Hydra vulgaris — Culture Maintenance

Overview

Routine maintenance protocol for Hydra vulgaris laboratory cultures following a 9-day repeating cycle. Animals are fed freshly-hatched Artemia salina nauplii raised in the UFO Hobby hatchery using a brine solution of Hydra Medium and NaCl. Each feeding delivers 4–5 nauplii per individual. Water changes are performed every 2–3 days to control biofilm and slime build-up. Hydra Medium (HM) can be prepared using the HM Calculator ↗ or substituted with Volvic mineral water or, in Bulgaria, DEVIN pink-label water. All biological waste must be inactivated with H₂O₂ or 70% ethanol before disposal.

9-Day Cycle at a Glance

Day 1

Prepare brine & start Artemia hatch

Day 2

Wash nauplii & feed hydra

Day 3

Water change + feed remainder

Day 4

Water change or clean container

Day 5

Rest — no action

Day 6

Start new Artemia hatch

Day 7

Wash nauplii & feed hydra

Day 8

Water change + feed + clean hatchery

Day 9 → Day 1

Cycle restarts — new brine

Safety

⚠

Hazard Warning — Flammable & Irritant Disposal Reagents; Live Organism Containment

GHS02
FLAMMABLE

GHS07
IRRITANT

Never discard live Hydra or Artemia into the drain or waste bin. All biological material must be inactivated with H₂O₂ or 70% ethanol for ≥ 10 min before disposal.
70% ethanol is flammable — keep away from open flames and ignition sources during inactivation steps.
H₂O₂ (≥ 3%) is an oxidiser and skin/eye irritant — wear nitrile gloves and avoid contact with mucous membranes.
Brine solution contains ~30 g/L NaCl — do not allow it to contaminate Hydra culture vessels or HM stock. Even trace carryover can stress or kill animals.
Keep culture vessels covered and labelled to prevent contamination and evaporation. Do not store next to chemicals or strong light sources.

Reagents & Equipment

#	Reagent / Item	CAS	Amount	Final conc.	Hazard
01	Hydra Medium (HM) Alt.: Volvic mineral water; DEVIN pink-label (BG)	—	≥ 1 L	—	—
02	Sodium chloride (NaCl)	7647-14-5	30 g	30 g / L	—
03	Sodium bicarbonate (NaHCO₃)	144-55-8	small pinch	trace	—
04	Artemia salina cysts (brine shrimp eggs)	—	~80 mm³	—	—
05	H₂O₂ (3–30%) or 70% ethanol For biological waste inactivation only	7722-84-1 / 64-17-5	as needed	≥ 3% / 70%	GHS02 GHS07
E1	UFO Hobby Artemia hatchery	—	1 ×	—	—
E2	3D-printed measuring spoon (~80 mm³) For Artemia cyst dosing — use if available	—	1 ×	—	—
E3	Petri dishes (Hydra culture vessels)	—	3 ×	—	—
E4	Transfer pipette, wide-bore (Pasteur)	—	1 ×	—	—
E5	50 mL Falcon tube	—	1 ×	—	—
E6	Glass beaker, 500–1 000 mL	—	1 ×	—	—
E7	Graduated cylinder, 1 000 mL	—	1 ×	—	—

