X-ray measurements of gill-arch movements in filter-feeding bream, Abramis brama (Cyprinidae)

The technique of X-ray cinematography was used to study pharyngeal movements in Abramis brama (L.). The theoretical and practical problems in X-ray cinematography of feeding fish are discussed, as well as criteria for the selection of images suited for detailed measurements.
Respiration and filter-feeding on Daphnia pulex (length c . 1 mm) show different gill arch movement patterns in bream. Slits between gill-arches are kept smaller during filter-feeding. In addition, during filter-feeding, this inter-arch distance decreases considerably in a posterior direction. The hypothesis that particle retention occurs on the slits formed between adjacent gillarches and their gill-rakers is not supported by the present results.     

Making a master filterer: Ontogeny of specialized filtering plates in silver carp (Hypophthalmichthys molitrix)

Filter feeding fishes possess several morphological adaptations necessary to capture and concentrate small particulate matter from the water column. Filter feeding teleosts typically employ elongated and tightly packed gill rakers with secondary bony or epithelial modifications that increase filtering efficiency. The gill rakers of Hypophthalmichthys molitrix, silver carp, are anatomically distinct from and more complex than the filtering apparatus of other teleostean fishes. The silver carp filtering apparatus is composed of biserial, fused filtering plates used to capture particles ranging in size from 4 to 80 μm. Early in ontogeny, at 15–25 mm standard length (SL), silver carp gill rakers are reminiscent of other more stereotypical teleostean rakers, characterized by individual lanceolate rakers that are tightly packed along the entirety of the branchial arches. At 30 mm SL, secondary epithelial projections and concomitant dermal ossification begin to stitch together individual gill rakers. During later juvenile stages, dermal bone further modifies the individual gill rakers and creates a bony scaffold that supports the now fully fused and porous epithelium. By adulthood, the stitching of bone and complete fusion of the overlying epithelium creates rigid filtering plates with morphologically distinct faces. The inner face of the plates is organized into a net‐like matrix while the outer face has a sponge‐like appearance comprised of differently sized pores. Here, we present morphological data from an ontogenetic series of the filtering apparatus within silver carp. These data inform hypotheses regarding both how these gill raker plates may have evolved from a more basal condition, as well as how this novel architecture allows this species to feed on exceedingly small phytoplankton, particles that represent a greater filtering challenge to the typical anatomy of the gill rakers of fishes.     

Patterns and repeatability of multi-ecotype assemblages of sympatric salmonids

Aim

High repeatability among assemblages of closely related but ecologically distinct ecotypes implies predictability in evolution and assembly of communities. The conditions under which ecotype assemblages form predictably, and the reasons, have been little investigated. Here, we test whether repeatability declines as the number of ecotypes builds.

Location

Postglacial lakes with a circumboreal distribution.

Time Period

Data were extracted from studies published between 1982 and 2019.

Major Taxa Studied

Ecotype assemblages from two Salmonid genera – Salvelinus and Coregonus. Fish in postglacial lakes commonly occur as pairs of ecotypes, typically with a pelagic and a littoral/benthic form, but in Salvelinus and Coregonus, assemblages commonly contain multiple sympatric ecotypes.

Methods

We used a meta-analysis of Salvelinus and Coregonus to empirically assess how repeatability varies across assemblages of two to seven ecotypes. We examined repeatability of use of broad niche categories as well as underlying phenotypic traits.

Results

Within Coregonus, repeatability across multi-ecotype assemblages did not break down with the addition of a third or fourth ecotype. However, in Salvelinus, repeatability was largely absent and independent of the number of ecotypes. Repeatability of trait frequency distributions was absent in both genera, yet associations between trait means and niche categories were evident, especially in Coregonus.

Main Conclusions

These results show that repeatability can vary greatly between lineages; that repeatability need not break down as the number of ecotypes builds; and that high repeatability of broad niche categories may result despite marked differences in the underlying frequency distribution of trait means. These findings not only affirm the presence of repeatable ecotype assembly and early stages of divergence in postglacial fishes at a global scale, but also highlight variability among taxa and underlying phenotypic traits.     

Adaptations of fish species to oxygen depletion in a central Amazonian floodplain lake

Pronounced seasonal and daily oxygen concentration changes are characteristic for Amazonian floodplain lakes. Studies on the fish fauna of the Lago Camaleão, Solimões River, Amazonas, Brazil, showed several fish species which are able to survive prolonged periods of heavy hypoxia. Twenty species belonging to eight families were observed in the laboratory in order to determine their respiratory adaptations to hypoxic conditions and oxygen concentrations at which the fish present respiratory adaptations. Finally, the fish species were distributed throughout the habitats of Lake Camaleão according to their adaptation responses. Ten fish species used the surface water for aquatic surface respiration, four species used atmospheric oxygen for aerial respiration, four species used oxygen supplied by the exudation of the roots of floating macrophytes and two exhibited a high tolerance to hypoxic conditions, and well-developed physiological biochemical mechanisms. The fish fauna is well adapted to low oxygen concentrations. The large variety of morpho-anatomical adaptations associated with biochemical and physiological mechanisms to tolerate hypoxic and anoxic conditions enable the 20 fish species to exploit several habitats of Lago Camaleão, such as floating aquatic macrophyte meadows, open water and near the shoreline.     

Spatial arrangement of fish gill secondary lamellar cells in intact and dissociated tissues from rainbow trout (Oncorhynchus mykiss) and Atlantic salmon (Salmo salar)

Gill structure of rainbow trout and Atlantic salmon was investigated using cell disaggregation and dry fracture techniques for scanning electron microscopy (SEM), allowing new interpreta-tions of the structure of the secondary lamella. The basement membrane underlying the lamellar epithelium (secondary epithelium) was shown to be a tough sheet with numerous depressions corresponding to underlying pillar cells. This membrane is probably the most important structural element of the secondary lamella, capable of withstanding considerable mechanical stress. For the first time the structure of the apical surface of the secondary lamella was shown by SEM to consist of an outer microridged coat overlying a fibrous coat which appears continuous with the extracellular matrix surrounding the rest of the cell. When cells were detached they rounded up and the external microridged coat became more vesicle like, indicating the labile nature of this coat. In cell suspension preparations, epithelial, mucus and chloride cells are present as well as many blood derived cells such as erythrocytes, presumptive leucocytes and thrombocytes.