Three lineages of cartilaginous fishes have independently evolved filter feeding (Lamniformes: Megachasma and Cetorhinus, Orectolobiformes: Rhincodon, and Mobulidae: Manta and Mobula); and the structure of the branchial filters is different in each group. The filter in Rhincodon typus has been described; species within the Lamniformes have simple filamentous filters, but the anatomy and ultrastructure of the branchial filter in the mobulid rays varies and is of functional interest. In most fishes, branchial gill rakers are elongated structures located along the anterior ceratobranchial and/or epibranchial arches; however, mobulid gill rakers are highly modified, flattened, lobe-like structures located on the anterior and posterior epibranchial elements as well as the ceratobranchials. The ultrastructure of the filter lobes can be smooth or covered by a layer of microcilia, and some are denticulated along the dorsal and ventral lobe surface. Flow through the mobulid oropharyngeal cavity differs from other filter-feeding fishes in that water must rapidly deviate from the free stream direction. There is an abrupt 90° turn from the initial inflowing path to move through the laterally directed branchial filter pores, over the gill tissue, and out the ventrally located gill slits. The deviation in the flow must result in tangential shearing stress across the filter surface. This implies that mobulids can use cross-flow filtration in which this shearing force serves as a mechanism to resuspend food particles initially caught by sieving or another capture mode. These particles will be transported by the cross filter flow toward the esophagus. We propose that species with cilia on the rakers augment the shear mediated movement of particles along the filter with ciliary transport.

Experimental and computational fluid dynamics indicate that manta rays use a novel filtration mechanism for feeding.

The four, evolutionarily independent, lineages of suspension feeding elasmobranchs have two types of branchial filters. The first is a robust, flattened filter pad akin to a colander (e.g., whale sharks, mantas and devil rays) while the second more closely resembles the comb-like gill raker structure found in bony fishes (e.g., basking and megamouth sharks). The structure and the presence of mucus on the filter elements will determine the mechanical function of the filter and subsequent particle transport. Using histology and scanning electron microscopy, we investigated the anatomy of the branchial filters in 12 of the 14 species of Chondrichthyian filter-feeding fishes. We hypothesized that mucus producing cells would be abundant along the filter epithelium and perform as a sticky mechanism to retain and transport particles; however, we found that only three species had mucus producing goblet cells. Two of these (Mobula kuhlii and Mobula tarapacana) also had branchial cilia, indicating sticky retention and transport. The remaining filter-feeding elasmobranchs did not have a sticky surface along the filter for particles to collect and instead must employ alternative mechanisms of filtration (e.g., direct sieving, inertial impaction or cross-flow). With the exception of basking sharks, the branchial filter is composed of a hyaline cartilage skeleton surrounded by a layer of highly organized connective tissue that may function as a support. Megamouth sharks and most of the mobulid rays have denticles along the surface of the filter, presumably to protect against damage from large particle impactions. Basking sharks have branchial filters that lack a cartilaginous core; instead they are composed entirely of smooth keratin.

SUMMARYWe created physical models based on the morphology of ram suspension-feeding fishes to better understand the roles morphology and swimming speed play in particle retention, size selectivity and filtration efficiency during feeding events. We varied the buccal length, flow speed and architecture of the gills slits, including the number, size, orientation and pore size/permeability, in our models. Models were placed in a recirculating flow tank with slightly negatively buoyant plankton-like particles (~20-2000m) collected at the simulated esophagus and gill rakers to locate the highest density of particle accumulation. Particles were captured through sieve filtration, direct interception and inertial impaction. Changing the number of gill slits resulted in a change in the filtration mechanism of particles from a bimodal filter, with very small (≤50m) and very large (>1000m) particles collected, to a filter that captured medium-sized particles (101-1000m). The number of particles collected on the gill rakers increased with flow speed and skewed the size distribution towards smaller particles (51-500m). Small pore sizes (105 and 200m mesh size) had the highest filtration efficiencies, presumably because sieve filtration played a significant role. We used our model to make predictions about the filtering capacity and efficiency of neonatal whale sharks. These results suggest that the filtration mechanics of suspension feeding are closely linked to an animal's swimming speed and the structural design of the buccal cavity and gill slits. Supplementary material available online at

