Managing fish farm from best species, feeding and overstocking

A fish from the university of Eldoret fishpond in Eldoret Uasin Gishu County. University of Eldoret (UOE) is currently at the forefront in conducting sex reversals on 20,000 fish and has a projection of 500,000 fingerlings. (PHOTO: ELIUD KIPSANG/ STANDARD)

Fish has a long history as a delicacy to man. In the Bible there are many stories revolving around fish. Jesus recruited his first batch of disciples in the Sea of Galilee as they were struggling to catch some fish. He would later feed 5,000 men and many women and children on a loaf of bread and five fish. After his death He appears to some of his disciples and they break a piece of roasted fish together.

The fish continues to make more stories today; his Excellency President Uhuru Kenyatta back in the days when he was Finance Minister saw fish as a potential economic stimulus activity; a venture that saw many fish ponds dug out throughout the country.

Right species

Masses were educated on fish keeping and societies that traditionally didn’t eat fish literally fought for more upon tasting the delicacy. Fish farming is therefore a relatively common venture in Kenya.

Today, I will shed light on fish farming ideas that a farmer can exploit to not only have enough fish to feed their family on but also for the market. First step is to select your species well. Selection of the species to keep should be influenced by the market demands and the type of fish pond you plan to establish.

Nile tilapia is a species generally accepted by the market and therefore has a higher demand compared to other scary species like barracuda.

Tilapia has the other advantage of being relatively tolerant to low oxygen and can survive in static ponds as compared to trout which require a lot of oxygen and will therefore do well in flowing waters thus requiring the presence of streams or lakes as water sources. For this reason tilapia and catfish are common on small scale ponds.

Stocking rates and fish sexes
Further to species selection, fishpond stocking has a great influence on the size of fish at maturity. Understocking will result in large but poor harvests which may not be economical.

On the other hand, overstocking will result in stunted growth and thus many but smaller fish at the end. You need optimal stocking rate which depends on the species kept and the weight at stocking. Tilapia should be stocked at two fingerlings per metre square.

Overstocking

Nile tilapia even when stocked at the correct rate will quickly mature within three months hence causing overstocking. There are two ways of dealing with the problem of overstocking in tilapia stocked fishponds either by keeping mono sex batches or by keeping mixed batches with catfish. You will need to have 100 catfish fingerlings for every 1,000 tilapia fingerlings. The catfish will feed on young tilapia effectively keeping them under a form of population control.

Mono-sex ponds

The other option of controlling the rapid breeding of tilapia is to either keep only female or male species in a pond to avoid breeding. Male tilapia is preferred for mono sex cultures because they grow rapidly and have more weight at maturity as compared to females.

Sexing (sex determination) can be done physically by checking the genitalia of the fingerlings. The sex of 20 grams tilapia fingerling can be determined by looking at the genital prominence (papilla) located just behind the anus. In males the genital papilla is more pronounced and has only one opening. Mono sex cultures can also be attained sex reversal which involves the treatment administration of male steroid to recently hatched fingerlings so that the undifferentiated genital tissue of generic female develops testicular tissue, thus functioning reproductively as males.

However, this technique has recently raised food safety and environmental issues associated with the use of steroids.

Fertilise your pond

Ponds should be fertile to support the growth of pond organisms which fish feed on. This is normally done by applying agricultural lime and organic manure into the pond. Organic manure can be got from rabbit, poultry, goat, sheep, cattle or donkey manure.

Lime has the effect of lowering the acidity of fish ponds. Pond acidity is due to carbon dioxide, a by-product of respiration of plants and animals and water pollution reduces that pH which makes it not conducive for the growth of phytoplankton. Lime increases the availability of nutrients, primarily phosphorous, to aquatic plants, specifically phytoplankton which is the fish’sstaple food.
Fish ponds can be continually fertilised by integrating fish farming with other enterprises on the farm; so that the byproducts or wastes are used as fish feed. For example you can build your poultry or rabbit house on top of a fishpond. When you are feeding the rabbits and poultry; feed that spills or the droppings will be consumed by the fish as they also fertilise the pond. This will reduce your operating costs by using the same labour force to do many tasks and will subsequently increase your profits.

When to feed your fish

In as much as your fish will get its feed from the pond; it will quicken their growth rate if this is supplemented. Tilapia will typically feed throughout the day to meet their daily body nutrient needs as they have a smaller stomach. The best time to do your supplemental feeding is between 10 o’clock in the morning and 4 o’clock in the evening when water temperatures and dissolved oxygen are relatively high. Even when given feeds; fish are selective and will only feed on what they need at a time (they don’t overfeed). Unlike in cattle or dogs where you placefeed in some apparatus in fish ponds this feed is broadcast on water and when it is not consumed by fish another hazard will be created. The excess feed will stay in the pond water, will be broken down and will change the colour and taste of the water and will thus require extra manpower to clean.
To avoid this, assign some quality time to feed the fish; throw in the supplemental feeds in small portions at specific sites and observe how they eat. Normally when hungry they will come to the surface immediately they see the feed. When diseased; lack of appetite is one of the clinical signs observed and there is no other best time to pick this other than at feeding time.

(The writer is a veterinary surgeon working with the Kenya Tsetse and Trypanasomiasis Eradication Council - KENTTEC)