The eel is a long, thin bony fish of the order Anguilliformes. Because fishermen never caught anything they recognised as young eels, the life cycle of the eel was a mystery for a very long period of scientific history. Although more than publications mention eels, much of their life history remains an enigma. The European eel Anguilla anguilla was historically the one most familiar to Western scientists, beginning with Aristotle , who wrote the earliest known inquiry into the natural history of eels. He speculated that they were born of "earth worms", which he believed were formed of mud, growing from the "guts of wet soil" rather than through sexual reproduction. Many centuries passed before scientists were able to demonstrate that such spontaneous generation does not occur in nature.
Eels Don’t Have Sex Until the Last Year of Their Life - Issue Love & Sex - Nautilus
Catadromous eels enter fresh water as sexually undifferentiated glass eels and develop into males and females before migrating back to sea as silver eels. Females develop ovaries directly from the ambiguous primordial gonad whereas males pass through a transitional intersexual stage before developing testes. Eels have sex-specific life-history strategies. Males may grow faster than females initially, but this difference is soon reversed and females attain a greater age- and size-at-metamorphosis than males. Male fitness is maximized by maturing at the smallest size that allows a successful spawning migration a time-minimizing strategy whereas females adopt a more flexible size-maximizing strategy that trades off pre-reproductive mortality against fecundity. Although heteromorphic sex chromosomes have been identified in some species, the sex of developing gonads is labile and gender is determined principally by environmental factors.
Eels Don’t Have Sex Until the Last Year of Their Life
In March , the young Sigmund Freud arrived in Trieste, looking for the testicles of an eel. For centuries past, these troublesome organs had proved elusive. Despite the most intensive — not to say intimate — research, no one had managed to track them down. Recently, however, a Polish scientist, Simone de Syrski, claimed to have solved the puzzle and Freud, then a promising medical student at the University of Vienna, was despatched to see if he was right.
Environmental sex determination ESD has been detected in a range of vertebrate reptile and fish species. Because several eel species are at risk of extinction, assessing sex at the earliest stage is a crucial management issue. Based on preliminary results of RNA sequencing, we targeted genes susceptible to be differentially expressed between ovaries and testis at different stages of development. Using qPCR, we detected testis-specific expressions of dmrt1 , amh , gsdf and pre - miR and ovary-specific expressions were obtained for zar1 , zp3 and foxn5. We showed that gene expressions in the gonad of intersexual eels were quite similar to those of males, supporting the idea that intersexual eels represent a transitional stage towards testicular differentiation.