Core Identification:
Gray-brown base coloration with large irregular round blotches; dorsal fin displaying distinct red–white–black horizontal bands.

I. Species Overview

Pseudogastromyzon cheni is a small Hillstream Loach endemic to China.
It belongs to:

• Order: Cypriniformes

• Family: Homalopteridae

• Genus: Pseudogastromyzon

← Back to Loach (genus overview)

The species is restricted to the upper Hanjiang River basin. Due to its extremely narrow distribution and habitat fragmentation.

Morphology

• Adult size: 6–8 cm (rarely exceeding 10 cm)

• Body form: Strongly depressed anterior body, flattened ventral surface

• Caudal region: Slightly compressed

• Overall shape: Shovel-like, adapted for adhesion in fast current

Head Structure

• Head short and flattened

• Snout blunt and rounded

• Mouth inferior and arched

• Rostral fold divided into three lobes with small papillae

• Two pairs of short barbels for detecting algae and food on rock surfaces

Fins

• Pectoral fins: Wide, laterally spreading

• Pelvic fins: Separate (not forming a suction disc)

• Caudal fin: Shallowly emarginate for current stabilization

Ecological Significance

This species functions as a natural algae grazer and indicator of clean, well-oxygenated stream systems.
Captive specimens should originate from legal captive breeding sources. Wild collection is strongly discouraged.

II. Coloration and Pattern

1. Body Color

• Base color: Gray to gray-brown

• Abdomen: Pale gray to milky white, unmarked

• Contrast: Clear separation between dorsal and ventral coloration

Environmental substrate may slightly influence tone intensity.

2. Diagnostic Blotches

The dorsal and lateral surfaces are covered with:

• Large, irregular round blotches

• Dark brown to blackish-brown coloration

• Scattered distribution without fixed pattern

• Clear spacing between markings

• No fine speckling

These blotches are the primary identifying feature.

3. Dorsal Fin Pattern (Key Identifier)

The dorsal fin displays a stable three-band structure:

• Outer margin: Deep red

• Middle band: Pure white

• Basal band: Black

The clean red–white–black layering is highly distinctive and stable.

4. Other Fins

• Pectoral & pelvic fins: Match body coloration

• Anal fin: Pale gray with faint distal reddish tint

• Caudal fin: Grayish, sometimes with subtle red at tips

III. Distribution and Habitat

1. Geographic Distribution

Endemic to the upper Hanjiang River basin, primarily:

• Changting (Fujian)

• Shanghang (Fujian)

• Yongding (Fujian)

• Limited marginal presence near the Fujian–Guangdong border

Populations are fragmented and geographically isolated.

2. Habitat Characteristics

Flow Regime

• Fast-flowing mountain streams

• Shallow riffles

• Continuous current required

Substrate

• Smooth cobbles and pebbles

• Minimal silt or sand accumulation

• Algal biofilm present on rock surfaces

Oxygenation

• High dissolved oxygen

• Clear, unpolluted water

Natural Parameter Range

• pH: 6.5–7.5

• Temperature: 17–25°C

• Thermal stress: Prolonged exposure above 28°C increases mortality risk

IV. Aquarium Setup

The aquarium should replicate a clean, fast-flowing stream environment.

Tank Dimensions

• Minimum: 40 × 30 × 30 cm

• Recommended: 60 cm or longer for stable current patterns

Substrate

• 3–5 cm layer of smooth rounded pebbles

• Neutral gray or brown tones

Water Flow

• Moderate to strong laminar flow

• Wave pump or powerhead recommended

• Ensure uniform circulation

Filtration

• High-efficiency biological filtration

• Strong oxygenation

• Stable nitrogen cycle

Structure & Layout

• Smooth stones for grazing and shelter

• Open layout to maintain water circulation

• Avoid cluttered aquascaping

V. Feeding and Husbandry

Primary Diet: Algal biofilm grazer

Captive success depends on maintaining natural algae growth.

Encourage Natural Feeding

• Provide regular lighting

• Allow controlled growth of diatoms and filamentous algae

Supplemental Feeding (Only if Needed)

• Spirulina wafers

• Algae-based sinking tablets

• Small amounts of blanched spinach

Feeding Frequency

• 1–2 times per week

• Small portions consumed within 5 minutes

• Remove uneaten food promptly

Avoid

• High-protein diets

• Overfeeding

• Frequent artificial feeding

VI. Water Parameters in Captivity

Stable water conditions are critical.

Optimal Range

• Temperature: 20–25°C

• Maximum tolerance: Avoid prolonged exposure above 28°C

• Winter minimum: ≥15°C

• Daily fluctuation: ≤2°C

Chemical Stability

• pH: 6.5–7.5

• Ammonia: 0 ppm

• Nitrite: 0 ppm

• High dissolved oxygen required

Water Changes

• 30–40% weekly

• Use aged, dechlorinated water

• Match tank temperature

• Avoid large sudden changes

VII. Tankmates and Stocking

Tankmates

Suitable:

• Peaceful hillstream loaches

• Rheophilic gobies

• Small current-adapted mid-water species

Unsuitable:

• Aggressive or territorial benthic fish

• Large predatory species

Stocking Density

• 40 cm tank: 3–6 individuals

• 60 cm tank: 6–12 individuals

Lower densities reduce competition and improve oxygen availability.

VIII. Reproductive Behavior (Wild)

Spawning season: Late spring to early summer (May–June)
Water temperature: 18–22°C

Spawning Site

• Fast, shallow riffles

• Smooth cobbles or rock crevices

Reproduction Type

• External fertilization

• Adhesive eggs

• No parental care

Larvae feed on plankton and algal film after hatching.
Captive breeding remains uncommon.

IX. Health Management

Common risks:

• Fungal infections

• Enteritis

• Hypoxia

• Stress-related mortality

Prevention

• Maintain strong oxygenation

• Keep stocking density moderate

• Ensure stable temperature

• Prevent physical injury

Intervention

• Isolate affected individuals

• Improve water conditions

• Partial water changes

• Mild, targeted medication when necessary

Most health issues resolve with environmental correction.

X. Conservation and Ethical Considerations

Pseudogastromyzon cheni has a highly restricted natural range and is vulnerable to:

• Habitat degradation

• Water pollution

• Overcollection

Responsible aquarists should:

• Purchase only legally captive-bred specimens

• Avoid wild collection

• Never release captive fish into natural waters

• Maintain stable, low-stress environments