Abstract
The barred sand bass Paralabrax nebulifer is a commercially important fish off the west coast of Baja California Sur. To assess the diet of this species and variations as a function of sex and reproductive condition, 60 specimens were captured using traps during seven seasonal sampling trips from August 2016 to August 2018 in an adjacent area to Magdalena Bay, Baja California Sur, Mexico. The stomach contents of 50 specimens were obtained (23 males and 27 females). Sex was diagnosed by direct observation of the gonads. Based on the gonadosomatic index, hepatosomatic index, and histological analyses, the reproductive season of the barred sand bass was corroborated for August 2016, April, August, and September 2017, and August 2018, and the non-reproductive season was corroborated for November 2016 and March 2018. The Index of Relative Importance (IRI) was used to classify the main diet components, which comprised three fish species, seven crustacean species, and one mollusk species. According to the IRI, the South American pilchard Sardinops sagax and the red pelagic crab Pleuroncodes planipes were the prey that contributed the most (55%) to the barred sand bass diet. The ANOSIM showed that there were significant differences in the amount and type of prey consumed by sex; the SIMPER analysis revealed that the species contributing the most to differences between the sexes were S. sagax (16.58%), Euphylax dovii (15.95%), Stenocionops ovata (12%), and P. planipes (11.82%) for females. There were significant differences in the amount and type of prey consumed between types of reproductive season; the species contributing the most to differences between seasons were Anchoa spp. (27.76%), and P. planipes for non-reproductive season (22.67%), and S. sagax (11.08%) for reproductive season. The feeding strategy of the barred sand bass was that of a specialist carnivorous predator that fed mainly on the fish Sardinops sagax during the reproductive season, which supply the dietary nutritional requirements of the lipids HUFA (arachidonic acid, 20:4n-6; eicosapentaenoic acid, 20:5n-3; docosahexaenoic acid, 22:6n-3), nutrients required to achieve reproductive success.
Highlights
Changes in the amplitude and phasing of seasonally varying processes can significantly affect the functioning of marine ecosystems, from primary producers to fish stocks (Beare & McKenzie 1999, Bograd et al 2002)
According to the histological analyses, in August 2016, the female gonad was at a very advanced vitellogenesis, since it was even possible to observe the migration of the germinal vesicle, which corresponds to the developing phase (Fig. 2A); whereas the variety and diversity of the spermatic cells of the male gonad corresponded to the developing phase (Fig. 2B)
In September 2017, in the female gonad, postovulatory follicles (Pof) were observed in the stroma and cells at the nucleolus chromatin stage (N) were abundant, which indicates the end of the spawning period, mature oocytes were observed in the rest of the section, so it was characterized as the spawning capable phase (Fig. 3C); the male gonads showed residual spermatozoa, to the extent that their own seminiferous tubules had lost their shape due to the large amount of sperm inside them; this was considered the spawning capable phase (Fig. 3D)
Summary
Changes in the amplitude and phasing (i.e., phenology) of seasonally varying processes can significantly affect the functioning of marine ecosystems, from primary producers to fish stocks (Beare & McKenzie 1999, Bograd et al 2002). Reproductive success must be strictly adapted to seasonal events in the environment, whether such fluctuations are the result of cyclical seasonal variations or migrations during the natural life cycle of some species. In those with seasonal reproduction, an important adaptation refers to the spawning time, which is adjusted in such a way that the specific feeding needs of the larvae coincide with the seasonal availability of food (Yamahira 2004, Jalabert 2005). Data on the ecobiology of each species of interest in its natural environment may be very useful in creating adequate culture conditions, leading to reproductive maturation and spawning (Mylonas et al 2010)
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