# Codfishes Compensated for Essential Gene Loss via Aqp4 Channel Adaptation

- Published: 2026-11-06 15:45 UTC
- Section: Life & Health › Biology & biochemistry
- Tags: codfishes gene loss, Aqp4 water channel, pelagic egg hydration, Gadiformes evolution, oocyte hydration mechanism
- URL: https://realtech.media/news/rt-d4546e01d71de005f8c0b204_codfishes_compensated_for/

**Biologists found that codfishes produce buoyant pelagic eggs despite losing the aqp1ab genes by co-opting the Aqp4 water channel.**

![Codfishes Compensated for Essential Gene Loss via Aqp4 Channel Adaptation](https://sgzwpqqelzmajkcubgkl.supabase.co/storage/v1/object/public/rt-media/2026/11/a1b3e0130e5abf3a.webp)
*scinexx*

Biologists led by researchers from the University of Bergen revealed how codfishes generate highly hydrated floating eggs despite lacking genes long considered vital for embryonic survival, according to a study published in the Proceedings of the National Academy of Sciences [1]. All members of the order Gadiformes completely lost the aqp1ab-type aquaporin genes that typical marine teleosts rely on to hydrate their pelagic eggs [1]. Despite this genetic loss, Atlantic cod produce pelagic eggs with water contents ranging between 93 and 97 percent [1].

Comparative transcript analyses across freshwater and marine teleosts showed that the osmotic drive mechanisms driving water uptake remain preserved in cod [1]. Proteolysis of yolk proteins into free amino acids continues to build the necessary osmotic gradient [1]. However, instead of utilizing the lost channels, Gadiformes co-opted an Aqp4-type channel that has been chromosomally linked to the Aqp1-type channels in jawed vertebrates for over 450 million years [1].

## Co-opting Freshwater Pathways

Functional assays, immunolocalization, and inhibition experiments performed on Atlantic cod and zebrafish demonstrated distinct physiological roles for the short isoforms of Aqp4 [1]. In zebrafish, representing ancestral freshwater lineages, Aqp4 is strictly required during ovulation for follicular egg release [1]. Targeted inhibition experiments in Atlantic cod confirmed that blocking Aqp4 directly prevents the massive hydration of the maturing oocyte rather than ovulation alone [1].

## Evolutionary Transition

Comparative genomic data from closely related taxa indicate that the loss of aqp1ab and the subsequent recruitment of Aqp4 occurred between 60 and 84 million years ago [1]. While ancestral and modern pelagic marine lineages continue to depend on aqp1ab, Gadiformes averted reproductive failure by repurposing the existing freshwater ovulatory machinery [1].

## Sources

1. [Proceedings of the National Academy of Sciences](https://doi.org/10.1073/pnas.2626713123)
2. [scinexx](https://www.scinexx.de/news/biowissen/dorsche-kompensierten-den-verlust-lebenswichtiger-gene)

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Source: RealTech, realtech.media — https://realtech.media/news/rt-d4546e01d71de005f8c0b204_codfishes_compensated_for/