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Fish diversity and ecology in the ocean’s mesopelagic zone are understudied compared to other marine regions despite growing interest in harvesting these potential resources. Otoliths can provide a wealth of taxonomic and life history information about fish, which can help fill these knowledge gaps; however, there has been relatively little research to date on the otoliths of mesopelagic species. Here, a species-specific image library was assembled of sagittal otoliths from 70 mesopelagic fishes belonging to 29 families collected in the western North Atlantic Ocean. Images of adult sagittal otoliths from 12 species were documented and photographed for the first time. The fish were identified to species with a combination of morphological characters and DNA barcoding. Regressions between otolith size and fish length are presented for the six species with the largest sample sizes in this study. This otolith image library, coupled with otolith-length and width to fish-length relationships, can be used for prey identification and back-calculation of fish size, making it a valuable tool for studies relating to food webs in the important yet poorly understood mesopelagic zone. In addition, the 44 fish barcodes generated in this study highlight the benefit of using an integrative taxonomic approach to studies of this nature, as well as add to existing public databases that enable cryptic species and metabarcoding analyses of mesopelagic species.
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This content will become publicly available on July 15, 2026
Osmoregulation by the gastro-intestinal tract of marine fish at depth – implications for the global carbon cycle
ABSTRACT Marine fish are likely one of the top producers of biogenic carbonate in the oceans. However, nothing is known about the production rate and composition of intestinal carbonate (ichthyocarbonate) excreted by mesopelagic fishes, which are small, fragile and account for up to 94% of global fish biomass. To address this knowledge gap, and associated uncertainty of global ichthyocarbonate production, we identified a model species residing at 350–430 m, depths relevant for mesopelagic fishes. The blackbelly rosefish (Helicolenus dactylopterus) lacks swim bladders and survives capture and transfer to the lab. Freshly collected blackbelly rosefish, maintained at 6°C, contained high amounts of intestinal ichthyocarbonate (0.4 g kg−1) and excreted ∼5 mg kg−1 h−1 ichthyocarbonate, in agreement with expectations based on allometric and thermal relationships for other species. Despite longer intestinal residence time, intestinal and excreted ichthyocarbonates are similar in crystallite morphology, composition and sinking rate, but have a higher dissolution rate than that produced by shallow water species at higher temperatures, ruling out strong effects of pressure and low temperatures on ichthyocarbonate formation and excretion. Considering allometric and thermal relationships, the metabolic rate of blackbelly rosefish is lower than that of other marine fish in general, and mesopelagic fishes in particular. Our observations support assumptions of ichthyocarbonate excretion by mesopelagic fishes, and suggest that thermal and allometric relationships for ichthyocarbonate excretion determined from shallow water species extend to fish populations at depth.
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- PAR ID:
- 10617285
- Publisher / Repository:
- The Company of Biologists
- Date Published:
- Journal Name:
- Journal of Experimental Biology
- Volume:
- 228
- Issue:
- 14
- ISSN:
- 0022-0949
- Page Range / eLocation ID:
- 1-14
- Subject(s) / Keyword(s):
- Blackbelly rosefish, mesopelagic fish, ichthyocarbonate, osmoregulation, intestinal fluid chemistry
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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