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Lined seahorse

Hippocampus erectus

Also known as Horsefish

Fishes › Seahorses and pipefish (Syngnathiformes) › Syngnathidae (Seahorses and pipefish)

The lined seahorse (Hippocampus erectus), northern seahorse or spotted seahorse, is a species of fish that belongs to the family Syngnathidae.

Aquarium hobby

Experience: Advanced

Lined seahorse — Photo: MattSullivan from Boston, MA, USA, CC BY 2.0, via Wikimedia Commons

Photo: MattSullivan from Boston, MA, USA, CC BY 2.0, via Wikimedia Commons

FamilySeahorses and pipefish

Record lifespan4.7 years

Adult lengthup to 7.5 in

WaterSaltwater

Care at a glance

Species-specific values

Values researched for this exact species. Where they differ from the group guide below, follow these. Air, surface and water temperatures are listed separately, and each source is kept as published rather than averaged.

Water temperature	74–78 °F Care table; tropical species. Historical source; retained separately from breeder recommendations.	287
Preferred water temperature	75–78 °F Breeder recommendation; distinguish optimum from broader tolerance.	288
Water temperature tolerance	68–82 °F Breeder’s stated acceptable limits; not a preferred operating range.	288
Water pH	8.2–8.4 pH	288
Water specific gravity	1.022–1.025 Source measurement reference temperature unspecified; not salinity in ppt.	288

Species-specific aquarium care

Tank: At least 30 in long and 15 in front to back for one adult (adults commonly reach about 7.5 in / 19 cm).
Water: Marine.
Temperature: 50–81°F (range recorded for this species).
Layout: Lives around reefs and rockwork: give caves, overhangs and swimming room along the rock.
Diet: FishBase classes it as a carnivore.

Calculated from this species' own FishBase record: tank size from its typical adult length and swimming zone, water values from its recorded ranges. The group guide below fills in general care.

Care guide

Group care guide

Seahorses and pipefish

Applies to most species in this group. Habitat: Seagrass beds and reefs. Individual species can differ, so compare with the species numbers above and the linked sources.

Housing & setup

Calm, tall tanks with hitching posts, cooler temperatures for many species, and peaceful tankmates.

Sources 117 119 164 118 287 288

Climate & lighting

Starting point only: Separates temperate, subtropical and tropical seahorses and preserves source disagreement. Check the species-specific values for this animal where shown.

Water

72–77°F

Sources 117 119 164 118 287 288

Diet

Verify the species and demonstrated food intake. Many larger captive-bred seahorses eat suitable frozen foods; Hippocampus zosterae requires small live enriched Artemia nauplii in the cited care guide.

Sources 117 119 164 118 287 288

Health watch

Bacterial infections and starvation; buy captive-bred. All seahorses are CITES Appendix II.

Sources 117 119 164 118 287 288

Understanding the animal

About this animal

H. erectus is a diurnal species with an approximate length of 15 cm (5.9 inches) and lifespan of one to four years. The H. erectus species can be found in myriad colors, from greys and blacks to reds, greens, and oranges.

Quoted from the Wikipedia article “Lined seahorse” (CC BY-SA 4.0) 174

In the wild

From this species’ own FishBase record (habitat, bottom type, water and breeding data), not its family. Good care copies these conditions.¹

Where it lives	Lives in the sea, in seagrass beds, open ocean. Lives around reefs. Generally in coastal waters; often around man-made structures.
Ground it lives on	Over sand, gravel, rock, rubble, aquatic plants.
Water it lives in	Marine, 50–81 °F (10–27 °C), depth 0–100 m.
Climate	Subtropical climate.
Behavior to plan for	Breeding: external brooders, paternal parental care.

What this means for care

Keep water within its wild range, 50–81 °F.
Use a soft, fine bottom; it lives over fine sediment in the wild.
Provide rockwork with crevices to hide in.
Add plants, roots, wood or leaf litter like its wild habitat.
Parents guard eggs or young, so expect territorial behavior when breeding.

FishBase species summary: Hippocampus erectus

From the sources

Quoted from the matching sections of reputable sources for this exact species. Specialist databases are used first; Wikipedia (community-edited, CC BY-SA 4.0) only fills gaps. Other sources are short credited quotes.

Overview	The lined seahorse (Hippocampus erectus), northern seahorse or spotted seahorse, is a species of fish that belongs to the family Syngnathidae. H. erectus is a diurnal species with an approximate length of 15 cm and lifespan of one to four years. The H. erectus species can be found in myriad colors, from greys and blacks to reds, greens, and oranges. The lined seahorse lives in the western Atlantic Ocean as far north as Cape Cod and as far south as the Caribbean, Mexico, and Venezuela. — Wikipedia (community-edited)
Where it lives	Home ranges Population dynamics Growth parameters Max. ages / sizes Length-weight rel. Length-frequencies Mass conversion Recruitment Abundance Life cycle Reproduction Maturity Maturity/Gills rel. — FishBase
Wild diet	The seahorse, like all of the species of the family Syngnathidae, require living food. — Animal Diversity Web
Behavior	Hippocampus erectus swims weakly, propelled largely by the rapid motion of its dorsal fin and pectoral fins. — Animal Diversity Web
Reproduction	Incubates eggs in an external marsupium. Gestation period 20-21 days but varies with water temperature. — FishBase
Appearance and size	Maximum length 17.8 cm sl male/unsexed; maximum reported age 1.00 years. — FishBase
Biology	Generally in coastal waters; often around man-made structures. Usually attached to gorgonians or seagrasses but may occur in floating Sargassum or swimming freely in midwater. Those that live in Sargassum usually have bony protuberances and fleshy tabs that may serve as camouflage. — FishBase
Conservation	Seahorse populations in the wild could vanish if they continue to be exploited for traditional Chinese medicines, the aquarium trade, and as tourist curios. — Animal Diversity Web

Data and studies

Researched care notes

Findings checked against veterinary, zoo, welfare, keeper and peer-reviewed sources. Air, basking-surface and water temperatures are kept separate, and where sources disagree both are shown. “Study” notes report what a paper measured, not a universal rule.