Protocol Steps — 9-Day Cycle

#	Action	Time
Day 1 Brine Preparation & Artemia Hatch Setup
1.1	Prepare 1 L of brine solution: dissolve 30 g NaCl and a small pinch of NaHCO₃ in Hydra Medium. Stir until fully dissolved. Use a graduated cylinder for accuracy. HM (or Volvic / DEVIN pink-label water) is the recommended base — do not use tap water or distilled water.	~5 min
1.2	Fill the UFO Hobby hatchery with 750–800 mL of the prepared brine solution. The UFO hatchery separates hatched nauplii from unhatched cysts and empty shells via an inner ring — overfilling submerges this ring and defeats the separation. Keep the fill level within 750–800 mL.	~2 min
1.3	CHECK Add ~80 mm³ of Artemia cysts to the brine. Use the 3D-printed measuring spoon if available. This dose is calibrated for 3 full Petri dishes of Hydra. Adjust proportionally if culture size differs significantly.	~2 min
1.4	CHECK Close the hatchery securely. Place in a bright location (window or lamp). Do not move the hatchery until Day 2. Moving the hatchery causes empty chorion shells (which float outside the central ring) to drift inward through the sieve. Shells fed to Hydra cannot be digested and foul the culture. Artemia hatch within 24–36 h at room temperature. Bright light accelerates hatching.	—
Day 2 First Feeding
2.1	Remove the central sieve from the UFO hatchery containing the hatched Artemia nauplii.	~2 min
2.2	WASH Wash the nauplii 3 × 2 min with fresh Hydra Medium. Gently immerse the sieve in HM for each rinse cycle. Removing residual brine is critical — even a small NaCl carryover will stress or kill Hydra. Each rinse must be a full 2 minutes. A fourth rinse is advisable for sensitive or small cultures.	3 × 2 min
2.3	FEED Using a wide-bore transfer pipette, feed each Hydra culture. Aim for 4–5 nauplii per individual. Hydra should contract and extend tentacles toward prey within minutes. Remove excess nauplii from the dish after ~1 h to avoid fouling the medium.	~10–20 min
Day 3 Water Change + Second Feeding
3.1	CHECK Inspect culture vessels for slime / biofilm accumulation. Decide: light slime → water change only; heavy slime → full animal transfer with container clean.	~1 min
3.2a	(Light slime) Gently agitate the medium with a pipette tip to detach dead Artemia and settled particles from the bottom. Then decant all liquid into a beaker or remove by pipette. Refill dish with fresh HM. Some Hydra will detach and end up in the beaker during decanting — this is acceptable. Once the dish is refilled, create a slight whirlpool in the beaker; detached Hydra collect in the centre and can be pipetted back.	~5 min
3.2b	(Heavy slime) Transfer all Hydra to a 50 mL Falcon tube with fresh HM. Cap and shake to detach slime — do not shake excessively. Wait 2–3 min for animals to settle. Pipette clean Hydra back into a freshly rinsed dish filled with HM. Do not vortex — Hydra are fragile under strong mechanical stress. Discard slime-containing tube contents into a waste beaker; inactivate before drain disposal.	~10–15 min
3.3	FEED Feed remaining live Artemia nauplii from the hatchery sieve if still available. Wash first (as step 2.2) if not already done today.	~10 min
Day 4 Water Change
4.1	CLEAN Perform a water change or full container clean as per steps 3.2a or 3.2b, depending on slime level. No feeding today.	~5–15 min
Day 5 Rest — No Action Required
5.1	No action required. Optionally observe culture health visually (posture, tentacle extension, budding activity).	—
Day 6 New Artemia Hatch Initiated
6.1	HATCH Add a new dose of ~80 mm³ Artemia cysts directly to the existing brine already in the hatchery. Do not replace the brine. The old brine is reused — no need to prepare a fresh solution. Rinse the sieve if needed, then close the hatchery and do not move it. Bright location as before.	~10 min
Day 7 Second Cycle Feeding
7.1	REPEAT 2.1–2.3 Feed as on Day 2: remove sieve, wash nauplii 3 × 2 min with HM, feed 4–5 nauplii per Hydra.	see Day 2
Day 8 Water Change + Feed Remainder + Hatchery Clean
8.1	REPEAT 3.1–3.3 Perform water change and second feeding as on Day 3. Repeat steps 3.1 → 3.3.	see Day 3
8.2	CLEAN Empty and thoroughly clean the UFO hatchery: discard brine directly down the sink, disassemble and rinse all parts with tap water, then once with distilled water. Allow to air-dry. Artemia and cysts do not survive in fresh water — no inactivation of brine waste is required before drain disposal. Regular hatchery cleaning prevents biofilm, fungal growth, and salt crust that progressively reduce hatch rates.	~10 min
Day 9 → Day 1 Cycle Restarts
9.1	CYCLE Return to Day 1: prepare fresh brine and start a new Artemia hatch. The 9-day cycle continues indefinitely.	—

Notes & Tips

Concentrating Hydra without loss. To collect animals before a transfer or water change: decant or pipette out all medium into a beaker. Make a gentle whirlpool in the remaining drop — Hydra collect in the vortex centre due to their low mass. Transfer animals to a 50 mL Falcon tube with fresh HM, cap, and invert gently 2–3 times to detach slime. Wait 2–3 min for settling. Pipette clean animals back into a freshly rinsed dish.

Why the nauplii wash matters. Brine contains ~30 g/L NaCl — far above what Hydra tolerate. Three × 2-minute rinses in HM are the minimum; a fourth rinse is advisable for sensitive or budding-active cultures. Never skip this step, even when cultures appear robust.

Hydra Medium alternatives. If freshly prepared HM is unavailable, Volvic mineral water (France/EU-wide) or DEVIN pink-label water (Bulgaria) are well-established substitutes with a compatible mineral composition. Avoid carbonated, softened, or distilled water. Prepare HM using the 3-DRAKON Lab HM Calculator ↗ — the standard recipe follows Little et al. with K₂CO₃ replaced by KCl.

Biological waste disposal. Never discard live Hydra or Artemia into drains or waste bins. Add H₂O₂ to a final concentration of ~3%, or add 70% ethanol in excess, and wait at least 10 min before drain disposal. This prevents ecological contamination and complies with biosafety guidelines for model organism containment.

Culture health indicators. Healthy Hydra are elongated with fully extended tentacles when unfed. Contracted, ball-shaped animals indicate stress — check light, temperature (optimum ~18–20 °C), water quality, and pH. Budding is normal and indicates good condition; increase water-change frequency if budding leads to overcrowding. Discard contaminated dishes after inactivation.