The development of eggs in fish: reproductive processes, types and strategies
The fish They stand out for their reproductive diversity, adaptability and variability of strategies to perpetuate the species in aquatic environments. Understanding the formation, development and characteristics of the eggs de peces It is key not only for marine biology, but also for aquarium hobby, conservation and aquaculture.
Characteristics and structures of eggs de peces
The eggs of bony fish are generally transparent and round in shape. They have a permeable outer membrane with pores, called chorionIn most species, this membrane is smooth, although some exhibit a hexagonal lattice or other ornamentation useful for identification. Egg size varies considerably depending on the species, generally between 0,25 and 7 mm in diameter, with the average being close to 1 mm. Optimal egg size maximizes both the number of eggs and the future survival of larvae and juveniles.
Inside the eggs is the yolk, whose function is to store the necessary energy reserves and nutrients for the embryo to develop until it can feed itself. In some cases, the yolk occupies almost the entire egg, leaving only a peripheral margin free.
Types of eggs according to habitat and reproductive strategy
- Benthic eggsLarger, with abundant yolk and fewer in number, they are deposited on the bottom and attached to substrates or protected by nests. They usually have a longer embryonic development. The larvae emerge in a more advanced state, with already differentiated sensory structures.
- Pelagic eggs: Smaller and more numerous, they float freely in the water column, with less yolk and less protection, which implies greater vulnerability but greater fertility. The relationship between the egg size and larval survival is important: large larvae can consume a variety of prey and evade predators better.
Some species present a remarkable ovoviviparity o viviparity, where fertilization is internal. Here, the female houses the eggs inside her; in viviparous animals, the young receive maternal nutrients, while in ovoviviparous animals, they use the yolk of the egg. Some sharks, rays, and freshwater fish display these reproductive types.
Reproductive behaviors and protection of offspring
- Some species make nests based on bubbles, vegetation or in the substrate, where they lay their eggs and actively protect them, oxygenating the water and defending the spawn.
- In certain fish, such as seahorses and cardinalfish, the males incubate the eggs in their nests. incubator bags or in the mouth.
- There are species that carry their eggs in their gill chambers or other body structures.
- In others, especially pelagic species, there is no parental care; survival depends on the number of eggs and dispersal.
Hermaphroditism and evolutionary strategies
Many species present sequential hermaphroditism, changing sex during their life cycle (proterogyny: female to male, as in parrotfish and wrasses; protandry: male to female, as in clownfish and sea breams). In rare cases, simultaneous hermaphroditism, both sexes being able to act at the same time, as in some serranids. There are complex courtship behaviors, reproductive migrations (anadromous and catadromous) and, exceptionally, asexual reproduction in some species such as the Amazon molly fish (Poecilia formosa).
Incubation and embryonic development
El embryonic development It begins with fertilization and involves several phases: water absorption (swelling), cell segmentation, formation of the blastoderm, and development of the embryo around the yolk. Environmental factors, especially the temperature and the oxygen, have a decisive influence on the duration and success of development. When the larvae emerge, they use the remaining yolk before beginning to feed on the environment, which marks the beginning of the fry stage.
The study and knowledge Detailed examination of fish eggs and early life stages is essential for the conservation and sustainable management of aquatic populations, as well as for species identification and the planning of protected areas. These processes reflect the extraordinary biological and adaptive diversity that characterizes fish and their environments.
