Blue Zebra Hillstream Loach (Gastromyzon sp. “Blue Zebra”):

Species Profile:

• High Velocity: The water moves with significant force, saturating it with oxygen.
• Sunlight: Clear shallow water allows sunlight to penetrate, encouraging the growth of biofilm and algae on submerged rocks.
• Structure: The riverbeds consist almost entirely of smooth boulders, cobblestones, and gravel, with very little submerged vegetation.

• Size: They are a compact species, typically reaching 4.0–5.5 cm (approx. 2 inches) in captivity.
• Colouration: The body is dark, usually slate-grey or black, adorned with pale, silvery-blue stripes or bands. The defining feature is the vibrant blue hue often visible on the dorsal and caudal fins, particularly when the fish is healthy and well-settled.
• Morphology: Their body is dorso-ventrally flattened (streamlined) to minimise water resistance.

• Minimum Size: A tank of 75–90 litres (approx. 60–80 cm length) is the minimum for a small group.
• Dimensions: A shallow, wide tank is preferable to a tall, narrow one to maximise the surface area for oxygen exchange.

• Turnover: Aim for a turnover rate of 15–20 times the tank volume per hour.
• Equipment: Usage of oversized external filters, internal powerheads, or a river-tank manifold system is highly recommended to create a unidirectional flow.
• Aeration: If the temperature rises, additional air stones or venturi valves must be used immediately, as warmer water holds less dissolved oxygen.

• Substrate: Fine sand or rounded gravel.
• Grazing Stones: The tank should be piled with smooth, water-worn river stones. It is beneficial to keep a rotation of stones in a separate container of water in direct sunlight to grow green algae, which can then be swapped into the tank as a natural food source.
• Lighting: Bright lighting is encouraged to promote the growth of “Aufwuchs” (the matrix of algae and microorganisms) on the rocks.

• Primary Diet: They feed on the biofilm (slime coat) and micro-invertebrates that live on algae-covered rocks. They do not typically eat long, hair algae.
• Supplements: Their diet must be supplemented with high-quality sinking foods.
  • Gel Foods: Repashy “Soilent Green” or similar gel mixes painted onto rocks are excellent.
  • Vegetables: Blanched courgette, kale, or spinach.
  • Frozen: Cyclops, daphnia, and bloodworms (fed sparingly) provide essential protein.

• Shoaling: They are social and should be kept in groups of 3 to 5 or more.
• “Topping” Displays: You may observe individuals “topping” one another—where one fish tries to cover the other. This is a dominance display, usually over a prime grazing rock, and is rarely harmful.
• Tank Mates: Keep them with other cool-water, rheophilic (current-loving) species:
  • White Cloud Mountain Minnows (Tanichthys albonubes)
  • Zebra Danios (Danio rerio)
  • Other Hillstream Loaches (e.g., Sewellia lineolata)
  • Stiphodon Gobies

• Spawning: They are believed to dig small pits in the substrate under the cover of rocks to deposit eggs.
• Triggers: A cool water change followed by a period of heavy feeding may trigger spawning activity.

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