Number Of Opaque Zones Research Articles

Mating system and protandrous sex change in “Magochi” Platycephalus sp. 2 (Platycephalidae)

In this study we investigated sex change and the mating system of a platycephalid fish, Platycephalus sp. 2 (Japanese name: Magochi), found in Japanese waters. Among 202 specimens from Tateyama, Chiba, Japan, obtained in 2014 and 2015, histological observation of the gonads distinguished 103 females, 97 males and two hermaphrodites (individual with both ovarian and testicular parts). Females were significantly larger than males. In a rearing experiment conducted with six males and three females, only the smallest male changed sex to female, thereby revealing protandry in this species. In field observations, seven males and eight females appeared throughout the study period. During pairing, a male would follow a female on the sandy bottom. The mating system of this species has been regarded as random mating based on temporal pair bonding, no territoriality, and no size-assortative mating, which correspond well with the size-advantage model. In a previous study Platycephalus sp. 2 was regarded as a gonochore, with a higher growth rate for females than males. Thus, females should be larger than males. In the present study, there was no significant difference in age between the sexes, as estimated from the number of opaque zones in sagitta otoliths. Overall, these findings indicate that there are primary females and males without sex change. Thus, protandrous and gonochoristic individuals may co-exist in populations of Platycephalus sp. 2.

Age and Stock Analysis Using Otolith Shape in Gags from the Southern Gulf of Mexico

AbstractOn Campeche Bank (CB) in the southern Gulf of Mexico, Gags Mycteroperca microlepis are captured as part of a sequential multispecies fishery. Limited scientific data suggest that the Gag is the third most important commercial species in the region, contributing 21% (total weight) of the overall grouper catch. Neither age nor stock data are currently available for Gags in this region, making it impossible to determine how this species is affected by current fishing practices. Such information is vital for the CB stock since it acts as a genetic source for a mixed Gag population on the west Florida shelf through a constant unidirectional flow of larvae. The goal of this study was to generate baseline age and stock structure data for Gags on CB. Age was quantified from otoliths by counting the number of annuli (indicated by the number of opaque zones from the otolith core to the margin) in thin sections. Otolith shape was analyzed by using discrete wavelet transforms, linear otolith morphometrics, and shape indices. In each of 198 specimens, age was determined based on examination of the right sagittal otolith, and shape analysis was conducted on the left sagittal otolith. Individual age ranged from 4 to 17 years, and otolith opaque band deposition occurred annually between December and February. Using principal components analysis and linear discriminant analysis, two distinct groups were identified (discrimination success = 98%), indicating the presence of substructure in the CB stock of Gags. Otolith analysis clearly assisted in achieving a better understanding of the CB Gag stock and in identifying the complexity within the stock, demonstrating that otolith analysis is a useful tool in characterizing fish populations. The study results highlight the urgent need for Gag stock assessment in this region and for the application of a cautious approach to fishery management given the immense gaps in biological data for this species.Received January 13, 2016; accepted July 18, 2016 Published online October 7, 2016

Age and growth of two endemic flatfish (Colistium guntheri and C. nudipinnis) in central New Zealand waters

Brill (Colistium guntheri) and turbot (C. nudipinnis) were aged by counting opaque growth zones in whole and sectioned otoliths. Zones counts from whole otoliths under-estimated age compared with counts from thin otolith sections. Other species of flatfish that have previously been aged from whole otoliths should be re-examined for evidence of age under-estimation, which may be common in species with thick otoliths. Marginal analysis of thin sections supported the hypothesis that one translucent and one opaque zone are formed each year in brill aged 5–10-years old. Marginal analyses for brill greater than 10 years of age, and for turbot, were inconclusive. However, 2+ and 3+ captive-reared turbot deposited the expected number of opaque zones from hatching. Both species grow rapidly for the first three years of life before growth slows appreciably. Turbot grow faster and larger than brill, and females grow faster and larger than males in both species. Growth is minimal in fish older than five years. Maximum observed ages were 21 years for brill and 16 years for turbot.