Metopa sp.
  Metopa sp. (Family Stenothoidae)


Welcome to the Stomach Examiner's Tool (SET). Here, we present information that is useful when performing stomach content analysis of marine fish collected in Alaskan waters; the eastern Bering Sea, Gulf of Alaska, and Aleutian Islands. The information provided here should also be helpful for analysts working on the food habits of marine fish in the coastal waters of Washington, Oregon, and California.

The Food Habits Laboratory of the Alaska Fisheries Science Center (AFSC) Resource Ecology Ecosystem Modeling Program (REEM) has been collecting data on the food habits of commercially and non-commercially important fish species since the early 1980s. Over the 30+ years of processing stomach contents, we have accumulated a wealth of taxonomic information that is useful for identifying prey found in marine fish stomachs. We have used a digital camera to record the distinguishing taxonomic features of whole specimens, partially digested specimens, gill arches, vertebrae, postcleithrum, otoliths, telson of crustaceans, subopercle and preopercle of fish, setae of polychaetes, and other slow digesting hard parts. The objective of this web site is to provide the comprehensive information as a guide for stomach content analysts to identify the prey items in marine fish stomachs quickly and easily. Prey images and data presented here include pelagic (water column) prey such as zooplankton, small forage fish, juvenile and adult groundfish and benthic prey (on the sea floor) prey such as shrimp, crab, juvenile and adult groundfish, marine worm, amphipods, clams and snails.


The Resource Ecology and Ecosystem Modeling (REEM) program at the Alaska Fisheries Science Center has been collecting and processing stomachs of the marine fish collected from the eastern Bering Sea (EBS), Gulf of Alaska (GOA), and Aleutian Islands (AI) since 1983.

Diet data are used to describe feeding ecology and predator-prey relationships and are used for mortality estimation, fishery management and ecosystem modeling. Therefore, many researchers encounter situations where they need to get diet data by processing fish stomachs.

During the past 30 years, many people have contributed to the collection of useful taxonomic information (e.g., vertebrae, gill arches, otoliths of fish; pictures of partially digested fish and invertebrates) for the identification of prey of the marine fish.

This web-based, Stomach Examiner's Tool (SET) provides comprehensive information as a guide for the stomach content examiner to identify the prey items in the stomachs of the marine fish in the Alaska waters. This online service will guide you to find the possible prey of a specific predator, help you to distinguish the similar taxonomic species or groups, and how to narrow down the scope of your unknown prey items. These data will be updated routinely, when new information or new tools for the improvement of prey identification are added.



The Trophic Interaction Program (Food Habits Lab) in the Resource Ecology and Fishery Management (REFM) Division of the Northwest and Alaska Fisheries Center (NWAFC) was created in 1983. Initially the program systematically collected fish stomach samples annually from the eastern Bering Sea, however stomach sampling was extended to the Gulf of Alaska and Aleutian Islands in 1990 and 1991, respectively. The NWAFC was split into Alaska Fisheries Science Center (AFSC) and Northwest Fisheries Science Center (NWFSC) in the late 1980s. The Trophic Interaction Program was subsequently renamed to Resource Ecology and Ecosystem Modeling (REEM) program as part of AFSC.

Stomach samples of commercially important predator species, such as walleye pollock (Gadus chalcogrammus), Pacific cod (Gadus macrocephalus), Pacific halibut (Hippoglossus stenolepis), arrowtooth flounder (Atheresthes stomias), Kamchatka flounder (Atheresthes evermanni), Greenland turbot (Reinhardtius hippoglossoides) yellowfin sole (Pleuronectes asper), rock sole (Pleuronectes bilineatus), flathead sole (Hippoglossoids elassodon), and Alaska plaice (Pleuronectes quadrituberculatus), were the primary focus when the program began. However, sample collections were expanded to ecologically important, non-commercial species, such as skates, osmerids, myctophids, bathylagids, rockfish, cottoids, zoarcids, and many others in the later years.

Generally, taxonomic guides use external physical characteristics to identify organisms. However, due to the varying degree of the digestion seen in consumed prey items (from no digestion to partially digested, to highly digested), we have had to develop alternative methods of prey identification. We primarily depend on digestion resistant hard parts such as boney structures (e.g. vertebrae, gill arches, subopercles, post cleithrum, otoliths), setae, jaws, and ossicles that remain in the stomachs to identify the original prey. Over the past many years, we have collected both specimens and photos of these diagnostic prey parts to help identify prey commonly found in North Pacific predators.

Our collection includes images of taxonomic characteristics relevant to the identification of whole specimens, partially digested specimens, gill arches, vertebrae, postcleithrum, otoliths, telson of crustaceans, subopercle and preopercle of fish, and setae of polychaetes, etc. By making this information available online, our colleagues, students, and anyone is interested in stomach content analysis can quickly and easily access it.


Stomach Content Collection and Analysis Manual

The Lab Manual (.pdf, 122KB) describes details of the stomach content analysis procedures used by the Resource Ecology and Ecosystem Modeling program in Alaska Fisheries Science Center. It covers sample preparation, recording predator and prey data, quantitative stomach analysis, qualitative stomach analysis, prey size data, and some special techniques used to identify prey.

Manuals describing at-sea fish stomach collection techniques, sample design and stratification are available on the REEM Manual page


Prey Identification

There are many references to help with the identification of different prey from a variety of fish stomachs. Some important characteristics for distinguishing similar prey items (e.g. juvenile walleye pollock and capelin) are included in the comments of the specific prey species in the main categories (e.g. gill arch, vertebral column).



We thank many people who have been involved in this project over the past 30 years. In the early days, Frank Morado and his Pathobiology lab let us use their digital camera equipment for gill arch pictures, we thank them. Karna McKinney, with her expertise in photography, gave us lessons and showed us the basics of using Photoshop. Without her help, we would not be able to have this accomplishment. Most of the Photoshop work was done by Kim Sawyer and Mei-Sun Yang.

The Lab Manual (.pdf, 122KB) was most recently contributed to by Troy Buckley, Geoff Lang, Mei-Sun Yang, Rick Hibpshman, Caroline Robinson, Kim Sawyer, and Sean Rohan.

Jeff Cordell, at the University of Washington, has been identifying some specimens for our lab and giving his taxonomic expertise during the past many years. Morgan Busby, Ann Matarese, and Debbie Blood (FOCI) have been identifying fish larvae and eggs for us. We appreciate their constant help.

Geoff Lang is our data manager, he developed the data base and created this web page for us. This 2021 update to this site was completed by Steven Wang.