Environment Dependent Dietary Adjustment by Invasive Aquatic Species

Fatin Chowdhury ‘20

Figure 1. Knodus moenkhausii is a fish species that invades Brazil’s, including its Paranai´ba River. In the detailed research article, researchers explain how the fish’s diet and related environmental conditions were investigated.

Recently, researchers at three Brazilian universities examined patterns of feeding behavior displayed by the Knodus moenkhausii fish invasive to Brazil. The researchers described a two-fold hypothesis. Firstly, the species is expected to be non-specialist and opportunistic, feeding on whatever food source is most readily accessible. Secondly, resource abundance affects the nature of the trophic niche it resides in. Accordingly, flexibility in diet and occupied trophic niche were observed as according to differing environmental conditions. 

Specimen samples were collected from six streams located in the Paranaı´ba River’s sub-basin. Three of the streams were positioned in locations that were predominantly used for pasture, while the other three streams were adjoined by river water influencing vegetation. The percentage cover of pasture and vegetation was determined via satellite imagery. Stereomicroscope facilitated stomach content data was collected in order to discern how selective the species were when feeding, while 2 to 5 grams of entire-specimen carbon and nitrogen based isotopic data, analyzed via mass spectrometry, were used to pinpoint relevant trophic levels. Food resource specimens were collected, including organic matter and benthic macroinvertebrates. Diet patterns were detailed in part by utilizing a feeding index equation which incorporated frequency of a food’s appearance in samples, and other factors. 

The researchers employed linear regression when analyzing stomach content data, while the isotopic data of fish from pasture and natural cover proximate areas of river were examined via generalized linear mixed models. Trophic position of the fish was found via a calculation based model, while t-test based statistical analysis was used to analyze whether there was a significant difference in trophic level according to river area. The data confirmed K. moenkhausii as an omnivorous species. Pasture adjacent stream data indicated that macroinvertebrates consumed by the fish were found in stomach at levels proportional to their natural distribution. The researchers found that the fish’s diet was dominated by non-predator macroinvertebrates in streams near abundant natural cover. The researchers asserted that these findings indicate how a species, in response to changing aspects of a habitat, can be flexible in exploiting environmental resources and adjusting their trophic niche occupation.



  1. de Carvalho, et al., Stable isotopes and stomach content analyses indicate omnivorous habits and opportunistic feeding behavior of an invasive fish. Aquatic Ecology 53, 365–381 (2019). doi: 10.1007/s10452-019-09695-3.
  2. Image retrieved from: https://unsplash.com/photos/IfsvDZBSeWc

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