The feeding habits and reproductive biology of red-toothed triggerfish Odonus niger (Ruppell, 1836) was analysed from 449 specimens collected from the Karnataka coast of the south-eastern Arabian Sea. Of the total stomachs examined, only 54 (12%) were empty and 395 contained food remains. The diet comprised crustacean remains (48.0%), zooplankton (21.4%), algae (16.5%), fish remains (6.1%) and cephalopod remains (5.3%) along with partially digested matter (2.3%) and detritus (0.4%). The species was found to be a generalist feeder and an omnivore. The overall sex ratio between males and females (1: 0.44) was significantly (P < 0.05) different. Histological examination of the ovaries indicated asynchronous ovarian development in females, with males maturing earlier than females. The gonadosomatic index (GSI) patterns of males and females, and the presence of ripe ovaries and spermatozoids suggested that April–May is the peak spawning period. The absolute and relative fecundity estimates ranged from 16,464–312,420 eggs and 251–2812 eggs g−1 respectively. Fecundity was positively correlated with total length and body weight. The biological information on diet composition and reproductive traits provided for the first time in this study can facilitate conservation, management and sustainable exploitation of this species in the study area.
Aim: The study aimed to investigate the morphometric and meristic measurements, length-weight relationship and relative condition factor of Odonus niger landed along coastal Karnataka. Methodology: The morphometric and meristic measurements, length-weight relationship and relative condition factor (Kn) of O. niger was studied for a period of eight months from August 2019 to March 2020. The different morphometric characters were subjected to statistical analysis. The length-weight relationship was analyzed for both the sexes (female and male) and combined data. Monthly relative condition factor was analyzed for both the sexes and for different size group. Results: A comparison of different morphometric measurements exhibited good extent of correlation indicating good extent of interdependence of these characters. Four out of eight morphometric characters are environmentally controlled and suggested wide range of zoogeographical distribution of O. niger. The length-weight relationship is indicated as W = 0.046 L2.565, W = 0.044 L2.589 and W = 0.047 L2.561 with coefficient of determination (r2) of 0.910, 0.913 and 0.910 for male, female and combined sexes, respectively. The 'b' values of both the sexes (male and female) exhibited negative allometric growth (p<0.05) and appeared to be leaner. There was no significant (p<0.05) variation for relative condition factor (Kn) among the months and size groups. However, little higher values were observed during November and February. Interpretation: The study fills the knowledge gap and support for developing a suitable management system for this fish species.
Summary
The present study aims to assess the seasonal and sex‐wise variations in proximate composition, amino acid profile and protein quality of Odonus niger, which will be the first report for this species. High‐protein (15.15%–20.05%) and low‐fat contents (0.46%–1.94%) were observed for the species studied. The highest protein was observed in September and December for male and female fishes respectively. The total essential amino acid (TEAA) content was 58.65–77.41 mg g−1 (males) and 60.25–77.38 mg g−1 (females) and leucine was the predominant EAA in both the sexes. The EAA index and biological value ranged between 17.50–22.56 and 7.38–12.89 for males and 18.02–22.48 and 7.94–12.80 for female fishes respectively. In male, TEAA followed Sept>Jan > Dec > Aug > Oct > Nov and in female it was Oct > Sept>Dec > Nov > Aug > Jan. The chemical score for histidine and threonine was more than the FAO recommended values. Overall, the nutritional quality of this unconventional species proved very good and comparable with other commercially important lean fishes.
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