Albinism in fish is a rare trait and unreported in syngnathids, and its occurrence in a species may carry ecological implications as well as value for the ornamental fish trade. A reproductive study based on a breeding pair of Hippocampus reidi Ginsburg, 1933, a vulnerable species used in aquarium and traditional medicine, was conducted under controlled conditions in a marine aquarium. Here we detail the first occurrence of albinism in H. reidi. It was identified that a F2 inbreeding generates an average of 24±1.4% of albino seahorses. Melanophore counts and histological sections confirmed albinism in the third generation of seahorses. Our results are interesting to aquaculture since a new variety opens a new venue for the ornamental trade and may highlight new insights concerning inbreeding in small natural populations. Additionally, an albino lineage can provide valuable insights into the role of pigmentation in physiological and ecological contexts that have not yet been evaluated for H. reidi and other syngnathids.
The F2 couple generated an average offspring around 252±52 pigmented and 79±10 of non-pigmented fish in three recorded births. The produced lineages had an average of 24±1.4% of albinos, without pigmented melanophores. Meanwhile pigmented seahorses have 16.2±1.8 melanophores in the head and 21.5±2.1 in the trunk area (500 µ²). Even with the aid of a microscope, it was not possible to observe melanophores, or any other chromatophores, along the body of albino individuals (Figure 1). Hematoxylin and eosin staining revealed that, in pigmented individuals, melanophores are clearly present in the skin, along with a thick layer of melanin in the pigmented epithelium of the retina (Figure 2 A and C). Additionally, the retina lacks a pigmented epithelial layer (Figure 2 B and D). Thus, a third-generation inbreeding may generate albino H. reidi seahorses. This variation is already known to be profitable for the ornamental trade. This lineage can also provide important insights into the role of pigmentation in physiological and ecological contexts that have not yet been evaluated for the species and other syngnathids. Therefore, more studies should aim the successful rearing of this variety and investigate the genetic alterations needed for this trait to be expressed.