Overall comparisons of marine pelagic productions in different systems are speculative to a high degree. Yet they often bring to our attention processes which have not been sufficiently investigated. One such process may be the decrease of fish production due to the change in the diatom/flagellate ratio. The following hypothesis is discussed in the light of recent investigations: An increasing development of flagellates caused by some types of pollution or climatic changes not only may increase the number of trophic levels and thereby, decrease fish production, but also may cause a change in the flow of biomass from fish to ctenophores and other planktonic predators, thereby again decreasing the harvest available for human consumption.