Golden Dorado
Spawning Season
I have been extremely fortunate over the past twenty-five years, to travel at least once every season to the northern corners of Argentina and the bordering countries in search of Golden Dorado. My journeys have taken me to some of the most beautiful and diverse environments imaginable.
I’ve enjoyed watching these incredible fish as they live, feed, and survive, in various types of fisheries and waterways. But only a few times in all of these years, and only in the farthest reaches of the Upper Parana River, was I lucky enough to witness the unparalleled drama of the Dorado spawning.
A Great Dorado Migration
Every season, Golden Dorado migrate between 400 to 700 miles north to reach their spawning grounds in the Upper Parana. The migration also takes place at a time when the river is perfect for other species of river fish to reproduce, and they all share the same waters.
Typically, in a window of time between late October and January, river conditions will trigger the event. Dorado who are residents of the upper waters, many of which are massive fish, will mix with those who made the long migration to begin the incredible display. It’s something everyone should witness someday.
The first indicator of the coming Golden Dorado spawn, will be the sudden migration of the Sabalo (the main food source of the Dorado.) When you see the first enormous schools, as in millions of fish moving simultaneously, that’s the first indication the migration has begun. Within twenty-four to forty-eight hours, and always corresponding with the highest temperatures, it’s possible to see Sabalos and Golden Dorado joining each other in the middle of the river for the spawning run.
Uniquely - Dorado Spawning
Unlike trout and other Salmonid species, which seek out specific bottom conditions to make a bed, Golden Dorado spawn in the upper column of water in the center of the river. The other difference is that Dorado don’t unite in typical male-female couples to lay and fertilize eggs. Female Dorado, closely followed by several males, will cast their eggs into the current where the males will collectively fertilize them as they pass.
Golden Dorado exhibit extreme sexual dimorphism, where males grow to an average weight of only twenty pounds, and females typically reaching 40, with a few exceptional ones in the 60 pound range.
The spawning location is carefully chosen, water with enough velocity and turbulence in the current to increase the probability that eggs will be introduced to the sperm of several different males. If the water is too slow, the eggs will sink to the bottom unfertilized and perish.
The Natural Beauty of Floods
The natural cycles of flooding in the upper river system are also essential for the survival of the Dorado. Seasonal floods that raise the river’s water level far above normal, will fill the floodplains, wetlands, backchannels, and lagoons, connecting them once again with the river. That connection brings new flowing clear water, nutrients and food, and creates the perfect “nursery” conditions to support the juvenile Dorado. These young Dorado will remain in the nursery between 6 months up to 2 years or more, depending on the flood cycles. When they are big enough, and the floods once again provide a connection of flowing water, they will move to the main river for the first time in their lives.
It is believed the eggs, once fertilized, might travel between 10 to 35 miles in the river current before hatching, which can happen in as little as 13 to 19 hours depending on the water temperature. This extreme distance usually results in the young Dorado being hatched within the safety of the nursing areas, in the flooded backwaters and wetlands, where the newly born are able to feed and grow with little threat of predation.
From Small to Legendary Giants
The infant Dorado are born with an egg yolk sack that only lasts about a day after hatching. They must begin feeding themselves almost immediately, which is likely why they are born with such extraordinary predatory instincts. From the first moment, they will choose food as large as they can find, with the only limit being the size of their mouth! In the earliest days, being between 2 to 6 inches in length, they feed mostly on small insect larvae and quickly increasing to adult and larger insects. As they approach 6 inches in size, they will also start to add small fish to their diet, and above 8 inches they eat almost exclusively other fish, with Sabalo becoming their main meal.
The spawning process of the Golden Dorado is unique, and intricately woven within the matrix of a complex river ecosystem. And while very limited scientific research has been done to understand it in detail, we have enough knowledge to realize how hard it would be to recreate the natural conditions necessary to artificially reproduce the species. Further research is needed to understand them, and to protect this amazing game fish.
Fortunately, every year in spring and early summer, when the rivers swell and the rich floods fill the plains and wetlands, the Golden Dorado population goes through an exponential recovery all on its own. So for the time being, our job is to simply drive forward the conservation efforts to keep the rivers flowing the way nature intended.