Captive-Breeding Protocol & Rewilding Survivorship for the Banggai Cardinalfish
A closed-cycle, genetically managed breeding protocol for the endangered Pterapogon kauderni, and the 90-day post-release survivorship of soft-released, host-conditioned juveniles against the standing wild benchmark.
Abstract
The Banggai cardinalfish (AE-SPX-0001) is endangered by a narrow endemic range and relentless aquarium-trade collection of wild stock. Because it is a paternal mouthbrooder that skips a planktonic larval stage and releases fully-formed juveniles, it is unusually tractable for closed-cycle breeding — if broodstock genetics and juvenile conditioning are managed properly. We established a 28-pair breeding nucleus selected for maximal retained heterozygosity, ran it through a standardized spawning and rearing protocol, and produced 612 juveniles across three cohorts. Juveniles were conditioned to natural microhabitat (sea-urchin and anemone hosts) before a soft release into a restored patch reef. At 90 days, 68% of released juveniles survived versus a wild-cohort benchmark of 61%, with host fidelity equal to wild fish. Closed-cycle supply removes the trade's justification for wild collection, and the rewilding data show captive-bred fish are field-competent.
Background & Question
Two questions had to be answered together. First, the husbandry one: can we breed this species at scale on a documented protocol while keeping the broodstock genetically healthy across generations? Inbreeding depression is the silent killer of conservation breeding programs. Second, the ecological one: do captive-bred, captive-conditioned juveniles actually survive in the wild at a rate comparable to wild fish? A breeding program that produces animals which die on release is theater. We pre-registered a survivorship non-inferiority margin: rewilded survival must be within 10 percentage points of the wild benchmark to count the protocol as field-ready.
Methods
- Broodstock: 28 founder pairs genotyped at 14 microsatellite loci; pairings assigned by mean-kinship minimization to maximize retained heterozygosity (AE-MET-026 · Broodstock Genetic Diversity, He).
- Spawning & rearing: paternal mouthbrooding to full juvenile release (~20–24 days); juveniles weaned onto enriched live Artemia then frozen diet; tank chemistry held per AE-SOP-0112 · Dynamic Water-Change Protocol and AE-SOP-0101 · Specimen Accession & Quarantine.
- Conditioning: pre-release exposure to live host structures (AE-SPX-0058 · Bubble-Tip Anemone, urchin spine canopy) to imprint shelter-seeking behaviour.
- Release: soft release via acclimation cages on a restored patch reef per AE-SOP-0410 · Rewilding Release Readiness; n=180 released, paired wild-benchmark cohort of 120 tracked in parallel.
- Monitoring: visual-implant elastomer marks; weekly diver census and ROV photostation; survival and host fidelity logged; spawn/survival referenced to AE-MET-023 · Hatchery Spawn Index, AE-MET-024 · Fry Survival, AE-MET-025 · Rewilding Releases.
- Statistics: Kaplan–Meier survival with log-rank; non-inferiority test against the wild benchmark.
Findings
The breeding nucleus performed: spawn index 88%, juvenile rearing survival to release 79%, and — critically — retained heterozygosity held at He 0.71 across the founding generation, with no measurable drop. In the field, rewilded juveniles reached 68% survival at 90 days, statistically non-inferior to (in fact slightly above) the 61% wild benchmark; host fidelity was indistinguishable from wild fish. The conditioning step mattered: an earlier unconditioned pilot batch (not counted here) had shown far weaker shelter-seeking. The protocol meets both the husbandry and the rewilding criteria and has been promoted to standard practice.
| Stage | Metric | Result | Target / benchmark |
|---|---|---|---|
| Spawning | Spawn index | 88% | ≥80% |
| Rearing | Survival to release | 79% | ≥70% |
| Genetics | Retained He | 0.71 | ≥0.70 |
| Rewilding | 90-day survival | 68% | wild 61% (non-inferior) |
Implications
This is conservation breeding doing exactly what it should: producing field-competent animals that remove the market rationale for stripping wild reefs. A documented, genetically-managed closed cycle means the League can flood the legitimate trade with captive-bred stock and starve the wild-collection operations the dispatch desk tracks. The 28-pair nucleus and its kinship matrix are archived in the Marine Genebank as a managed conservation line, and the rewilding survivorship data become the evidentiary basis for expanding releases to additional restored patch reefs. Husbandry, here, is a form of enforcement.
References & Linked Records
- AE-SPX-0001 — Banggai Cardinalfish (Pterapogon kauderni)
- AE-SPX-0058 — Bubble-Tip Anemone (release host)
- AE-MET-023 — Hatchery Spawn Index
- AE-MET-024 — Fry Survival
- AE-MET-026 — Broodstock Genetic Diversity
- AE-SOP-0410 — Rewilding Release Readiness
- AE-SOP-0101 — Specimen Accession & Quarantine
- Related log: RL-2090-018 — Heat-Tolerant Coral Genotype Selection