Use of natural markers to study population structure and migratory environmental history of Mugil cephalus L. in the coastal waters of Taiwan
Date Issued
2009
Date
2009
Author(s)
Hsu, Chih-Chieh
Abstract
To understand the population structure and migratory environmental history of flathead mullet Mugil cephalus in the costal waters of Taiwan, the allele frequency of 9 microsatellites loci of the mullet was analyzed and the elemental composition in otolith of the mullet was analyzed by LA-ICP-MS. The specimens of the mullet were collected from the spawning grounds in Northeastern (NE) and Southwestern (SW) waters of Taiwan, Tanshui River and Kaoping River estuary in 2005 ~ 2008, respectively. In addition, to validate the annulus in the scale and otolith of the mullet, the known-age cultured mullet were collected from two fish farms in Yunlin prefecture, western Taiwan. After collection, the morphometric characteristics including length and weight of the mullet were measured, and the scale, otolith, muscle tissue and gonad tissue were collected. he results revealed that: 1) Annuli in both scale and otolith of the cultured mullet were consistent with their true ages. 2) The mullet in the NE waters matured and spawned in mid-December as indicated by gonadosomatic index, fecundity, oocyte diameter frequency, and the maturation stages of gonad cell, which were all similar to those of the mullet that migrated to the SW waters at the same time. This indicated that the NE waters was also one of the spawning grounds of M. cephalus in the coastal waters of Taiwan. 3) The microsatellites indicated that there are three different populations (P1, P2, and P3) co-existed in the coastal waters of Taiwan. The contributions of the three populations were different among areas, in both spawning grounds, they were P1: 94%, P2: 1% and P3: 5%. The population genetic structure of the mullet in Kaoping River was different from those in NE and SW waters, which were mainly composed of P2 (30%) and P3 (62%). The growth rate and morphological variables were not significantly different among three populations. This suggested that growth rate and morphological variables can not be used as an indicator to distinguish the population units of M. cephalus in the coastal waters of Taiwan. 4) The Sr/Ca ratios in the otolith edges were significantly different for the mullet collected among sea water, estuary and freshwater (ANOVA, p < 0.05). The mean Sr/Ca ratios in otolith are lower than 3.2 × 10-3 when mullet lived in freshwater environment, larger than 6.0 × 10-3 when mullet lived in sea water environment. 5) Based on the Sr/Ca ratio in the otolith core region, the mullet was divided into three types: Type I, the mean Sr/Ca ratio was greater than 6.0 × 10-3, indicating that the mullet at early stage lived in sea water. Type II, the Sr/Ca ratio between 3.2 × 10-3 ~ 6.0 × 10-3, indicating that mullet at early stage lived in brackish water. Type III, the Sr/Ca ratio was less than 3.2 × 10-3, indicating that the mullet at early stage lived in freshwater environment. 6) The temporal change of Sr/Ca ratios in the otolith indicated that the migratory environmental histories of the mullet are similar among the 3 populations. n conclusion, the population genetic structures analyses indicated that M. cephalus in the coastal waters of Taiwan were not only the well-known migratory population which spawned in NE and SW waters of Taiwan, but also there were two more populations to be found in the Kaoping River estuary. Although these populations seemed to have different genetic structures but they can not be distinguished by morphology and growth rate. The difference in population genetic structure and non-differences in morphologic characteristics and life history strategies might be resulting from coexistence because of inhabitating the same or overlapping geographic areas.
Subjects
Mugil cephalus
microsatellites
population genetic structure
otolith microchemistry
migratory environment
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