Early life history of a seahorse, Hippocampus mohnikei, in Tokyo Bay, Japan
2001
Kanou, K. (Tokyo Univ. (Japan)) | Kohno, H.
The early morphological development, seasonal and spatial occurrence patterns, and food habits of a seahorse, Hippocampus mohnikei, in offshore waters of Tokyo Bay, central Japan, were studied on the basis of 206 juvenile and young specimens (6.0-65.3 mm TL) collected between August 1995 and January 1999. All the specimens were collected within the period from May to January, inclusive, each year. In the least developed specimen (6.0mm TL), the number of dorsal, anal, and pectoral fin rays had attained the adult complement, whereas the minute caudal fin, consisting of two rays, was present in juveniles of 6.0-26.4 mm TL. Hippocampus mohnikei >=35mm TL, being larger than settlement size (ca. 30mm TL), had very low gut fullness index values (GFI = 0, > 70% of specimens), whereas those of 15-29mm TL had higher values (GFI = 2-4, > 80% of specimens). In addition, larer indivikuals selectively fed on larger planktonic animals (species of Brachyura), which occurred naturally at low densities, although smaller food items, such as Oithona davisae and Penilia avirostris, occurred abundantly, being consumed by smaller H. mohnikei individuals (15-34mm TL). These results indicated that food availability for H. mohnikei in offshore waters of Tokyo Bay is significant for individuals larger than settlement size, because their food preference would shift from smaller food items to larger food items, which would be scarce in their environments.
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