Growth Phases 101

Tilapia growth can generally be broken into three distinct phases:

• Exponential or Accelerating Phase
• Linear Phase
• Decelerating or Plateau Phase

Young fry are ravenous eaters and they can consume feed that is equivalent to up to 25% of their body weight daily. As a result, the fish grow very fast when measured in percent of body weight per day. This phase is referred to as the Exponential or Accelerating Phase. However, since the fish are initially very small, the total weight gain is initially low. This rate of weight gain (in grams per day) increases until the fish weigh approximately 100 grams, at which point they enter the Linear Phase of growth.

During the Linear Phase, Tilapia eat approximately the same amount each day and the growth remains fairly linear. Their feeding rate does not change drastically during this period because, although the fish are growing, they eat less feed as a percent of their body weight as they grow. The duration of the linear growth phase differs dramatically with the species and strain of tilapia. Some inferior strains may show growth deceleration at sizes of less than one pound.

When fish growth begins to decelerate, they enter what is referred to at the Plateau Phase. At this point, it begins to take more food and time to achieve a given amount of growth. This can be very frustrating for the aquaculturist who is trying to get fish to market. Cheaper fingerlings often become more expensive in the long run due to poor genetics.

During an in-house growth trial of AmeriCulture Tilapia, the linear growth phase of genetic males was maintained up to a size of approximately 3 pounds before decelerating. This is an important consideration for aquaculturists who want to get their fish to market size before they begin to plateau. Of course, the fish must be reared optimally from the time they arrive at your facility in order to achieve these types of results

For practical reasons, the rearing of tilapia is generally divided into three distinct segments:

• Hatchery Phase
• Nursery Phase
• Growout Phase

The Hatchery Phase component is what we do at AmeriCulture. We breed the parental broodstock and rear the fingerlings to an average size of 0.4-0.5 grams. During this phase, we use a conventional sex-reversal technique to produce predominantly male tilapia fingerlings. The hatchery phase is best left to a professional hatchery that is able to allocate the time, space, and resources necessary to a genetic development program so that you can keep pace with the growth, color, and conformational requirements of the industry. Additionally, growers can often buy higher quality fingerlings from a professional hatchery for less money than they could ever produce them for.

The next phase is generally referred to as the Nursery phase. During the nursery phase, small fingerlings (commonly referred to as "phase 1 fingerlings") are reared to a larger size, typically ranging from 20 to 50 grams. These are called "stockers" or "phase 2 fingerlings". Fish of this size are more suitable for stocking into large production tanks. Because of transportation costs, stockers don't generally comprise a large proportion of the production of professional hatcheries-it is generally done at the production site. The nursery phase generally determines the variation in size that the farmer will have when the fish reach market size. If the farmer manages the nursery phase poorly, he will have a mess on his hands. If he manages the nursery phase wisely, he will have a much easier task on his hands when it comes to grading and harvesting the final product. We have customers who have had only 2% of their fish fall outside the range of 1.25 to 1.33 pounds at harvest time. This indicates superb husbandry during the nursery phase. Best results are achieved when the fish are not overcrowded, and are fed an appropriately-sized, high-protein diet, while maintaining excellent water quality.

The final phase is the Growout Phase. This is basically the "feed-lot" component of the aquaculture operation. It begins when the stockers are transferred from the nursery tanks to the growout tanks. Once the fish reach a size of approximately 100 grams, they eat and grow roughly the same amount daily. The goal is to push as much high quality diet through them in the shortest period of time in order to maximize profits.

The total time period to reach market size generally takes 7-8 months on average. Some have done it in less that six months, while others have taken a year. The difference between these extremes is simple; environment, husbandry, and disease. Superior, detail-oriented growers will always make more money in the end than will careless, inattentive growers. We hope this information will assist you in becoming one of the former. All the best!