Growth and reproduction in mesopelagic fishes: a literature synthesis

Abstract

The mesopelagic zone covers a vast expanse of the World’s oceans and contains some of the most abundant vertebrates on the planet. This midwater region is central to the transfer of energy and carbon between the atmosphere and the deep, yet there are large knowledge gaps in our understanding of the life history of its animals. Here we synthesize the current state of knowledge of research on age, growth, and reproduction of mesopelagic fishes, the basic biological information fundamental to understanding the population dynamics of species in this ecosystem. Collectively, two-thirds of life history research on mesopelagic fishes has been undertaken on myctophids, yet many other abundant and important groups are lacking research. There are generally hotspots of mesopelagic fish research mostly centred in the northern hemisphere, with little to no coverage in the Indo-Pacific region nor the poles. Furthermore, the effects of some anthropogenic stressors—chiefly climate change and resource extraction—on the life history of the animals in this zone is uncertain and needs to be considered. Knowledge of growth and reproduction are key traits required for a holistic assessment and understanding of this ecosystem, and hopefully this synthesis will provide a springboard for greater focus in this area.

Mesopelagic–epipelagic fish nexus in viability and feasibility of commercial‐scale mesopelagic fisheries

“…The harvest of mesopelagic fish may lead to increases in the stocks of some predators (e.g., grenadiers) and decreases in others (e.g., longspine thornyhead) (Dowd et al, 2022). Indeed, the mesopelagic group is not homogeneous, and mesopelagic fishes vary in growth and reproduction (Caiger et al, 2021).…”

Intraspecific variability of the saccular and utricular otoliths of the hatchetfish Argyropelecus hemigymnus (Cocco, 1829) from the Strait of Messina (Central Mediterranean Sea)

“…Mesopelagic fishes show a great abundance in biomass, being the main component of the deep scattering layer (DSL) and mesopelagic zone, and the most abundant vertebrates on earth for their density and diffusion in all the Oceans [55,56]. Several studies have been focused worldwide on these species' distribution, biology, biodiversity and ecology [51,[56][57][58][59], also investigating morphology, microstructures and growth of sagittae [57,[60][61][62][63][64][65]. Despite this, the knowledge base on mesopelagic fishes remains scarce, with several gaps regarding the biology and eco morphology of many species and families.…”

“…According to previous studies performed in the Strait of Messina [70,71], A. hemigymnus is among the most numerically relevant species for abundance and frequency of stranding during the entire year. This large number of available specimens is useful to obtain information on the eco-morphological adaptations and life history of this species due to the high interregional variability of life histories in mesopelagic teleost [59,93]. Therefore, obtaining new data on hathcetfishes' saccular and utricular otoliths' morphology and intra-specific variability, applying techniques never applied before on this species, such as SEM and shape analysis, is essential to improve the knowledge base on this rare and still poorly studied mesopelagic teleost, exploring ecomorphological adaptation to deep marine habitats.…”

Distribution and densities of fish larvae species with contrasting life histories as a function of oceanographic variables in the deep-water region of the southern Gulf of Mexico

“…However, fecundity is typically lower in oceanic species than in neritic species [ 16 – 18 ]. Meso- and bathypelagic species’ spawning occurs mainly above 500 m (see [ 19 , 20 ]), and eggs are fertilized as they rise to a specific vertical position in the water column as a function of the lipid and protein content of the yolk sac [ 16 , 21 , 22 ]. The larval stage of many mesopelagic species lasts ~ 50 days [ 23 , 24 ].…”