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Water temperature, the triggering factor
Black bass reach sexual maturity at the age of 2 or 3, at a size of 25 to 35cm. At the end of winter, they emerge from a lethargic phase to feed in preparation for reproduction. The first signs of spawning occur when the water reaches 15 to 16°C, peaking at 18°C.
So, depending on the region and the configuration of the body of water in question, breeding can start as early as around March 25 for the earliest ponds, whereas in rivers it can only start in mid-May, for example.
Generally speaking, in France, reproduction peaks in May, and can be considered to extend from early April to late June in lakes, and from early May to mid-July in rivers. What's more, contrary to popular belief, not all fish reach the spawning grounds at the same time. Some fish are later than others, and females will often divide their spawning among several nests.
The influence of the moon plays an important role in this spread, as full moons tend to trigger a wave of reproduction.
The reproduction process
When the water reaches 15-16°C, the fish will gather and a few males will dig the first nests on well-exposed banks that gain a few extra degrees. Nests are dug in a medium to fine substrate, such as gravel, or on a fine fibrous support. In the absence of a gravelly substrate, they can find another support, notably stumps, which are very popular in muddy environments (or judiciously installed artificial spawning grounds!).
Once the nest has been cleaned, the male will begin to protect it and stand over it, waiting for a female to come along. The latter will only lay eggs if her oocytes are mature. So some males have to be patient before a lady comes... When the female is ready, she approaches the nest and the male pushes her towards it. This is the beginning of a rather delicate courtship. The male becomes increasingly aggressive, even biting the female, kicking her in the stomach and head, to "force" her to expel her oocytes.
Once the female is ready, she deposits her oocytes, which are rapidly fertilized by the male. The act may last several hours, and the female may remain close to the nest for several days, returning to deposit oocytes. The nest will thus receive 5,000 to 12,000 eggs from one or sometimes several females.
Just after fertilization, the male ventilates the eggs that have adhered to the substrate. This is also the time when he will intensify his guarding of the nest. Many predators want to gorge themselves on the eggs: bream and other whitefish, sun-perch, pseudorasboras, crayfish, etc. The male will spend seven to fourteen days guarding the nest. The male will spend 7 to 14 days without feeding, protecting the nest while the eggs incubate, hatch and the fry finish absorbing their yolk sac.
Once the fry have reached the "free-swimming" stage (i.e. after resorption of the yolk), the male will keep them in a ball. At first, he will keep them close to the nest, then follow their movements while keeping a watchful eye on them, as there are many predators out there. Occasionally, males will group together their fry balls and work together to protect all these little creatures! During this period, in addition to predation, the survival of the fry is also highly dependent on food resources.
At first, larvae feed on protozoa such as rotifers and copepod nauplii, smaller than 150µm. Then, at the fry stage (when they become pigmented), they feed mainly on zooplankton (copepods, cladocerans, etc.), followed by invertebrates, insect larvae and fish as they grow.
Finally, when they reach 2 to 3cm in length, the male will end his supervision and leave the fry to fend for themselves. Depending on the water temperature, he will have spent 3 to 5 weeks entirely devoted to his offspring, and as a result emerges from the reproduction process lean, weak and damaged. The weeks that follow are therefore entirely devoted to feeding, to restore their health!
