Acheilognathus signifer is an endemic Korean bittering designated as an endangered wild animals in Korea. We attempted to survey spawning ecology and analyze why spawning adaptation includes the use of mussels and discuss conservation between the bitterling and mussels. A survey was carried out in three populations where the bittering and mussel coexist as follows: 1) the Goesan population (Cheongcheon-myeon, Goesan-gun, Cheongcheon, Chungcheongbuk-do, Korea); 2) the Danyang population (Eosangcheon-myeon, Danyang-gun, Chungcheongbuk-do, Korea; and 3) the Hoengseong population (Anheung-myeon, Hoengseong-gun, Gangwon-do, Korea) during the spawning seasons of 2011 ~ 2014.
Standard length, egg size, and egg volume of A. signifer in the Hoengseong population were significantly larger than those of the other two populations: the Goesan population of A. signifer most preferred Lamprotula leai among the four mussels and the Danyang population was only possible to spawn in Unio douglasiae sinuolatus.
In comparison, ovipositor length, number of mature eggs, and egg size of A. signifer in the Goesan population were relatively greater than those of the Danyang and Hoengseong populations.
The Goesan population of A. signifer mainly inhabited areas with a high proportion of rocks, sand, and sandy clay and a relatively low proportion of pebbles and gravel. The Goesan population of A. signifer laid its eggs on gill chambers of four mussels existing sympatrically, including L. leai, U. d. sinuolatus, Anodonta arcaeformis flavotincta, and Lanceolaria grayana, but among them, the preference of A. signifer for mussels was dominantly L. leai which seemed to be close to its physical condition. The number of eggs, larvae, or both of A. signifer laid on L. leai increased at a higher density of the two species.
L. leai was the most preferred host mussels species of A. signifer, although there were some differences in the wild conditions at the Goesan population, experiment 1 in the Goesan population, and experiment 2 in the Danyang population. These results indicate that A. signifer seems to be a generalist in its use of mussels for oviposition rather than a specialist that makes use of a narrow range of mussels.
Some L. leai used inner and outer demibranches together as a glochidium brood pouch. A larger number of eggs, larvae, or both released by A. signifer appeared in mussels that had glochidium than those that did. The eggs, larvae, or both laid in L. leai by A. signifer were found at a similar frequency in the inner and outer demibranches but the post-larvae were showed a different result according to mussels that either had glochidium or not: for non-brooding mussels without glochidium, the post-larvae were found significantly more frequently in the inner than the outer demibranch and for brooding mussels that had glochidium, they were found in the outer rather than the inner demibranch.
The presence of the mussel may play an important role in inducing elongation of the female ovipositor, rather than affecting the bitterling male. The ovipositor of the female of A. signifer was periodically elongated and spawning was reduced to an interval of 4 ~ 6 days under the presence of the mussel. It took a mean 1.2 days to spawn in an aquarium, and the number of eggs laid in the mussels was about 4.8 per spawning.
A. signifer was widely distributed in Hangang River and most found in Namhangang River. Recent anthropogenic activities such as the stream improvement, environmental pollution, decreasing the host mussels, and dam construction have resulted in declining reasons of A. signifer. This fish prefers heavily vegetated stagnant pool that offers the sites for feeding activity and hiding place.
In the present study, A. signifer showed several host adaptations for ovipositor length, egg shape, and the number of mature eggs released in relation to a particular mussels species. The induction of elongation of the female ovipositor of A. signifer was highly likely related to the mussels. Also, we should prepare policy of protection to habitat and host mussels for conservation of A. signifer.