Seahorses (Hippocampus erectus)

Water / disagreement: Ocean Rider calls 75–78°F (23.9–25.6°C) optimal for its H. erectus line, while Seahorse Savvy recommends 70–74°F (21.1–23.3°C); preserve breeder provenance rather than publishing their arithmetic midpoint.¹^,²
Ocean Rider specifies seawater specific gravity 1.022–1.025 for its H. erectus; specific gravity is dimensionless and should not be stored as ppm salinity.¹
Confirm whether an acquired captive-bred seahorse already accepts frozen food; Ocean Rider explicitly pretrains its animals to eat frozen mysis.³

Seahorses (group; historical propagation evidence)

Researched for this genus; applies to its species unless a species note says otherwise.

The report found value in mysid prey and noted that Artemia requires enrichment to improve nutritional usefulness. Reported institutional practice; confidence LOW.⁴
Separate species breeding tanks provided vertical courtship space. Obtain current species-specific guidance before adapting this system. Confidence: LOW.⁴

The numbers

Each bar is what one source reports. Where several sources weigh in, the dashed gold band marks their average.

Maximum recorded lifespan

Highest reported4.7years

AnAge 1624.7

FishBase 1644.7

Longest recorded lifespan reported by each database; typical lifespans are usually shorter. The AnAge record comes from an animal in human care.

Adult length

Reported7.5in

FishBase 1647.5

Maximum recorded length. Fish in home aquariums often stay smaller than wild records.

Water temperature

Reported50–81°F

FishBase 16450–81

Range the species tolerates in nature; aim for the middle.

Female maturity

Reported9months

AnAge 1629

Veterinary & husbandry research

Draft genome of the lined seahorse, Hippocampus erectus Lin Q et al., GigaScience 2017
Retrospective study of phaeohyphomycosis in aquarium-housed fish, with first descriptions of Exophiala lecanii-corni and Neodevriesia cladophorae in fish Armwood AR et al., Journal of fish diseases 2021
Mixed metazoan and bacterial infection of the gas bladder of the lined seahorse-a case report Anderson PA et al., Journal of aquatic animal health 2013
Isolation, identification, and histopathological analysis of Vibrio tubiashii from lined seahorse Hippocampus erectus Shao P et al., Diseases of aquatic organisms 2019

Peer-reviewed papers that mention this species alongside captivity, zoos, veterinary care or aquaculture. Some cover several species or mention it only in passing, so check the abstract. See all 18 on PubMed → 170

Federal legal snapshot

Some federal rules apply

CITES Appendix endix II. Appendix III: international trade from the listing country needs CITES paperwork. No effect on buying captive-bred animals within the U.S. 173 186

State law decides most of it. Each state sets its own permits and bans for exotic, native, venomous and dangerous animals, and cities and counties can be stricter. Find your state agency →

Not covered by the Animal Welfare Act

The Act only covers warm-blooded animals. Reptiles, amphibians, fish and invertebrates have no federal care standards, even at licensed facilities; state and local rules may still apply.

Kept in captivity?

Every species on this site needs evidence that people actually keep it. For this one:

AnAge has a longevity record from an animal in captivity
FishBase records it in the aquarium trade (Aquarium=commercial; AquariumFishII=based mainly on capture; captive longevity record)
243 iNaturalist observations of captive animals

Sources for this sheet

AnAge: The Animal Ageing and Longevity Database (Human Ageing Genomic Resources) Peer-reviewed researchCurated, referenced longevity and life-history records for thousands of species; maximum lifespans are often from zoo animals.
FishBase (Froese & Pauly, eds.), version 24.07 Peer-reviewed researchThe global scientific database on fishes, maintained by a consortium of research institutions; every value is referenced.
Species+ (UNEP-WCMC and the CITES Secretariat) Zoo, university or veterinaryThe official database of species listed under CITES.
USFWS International Affairs: CITES Zoo, university or veterinaryFederal agency that issues CITES permits.
Merck Veterinary Manual: Management of aquarium fish Zoo, university or veterinaryThe Merck Veterinary Manual: a standard veterinary reference written and reviewed by veterinary specialists.
Merck Veterinary Manual: Types and features of aquatic systems Zoo, university or veterinaryThe Merck Veterinary Manual: a standard veterinary reference written and reviewed by veterinary specialists.
Merck Veterinary Manual: Nutritional diseases of fish Zoo, university or veterinaryThe Merck Veterinary Manual: a standard veterinary reference written and reviewed by veterinary specialists.
Seahorse.org: Seahorse facts and care information (historical keeper guide) Experienced keeper or breederAdded in the 2026 source-checked care-guide review.
Ocean Rider: Sunburst Hippocampus erectus care sheet Experienced keeper or breederAdded in the 2026 source-checked care-guide review.
Wikipedia (species article) Community referenceFree encyclopedia; useful overviews with their own citations. Intro text is quoted under CC BY-SA 4.0.
PubMed (U.S. National Library of Medicine) Peer-reviewed researchIndex of peer-reviewed veterinary, zoo and husbandry research.
iNaturalist (captive observations) Community referenceCommunity observation platform run by the California Academy of Sciences and National Geographic; observations marked captive show animals living in homes, zoos and aquariums.