We present genetic and morphometric support for a third, distinct, and recently diverged group of Manta ray that appears resident to the Yucatán coastal waters of the Gulf of Mexico. Individuals of the genus Manta from Isla Holbox are markedly different from the other described manta rays in their morphology, habitat preference, and genetic makeup. Herein referred to as the Yucatán Manta Ray, these individuals form two genetically distinct groups: (1) a group of mtDNA haplotypes divergent (0.78%) from the currently recognized Manta birostris and M. alfredi species, and (2) a group possessing mtDNA haplotypes of M. birostris and highly similar haplotypes. The latter suggests the potential for either introgressive hybridization between Yucatán Manta Rays and M. birostris, or the retention of ancestral M. birostris signatures among Yucatán Manta Rays. Divergence of the genetically distinct Yucatán Manta Ray from M. birostris appears quite recent (<100,000 YBP) following fit to an Isolation-with-Migration model, with additional support for asymmetrical gene flow from M. birostris into the Yucatán Manta Ray. Formal naming of the Yucatán Manta Ray cannot yet be assigned until an in-depth taxonomic study and further confirmation of the genetic identity of existing type specimens has been performed.

When feeding, most aquatic organisms generate suction that draws prey into the mouth. The papers in this volume are a demonstration of this fact. However, under what circumstances is suction ineffective as a feeding mechanism? Here we consider the interplay between suction, ram, and biting, and analyze the contribution of each to the capture of prey by a wide variety of species of fish. We find, not surprisingly, that ram is the dominant contributor to feeding because suction, and biting, are only effective when very close to the prey. As species utilize more strongly ram-dominated modes of feeding, they may be released from the morphological and behavioral constraints associated with the need to direct a current of water into the head. Morphological and behavioral changes that facilitate larger gapes and stronger jaws are explored here, including predators that lack a protrusile upper jaw, predators with elongate jaws, predators that rely on suspension feeding, and predators that bite. Interestingly, while the mobility of the jaws and the shape of the opening of the mouth are modified in species that have departed from a primary reliance on suction feeding, the anterior-to-posterior wave of expansion persists. This wave may be greatly slowed in ram and biting species, but its retention suggests a fundamental importance to aquatic feeding.

Parents in academic careers face notable challenges that may go unrecognized by university management and/or policy makers. The COVID-19 pandemic has shed light on some of these challenges, as academic parents shifted to working from home while simultaneously caring for children. On the other hand, many parents found that the shift to working from home offered new opportunities such as working more flexible hours, development of digital skillsets, and increased involvement in the education of their children. In this article we explore the work-related challenges and opportunities experienced by academic parents as a result of the COVID-19 pandemic and offer potential long-term solutions for academic parents and their universities. We use the following methods: (1) a literature review focused on identifying the work-related challenges academic parents faced prior to the pandemic, as well as the impact of the pandemic on scientists and working parents and (2) administer a world-wide survey with the goal of identifying the challenges and opportunities associated with parenting and academic work through the COVID-19 lockdown (304 total responses; 113 complete). Moving forward these findings have enabled conclusions to be drawn in order to shape a new normal. Our aim is to offer university administrators, policy makers, and community service providers with ways to provide additional support for academic parents as well as provide tools for academic parents to learn successful strategies directly from their peers.

Hyperostosis, excessive bone growth along bone that stems from bone, periosteum or articular or epiphyseal cartilage, occurs in at least 22 families of fishes most of which are tropical or subtropical marine species. While the presence of hyperostosis is well documented in fishes, the mechanism driving the development of the excessive bone growth is unclear. This study documented hyperostosis along the dorsal pterygiophores in both sexes of oarfish, Regalecus russellii; however, it was not present in all specimens examined. This is the second lampridiform fish with hyperostoses and the first case documented in a deeper-water, epi-mesopelagic fish. In oarfish, the majority of the dorsal pterygiophores tissues are poorly mineralized, anosteocytic bones with some fish displaying localized stiffened, hyperostotic growths near the distal edge. Oarfish lack a swim bladder so they must continuously beat their bi-directional dorsal fin to maintain position within the water column while engaged in locomotory behavior. These fishes have areas of localized, hyperostotic skeletal elements along the dorsal pterygiophores that, presumably, function as a stiffened lever system to support fin undulation. It was noted that hyperossification was not present in all fish examined and was only documented in fish with total lengths greater than 3 m.