Larval fish stomach content database from Conception Bay, Newfoundland, Canada

The data for this study are from a sub-Arctic coastal ecosystem (1000 km2) in the northwest Atlantic. The aim of the collection was to characterize the prey of the larvae of important fish species that occur in Conception Bay, Newfoundland.

Plankton was sampled fortnightly from late May until late September in 1986 and 1987 at three locations on the eastern shore of Conception Bay (47°45′N, 53°00′W), Newfoundland, Canada. Ichthyoplankton were collected using a 0.75 m ring net, fitted with 165 μm nitex and a General Oceanics flow meter, and towed at a depth of 5-10 m at a speed of 0.3-0.5 m s-1 for 10 minutes. Zooplankton samples were obtained using a similar ring net fitted with 64 μm nitex which was towed along the same path immediately following ichthyoplankton sampling. Samples were preserved in 4% buffered formaldehyde. The sampling of zooplankton does not provide a good approximation of the density of potential prey < 65 μm), but post hoc analysis revealed this size category of prey represented a very small fraction of all prey items found in the guts of larval fish from this database (~ 2%). It is important to note that net sampling did not provide accurate estimates of the abundance of protists which may be important prey for some larval fish during early developmental stages although very few were found in stomach contents from this study, likely owing to preservation using formaldehyde.

All fish larvae were sorted and identified to the lowest taxonomic level possible, and individuals measured for standard length to the nearest millimeter using an ocular micrometer. Subsamples of larvae of 11 dominant species of fish were taken for stomach analysis (May – Stichaeus punctatus (Stichaeidae); July – Clupea harengus (Clupeidae), Gadus morhua (Gadidae), Hippoglossoides platessoides (Pleuronectidae), Myzopsetta ferruginea (Pleuronectidae), Pseudopleuronectes americanus (Pleuronectidae), Ulvaria subbifurcata (Stichaeidae), Liparis spp.(Liparidae); September – Mallotus villosus (Osmeridae), Glyptocephalus cynoglossus (Pleuronectidae), Tautogolabrus adspersus (Labridae)). Individual specimens used for stomach analysis were selected to ensure that observations of feeding from each species spanned the entire period of their seasonal occurrence. For each individual, the length of the maxilla (or jaw, where the maxilla had not formed) was measured to the nearest 10 µm, and the digestive tract was removed and teased apart using fine dissecting needles. Presence or absence of a yolk sac, and the state of digestion of stomach contents were noted.

Zooplankton samples (not reported here) were processed by removing the large organisms not contributing to the diet of larval fish (i.e., fish, medusae, pteropods and amphipods; Supplementary Table 1) and sieving through a 64 μm mesh, suspending in a calibrated beaker, and subsampling with a Hensen-Stempel pipette to yield a count of at least 500 organisms. Animals were identified to the lowest taxonomic level and stage possible and the body widths of five individuals of each species and life stage were measured to the nearest 5 μm. For animals with continuous growth, or that could not be identified to species, the width of each individual was measured to the nearest 10 μm.

Stomach contents were identified to the lowest taxonomic and life stage possible. A total of 17209 prey were enumerated and identified, ranging from 482 to 4989 (median = 1067) per fish species. If the item was unidentifiable, or if a species had continuous growth, specimen width was measured to the nearest 10 μm. Otherwise, the width was estimated from the means of subsamples of the taxa and stages identified from the zooplankton samples described above, to avoid distortions cause by partial digestion. Analyses of these data have been published by Pepin and Penney (1997), Pepin and Penney (2000) and Pepin (2022).

References Pepin, P. 2022. Feeding by larval fish: How taxonomy, body length, mouth size, and behaviour contribute to differences among individuals and species from a coastal ecosystem. Ices Journal of Marine Science, 80: 91-106. 10.1093/icesjms/fsac215

Pepin, P., and Penney, R. W. 1997. Patterns of prey size and taxonomic composition in larval fish: Are there general size-dependent models? Journal of Fish Biology, 51 (Supplemental A): 84-100. https://onlinelibrary.wiley.com/doi/10.1111/j.1095-8649.1997.tb06094.x

Pepin, P., and Penney, R. W. 2000. Feeding by a larval fish community: Impact on zooplankton. Marine Ecology Progress Series, 204: 199-212. https://www.int-res.com/articles/meps/204/m204p213.pdf