Feeding studies take guts – critical review and recommendations of methods for stomach contents analysis in fish

Abstract

Studies on the feeding ecology of fish are essential for exploring and contrasting trophic interactions and population and community dynamics within and among aquatic ecosystems. In this respect, many different methods have been adopted for the analysis of fish stomach contents. No consensus has, however, been reached for a standardised methodology despite that for several decades there has been an ongoing debate about which methodical approaches that should be preferred. Here, we critically review and scrutinise methods, addressing their strengths and weaknesses and emphasising inherent problems and possible pitfalls in their use. Although our critical assessment reveals that no completely ideal approach exists, appropriate and reliable procedures can be adopted through careful considerations and implementation. In particular, we advocate that different objectives require different methodical approaches and the choice of method should therefore be closely linked to the research questions that are addressed. For a standardisation of methods, we recommend a combination of the relative-fullness and presence-absence methods as the optimal approach for the commonly applied feeding studies addressing relative dietary composition in terms of prey diversity and abundance. Additionally, we recommend the gravimetric method for objectives related to the quantification of food consumption rates and the numerical method for prey selection studies. DNA-based dietary analysis provides a new and promising complementary approach to visual examination of stomach contents, although some technical challenges still exist. The suggested method standardisation facilitates comparisons across species, ecosystems and time and will enhance the applicability and benefits of fish feeding studies in trophic ecology research.

A trophic latitudinal gradient revealed in anchovy and sardine from the Western Mediterranean Sea using a multi-proxy approach

“…Recently, DNA metabarcoding has emerged as a useful technique to study the trophic ecology of several organisms 22 – 24 . However, these techniques are not so often combined with other methods to enhance their utility.…”

“…In the absence of potential prey stable isotope signatures (imperative to estimate the assimilated diet), they still provide useful information about trophic position, isotopic width and overlap, as a proxy of trophic niche width and overlap between species 36 , 37 . Thus, the combination of different techniques can provide new insights and show a general overview of the feeding ecology of organisms 22 (Table 1 ).…”

Seasonal dietary shifts enhance parasite transmission to lake salmonids during ice cover

“…Only amphipods, insect larvae, zooplankton, and fish were considered for the stomach‐parasite analysis, as they are the potential intermediate hosts of the identified intestinal parasites. The importance of these prey in the fish was expressed as frequency of occurrence (Amundsen & Sánchez‐Hernández, 2019). The dietary information from the individual stomach samples was incomplete due to a high number of empty stomachs (Arctic charr N = 115, brown trout N = 29), especially during winter‐time.…”

Reciprocal Role of Salamanders in Aquatic Energy Flow Pathways

“…Smiroldo et al [80] revealed that the frequency of occurrence of amphibians in dietary studies in Eurasian otters averaged 12%. Considering that the frequency of occurrence only covers the total number of stomachs with prey and thus without taking the relative abundance of each prey type into account [119], it is doubtful that the use of literature sources only including frequency of occurrence can draw conclusions regarding the importance of salamanders as energy resources for otter species compared to papers reporting the abundance (numerical, biomass, or volume) of prey categories. Salamanders commonly represent a small portion of the stomach contents in brown trout and northern pike (Exos lucius) [54,77,78], which underscores the small importance of salamanders as energy subsides for piscivorous fish species such as, for example, many salmonid and pike species.…”