# First Observation of Embryonic Development and Paralarvae of Amphioctopus kagoshimensis

## TL;DR

This study provides the first detailed observation of the embryonic development and early life stages of the octopus species Amphioctopus kagoshimensis under controlled conditions.

## Contribution

The first comprehensive documentation of A. kagoshimensis embryonic development and paralarval stages under controlled aquaculture conditions.

## Key findings

- Embryonic development of A. kagoshimensis lasts 29–30 days at 22.0–24.5 °C with 20 distinguishable stages.
- Paralarvae exhibit planktonic behavior, phototaxis, and chromatophore development, surviving up to 30 days under lab conditions.
- The species shows potential as a model for developmental studies and aquaculture due to its manageable size and breeding traits.

## Abstract

Understanding the early development of cephalopods is essential for advancing aquaculture. Amphioctopus kagoshimensis, a merobenthic octopus species, has attracted increasing interest for artificial breeding. However, its reproductive and developmental characteristics remain poorly known. In this study, we successfully induced spawning and observed the complete embryonic development of A. kagoshimensis under controlled conditions at 22.0–24.5 °C and salinity of 29–32‰. Each female laid approximately 4000–5000 eggs (2.60 ± 0.05 mm in length). The embryos hatched after 29–30 days, passing through 20 distinguishable developmental stages. Newly hatched paralarvae were planktonic, with a mantle length of 1.58 ± 0.03 mm, and displayed phototactic behavior and ink expulsion. Despite high mortality, a small portion of paralarvae survived over 30 days under current rearing conditions. These results provide the first developmental baseline for this species and will facilitate future efforts in larval rearing, broodstock development, and potential aquaculture of A. kagoshimensis.

To evaluate the aquaculture potential of Amphioctopus kagoshimensis, we investigated the reproductive biology, embryonic development, and early paralarval morphology of Amphioctopus kagoshimensis under controlled laboratory conditions. Each adult specimen collected from the coastal waters of Fujian Province spawned approximately 4000–5000 eggs (mean ± SD: 4375 ± 478 eggs), with an overall hatching rate of 75% ± 10% (n = 2). Embryonic development lasted approximately 30 days at 22.0–24.5 °C and followed a classical 20-stage pattern. Hatchlings measured an average mantle length of 1.4 ± 0.1 mm and exhibited a merobenthic strategy, characterized by planktonic paralarvae with progressive morphological differentiation. The chromatophores appeared progressively on the head, mantle, arms, and funnel, with numbers increasing from 5 to 23 per arm by 30 days post-hatching. Paralarvae demonstrated active swimming, feeding behavior, and arm sucker development during rearing. By day 30, mantle length reached 2.5 mm, with significant growth in arm length and behavioral complexity. Its relatively small adult size (mantle length 8 cm), a moderate egg size (2.6 mm), fecundity and successful artificial incubation and 30-day paralarvae seedling suggested it may be a suitable model species for developmental studies and potential candidate for merobenthic octopod aquaculture in East Asia.