The development of techniques to induce spawning or reproduction in fish is one of the most significant advancements in the field of aquaculture during recent decades. These techniques have allowed farmers to profitably breed and raise fish species that do not naturally reproduce in captivity (or in a pond), and to manipulate the timing of reproduction to suit production cycles.
The reason some species will not readily breed in captivity is because of environmental or culture conditions that are different from those found in nature (or rivers and oceans). This change is conditions of water temperature or substrate type may cause stress for the fish or may not provide the cues needed for them to complete the reproductive process.
Why Induce Spawning
Because fish in ponds may not not naturally reproduce at the most advantegous time, it becomes important and advantegous to alter the spawning cycle. This allows a farmer to:
- improve efficiency by getting fish to spawn on a predetermined date.
- obtain fish outside of the normal spawning season; and
- maximize survival by fertilizing and incubating eggs under hatchery conditions.
The Reproductive Nature in Fish
In fish, the reproductive process involves three basic steps:
- maturation – the development of the gametes (eggs and sperm) to a point where fertilization can occur;
- ovulation – the release of eggs from the ovary; and
- spawning – the deposition of eggs and sperm so that they can unite.
How to Induce Spawning
There are two main strategies used to induce reproduction in fish.
- Provide an environment in which spawning occurs naturally.
The first step is to create a natural environment, like rivers and seas, where spawning can naturally occur.
Since catfish, for example, like to spawn in enclosed spaces such as hollow logs, a farmer can simulate this by putting milk cans in a pond. - Inject the fish with natural or synthetic spawning hormones
This is only effective in fish that are already in breeding condition and have mature eggs in which the germinal vesicle has migrated. Often the two strategies are used sequentially: the first to manipulate maturation, then the second to induce ovulation.
Though numerous hormones have been used to induce reproduction, the injection of gonadotropin has emerged over the past few years and seem to offer the best chance for success at the least expense.
Fish Spawning Hormone
Check out these fish spawning hormone products that contain gonadotropin. We have ovaprim, ovulin and ovapec.
Methods of Inducing Spawning
The details of inducing spawning differ from species to species. However, the process is the same.
Preparing The Broodstock
Brooders should be disease free and sexually mature. These are several indicators of sexual maturity:
For Females
- The abdomen is rounded and soft.
- The genital opening is swollen, protruding, and reddish.
- The anus is often also swollen and reddish.
For Males
- Milt is released when the abdomen is pressed gently.
- Secondary sexual characteristics are evident.
Brooders must be handled with extreme gentleness because they are physically very vulnerable during spawning and may die if dropped or roughly handled. Don’t’ let all the potential return from developing the broodstock line and keeping the fish healthy be easily eliminated through sloppy handling.
When the brooders are kept in ponds or pens, all water quality parameters, such as temperature and oxygen, should be kept at optimal levels. A satisfactory amount of high quality, well-balanced feed should be provided.
Check out our water test kits and quality fish feed.
If the fish are moved from one set of conditions to another, time must be allowed for acclimation. When handling the fish, gentle firmness should be the rule. Covering the fish with wet burlap or cloth, or covering their container to cut off light, will help to keep them calm. Tranquilizers may be used when fish are to be injected or stripped.
Injecting the Fish – Video
This is for carp and catfish.
Extracting the Sperm and Eggs
After injecting the fish hormone into the female broodstock, you wait for some hours for the eggs to multiply and then gently press the fish abdomen to get the spawned eggs into a clean bowl. You will also need to extract the sperm from the male broodstock and add it to the eggs. See more in the video below.
Conclusions
Many species of fish will not readily reproduce under pond conditions. Others will, but not necessarily when the farmer desires. In both cases, to induce spawning is more advantegous.
These two techniques of induction are commonly used, sometimes sequentially. The first is the manipulation of the pond environment to mimic some important quality in the fish’s natural environment. The second is the injection of hormones to stimulate spawning. The hormones may be natural hormones taken from fish or other animals, genetically engineered from bacteria, or synthetic analogs of naturally-occurring hormones.
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