Does copepod size determine food consumption of particulate feeding fish?

van Deurs, M., Koski, M., and Rindorf, A. Does copepod size determine food consumption of particulate feeding fish? – ICES Journal of Marine Science, 71: . The climate-induced reduction in the mean copepod size, mainly driven by a decrease in the abundance of the large Calanus finmarchicus around 1987, has been linked to the low survival of fish larvae in the North Sea. However, to what extent this sort of reduction in copepod size has any influence on adult particulate feeding fish is unknown. In the present study, we investigated the hypothesis that the availability of the large copepods determines food consumption and growth conditions of lesser sandeel (Ammodytes marinus) in the North Sea. Analysis of stomach content suggested that food consumption is higher for fish feeding on large copepods, and additional calculations revealed how handling time limitation may provide part of the explanation for this relationship. Comparing stomach data and zooplankton samples indicated that lesser sandeel actively target large copepods when these are available. Finally, we observed that the length of lesser sandeel began to decrease in the late 1980s, simultaneously with the C. finmarchicus decline.

Intertidal life: field observations on the clingfish Gobiesox barbatulus in southeastern Brazil

The clingfish Gobiesox barbatulus shows nocturnal feeding activity, spending most part of the day stationary and adhered to the inferior part of stones. To feed, this species uses the sit-and-wait and particulate feeding tactics. It shows a carnivorous feeding habit mostly consuming small benthic crustaceans. It can move in two ways: (1) "stone-by-stone", sliding its ventral sucker disc across each stone and (2) "surf", when it takes advantage of the energy of the ebbing tide to quickly cross a distance up to four times its body length. Its reproductive season occurs between the end of spring and the beginning of summer, during which time it lays about 2,000 adhesive eggs of 1 mm each in a single layer under stones. It has more than one egg-laying session per reproductive season, therefore showing several different developmental stages. It performs fanning, mouthing and guarding of the eggs as forms of parental care. Data shown here also indicates that G. barbatulus has some shelter fidelity, being probably territorial.

Particle retention during respiration and particulate feeding in the suspension-feeding blackfish, Orthodon microlepidotus

Juvenile blackfish (Orthodon microlepidotus) retained styrene microspheres (30–90 μm) during respiration in the absence of food. The fish retained significantly more microspheres when particulate feeding on Artemia adults, suspension feeding on Artemia nauplii, or in the presence of Artemia extract than when respiring in the absence of food. The frequency distribution of microsphere sizes retained during respiration did not differ significantly from that retained during feeding, a result that is consistent with the hypothesis that the site and method of particle retention during respiration and particulate feeding do not differ from those operating during suspension feeding. There was significant interindividual variability in the number of particles retained. Some individuals retained consistently fewer microspheres than other individuals of similar size and age, suggesting that further study is needed to quantify interindividual variation in other factors (e.g., stroke volume, ventilation rate, or mucus secretion) that have the potential to affect particle retention rates. Our results have implications for the energetics of suspension-feeding fishes, the impacts of suspension-feeding fishes on plankton communities, and the exposure of these fishes to toxic phytoplankton strains and particle-bound organic chemicals.

Use of the lateral line in particulate feeding in the dark by juvenile alewife (Alosa pseudoharengus)

The alewife (Alosa pseudoharengus) is an obligate planktivore which uses a variety of methods for capturing zooplankton. Alewife eat Mysis relicta, especially larger individuals, at night during a vertical migration by both predator and prey. We proposed and tested the hypothesis that alewife use the lateral line to sense prey and feed particulately (single prey at a time) in the dark. We used Daphnia magna and Artemia salina adults as prey. Prey densities were such that they did not elicit filter feeding. Observations using infrared video showed that alewife captured individual prey and bit at a vibrating inert bead. We concluded that under appropriate conditions, alewife were size selective and that streptomycin (which blocks the lateral line sensory cells) eliminated this feeding behavior.