolluted stream or pond in your area
• The edge of a natural lake (wade carefully in shallow areas)
• Vernal pools in spring for tadpoles and salamander larvae
• Submerged plant beds for invertebrates

How to collect:

• D-frame aquatic net (mesh net on a D-shaped frame) for sweeping through aquatic plants
• White enamel pan or light-colored bucket — pour the net into it and pick through carefully
• Small flashlight for spotting invertebrates in stream drift at night
• Seining (dragging a fine-mesh net between two people through shallow water) for small fish

Selecting Your Species

Four or more native plant species (choose from what’s naturally present in local water bodies):

• Elodea (waterweed) — common, hardy, fast-growing, excellent oxygenator
• Duckweed — floating, provides shade and cover
• Water starwort — delicate, good for invertebrates to cling to
• Hornwort — excellent floating/submerged plant that requires no rooting
• Water milfoil (native species, not Eurasian milfoil) — dense structure
• Arrowhead — emergent plant, provides above-water stem structure

Four or more native animal species — the requirement examples are helpful guides:

• Whirligig beetles (Gyrinidae): Small oval beetles that spin circles on the water surface; predatory
• Freshwater shrimp (scuds/amphipods): Tiny crustaceans in leaf litter and among plants; important prey base
• Tadpoles: American toad, green frog, or bullfrog tadpoles are robust and easy to observe
• Water snails: Bladder snails, ramshorn snails, and pond snails graze algae and are fascinating to observe
• Golden shiners or creek chubs: Hardy small fish that are native to most of the eastern U.S.
• Freshwater mussels: Check legality first — many are protected
• Dragonfly/damselfly nymphs: Fascinating predators, but they will eat other small inhabitants
• Water striders: Surface-dwelling predators that walk on water tension
• Caddisfly larvae: Build protective cases from sand grains and plant material
• Crayfish: Active and interesting, but will eat fish if they’re large enough

60 Days of Observation

Your counselor wants you to observe for 60 days because ecosystems reveal their dynamics over time. The first week you’ll see establishment behavior — species finding their territories, adjusting to the tank. By week two or three, you’ll start seeing predator-prey interactions. By week six or eight, you may see life cycle events: snail egg masses on the glass, tadpoles developing legs, insects molting.

What to observe and record:

• Which species are most active? At what times of day?
• What is eating what? Can you see a food chain?
• Are any species thriving? Declining? Why?
• Life cycle events: egg masses, molts, metamorphosis, death
• Water quality: Is algae growing excessively? Is the water cloudy or clear?
• Species interactions: aggression, hiding behavior, schooling, territorial defense

Keep a brief journal — one observation entry per week minimum, more if something interesting is happening. Note the date and what you observed.

Discussing Life Cycles, Food Chains, and Management

When you meet with your counselor, be prepared to discuss three specific topics:

Life cycles: What did you actually observe? Tadpole-to-frog metamorphosis is the most dramatic if you have tadpoles. Snail reproduction (tiny egg clusters on glass) is easily missed. Insect molts (shedding the exoskeleton) leave transparent “ghost” skins behind. Even just observing the growth of plants over 60 days is a life cycle observation.

Food chains: Can you trace a food chain from your aquarium? Example: Algae → snails → dragonfly nymph. Who was eating whom? Was the predator’s population limited by prey availability?

Management needs: This is the key management connection. What did your aquarium reveal about how this ecosystem needs to be managed?

• Did one species overpopulate and need “harvest” to stay in balance?
• Did a predator eliminate prey and then starve?
• Did algae overgrow because there weren’t enough grazers?
• What would happen if you introduced an invasive species? These are the same questions a real lake manager faces at larger scale.

Disposal of Organisms

The requirement includes an important warning: check local laws before releasing organisms. Releasing organisms — even native species — from an aquarium into the wild is restricted or prohibited in most states. Reasons include:

• Disease transfer: Aquarium fish can carry diseases that wild populations haven’t been exposed to
• Genetic concerns: Mixing hatchery or captive-raised populations with wild populations can have genetic consequences
• Accidental introduction of plants: Aquatic plants spread easily and many become invasive

Acceptable disposal methods:

• Return organisms exactly to the water body where they were collected, same day if possible
• Find a new home with another Scout, educator, or aquarium enthusiast
• Contact a local pet store or nature center — many accept aquarium donations
• If organisms must be humanely euthanized, your counselor can advise on appropriate methods

Your 60-day observation project is done and your counselor discussion is complete. One requirement left: exploring where this science can take you as a career.