Symptoms to Look For
Check if your shrimp are showing any of these symptoms. Symptoms are grouped by severity to help you assess the situation.
Early Warning
-
Small shrimp-like creatures swimming on their sides
Visual: Curved bodies (5-15mm) that swim sideways or erratically
-
Quick, jerky swimming motion different from shrimp
Visual: Rapid darting movements, often sideways
Moderate
-
Gathering at food sources aggressively
Visual: Scuds competing with shrimp for food
-
Population rapidly increasing
Visual: Numbers growing from few to many within weeks
-
Scuds around molting or weak shrimp
Visual: Multiple scuds investigating vulnerable shrimp
Severe
-
Scuds noticeably outnumbering shrimp
Visual: More scuds visible than shrimp
Does this match what you see? If your shrimp are showing multiple severe symptoms, act immediately. Early symptoms give you more time to correct the issue.
Possible Causes
Causes are listed by likelihood. Start with the most common causes and work your way down.
Hitchhiked on Plants
By far the most common introduction method. Scuds and their eggs hide among plant roots and leaves, surviving quarantine if not specifically checked.
Did you add new plants recently? Scuds usually appear 1-3 weeks after plant additions.
Introduced with Live Foods
Live food cultures, especially from outdoor sources or shared between hobbyists, may contain scuds or scud eggs.
Do you feed live foods? Cultures from ponds or shared sources may contain scuds.
Came with Other Livestock
Scuds can be in bags with purchased fish or shrimp, hiding in plants included with livestock.
Did scuds appear after adding any new livestock? They may have been in the transport water or plants.
Already Present at Low Numbers
Small scud populations can exist unnoticed until overfeeding or tank conditions trigger population growth.
Scuds may have been present for months. Increased feeding or organic matter triggered visible numbers.
Solutions
Option 1: Assessment: Decide If Action Is Needed
- 1
Understand scud behavior
Scuds are detritivores like shrimp - they eat decaying matter, biofilm, and algae. They don't hunt or attack healthy shrimp. Many keepers accept them as harmless cleanup crew.
- 2
Assess population level
A few scuds are not a problem. Concern arises when populations explode and compete significantly for food resources.
- 3
Observe interactions
Watch how scuds behave around shrimp. If they're just coexisting, intervention may not be needed. If they're aggressively competing for food or bothering molting shrimp, consider action.
- 4
Decide on approach
Options range from acceptance (they're harmless) to reduction (trapping, reduced feeding) to elimination (chemical or predator methods).
Option 2: Population Control (Non-Chemical)
- 1
Reduce feeding
Less food means less scud population growth. Feed only what shrimp consume in 1-2 hours. Scud populations decline without abundant food.
- 2
Use traps
Scud traps (similar to planaria traps) baited with meat or fish food can catch significant numbers. Check traps daily and dispose of contents.
- 3
Manual removal during feeding
Scuds swarm food. When they gather on food, remove the food (and scuds) with a net. Repeat at each feeding.
- 4
Add fish predators
Many fish eat scuds readily - bettas, small cichlids, gouramis, even many community fish. However, these fish may also eat shrimplets or stress shrimp.
Fish that eat scuds often also eat or stress shrimp
- 5
Maintain efforts long-term
Scuds reproduce quickly. Population control requires ongoing effort. You may reduce but not eliminate them without chemical treatment.
Recommended Products
These are informational recommendations only. Not affiliated with any brands.
Option 3: Chemical Elimination
This kills snails and may not be necessary if scuds aren't causing problems
- 1
Remove all snails
Fenbendazole (No-Planaria) kills snails. Remove all snails to a separate container before treatment.
All snails will die if left in treated tank
- 2
Apply fenbendazole treatment
Use No-Planaria or Panacur C at standard dose (0.1g per 10 gallons). Scuds are killed by the same treatment that kills planaria and hydra.
- 3
Wait 48-72 hours
Scuds will die within this timeframe. You'll see dead scuds on the substrate.
- 4
Water change and cleanup
Remove dead scuds with gravel vacuum. Do 25-30% water change. Dead scuds decompose and release ammonia.
- 5
Second treatment if needed
If any scuds survive, repeat treatment after one week.
- 6
Run carbon and return snails
After 1 week post-treatment, run activated carbon 24-48 hours. Then snails can safely return.
Recommended Products
These are informational recommendations only. Not affiliated with any brands.
Prevention Tips
Follow these practices to help prevent this problem from occurring in the future.
- Quarantine new plants for 2-4 weeks - scuds become visible during this time
- Inspect plants carefully before adding - look for movement in root masses
- Rinse plants thoroughly under running water
- Consider bleach or alum dip for new plants (kills scuds but may harm sensitive plants)
- Avoid live foods from unknown sources
- Don't overfeed - excess food enables scud population growth
- Accept that some scuds may not be worth eliminating if populations stay low
Track These Parameters with ShrimpKeeper
Get alerts when your parameters drift out of range, see historical trends, and catch problems before they become emergencies.
Download FreeScuds (also called amphipods, gammarus, or side-swimmers) are small crustaceans related to shrimp. They're extremely common hitchhikers on aquarium plants and cause much debate among shrimp keepers about whether they're problematic. Identification: - Size: 5-15mm (smaller than most adult shrimp) - Shape: Curved, laterally compressed (flattened side to side) - Movement: Characteristic sideways swimming, quick darting motions - Color: Usually gray, tan, or greenish - Distinguish from: Shrimp (shrimp swim forward, have longer rostrum), seed shrimp/ostracods (much smaller, round) The scud debate: Opinions vary widely on whether scuds are problematic: **"They're harmless" perspective:** - Scuds are detritivores, eating the same things shrimp eat - They don't hunt or attack healthy shrimp - They provide food for fish - Many tanks have coexisting scud and shrimp populations **"They're problematic" perspective:** - Scuds compete aggressively for food - They may outcompete shrimplets for resources - Reports of scuds bothering/eating molting shrimp (disputed) - Large populations are unsightly - They reproduce very quickly and can overwhelm tanks The truth is probably situational. In well-fed tanks with healthy shrimp colonies, scuds may coexist fine. In tanks where resources are limited, competition may impact shrimplet survival. Reports of scuds attacking molting shrimp are controversial - they may be scavenging already-dead shrimp. Population dynamics: Scuds reproduce rapidly in favorable conditions. Females carry eggs in a brood pouch and can produce new generations every few weeks. Populations can explode from a few individuals to hundreds within a month if food is abundant. Reducing feeding is the most effective non-chemical control. Treatment considerations: Before treating, honestly assess whether scuds are actually causing problems. If shrimp are breeding successfully and the tank is healthy, scuds may be more aesthetic annoyance than real threat. Chemical treatment (fenbendazole) is effective but kills snails and may be unnecessary intervention. If you do want scuds gone, fenbendazole (No-Planaria) reliably kills them at doses safe for shrimp. This is the same treatment used for planaria and hydra.
Frequently Asked Questions
Scuds don't actively hunt or attack healthy adult shrimp. The main concerns are: competition for food (especially affecting shrimplets), possible harassment of molting shrimp (disputed), and large populations overwhelming tanks. Many tanks have coexisting scud and shrimp populations without problems.
Almost always from plants. Scuds and their eggs hide in plant roots and leaves, surviving even thorough rinsing. They can also arrive with live foods, in transport water with new livestock, or on shared equipment. They often appear 1-3 weeks after adding new plants.
It depends on your situation. If shrimp are breeding successfully and scud numbers are stable, coexistence may be fine. If scud populations are exploding, competing aggressively for food, or you find them unsightly, control or elimination may be worthwhile. There's no universal right answer.
Many fish eat scuds readily - bettas, gouramis, cichlids, larger tetras, most predatory fish. However, fish that eat scuds often also eat or stress shrimp. Adding fish predators trades one potential problem for another in shrimp breeding tanks.
Scuds swim sideways in quick, jerky motions and have a curved, laterally compressed body. Baby shrimp look like tiny versions of adults - they swim forward, have the typical shrimp shape with visible rostrum (nose), and move more gracefully. Scuds also typically hide more during the day.
Yes, fenbendazole (No-Planaria, Panacur C) kills scuds effectively at the same dose used for planaria and hydra. However, it also kills all snails. If you're treating for scuds alone, consider whether chemical treatment is necessary or if population control methods are sufficient.
This is debated. Scuds are primarily detritivores (eat dead/decaying matter) but are opportunistic. Some keepers report scuds attacking very small shrimplets; others keep both populations together without issues. The bigger concern may be competition for food rather than direct predation.
Track Your Parameters with ShrimpKeeper
Most shrimp problems stem from parameter issues. Track your water quality, get alerts when things drift, and prevent problems before they happen.