Features Fish Nutrition Research
Focus on diet to improve performance indicators in African catfish (Clarias gariepinus) fingerlings and juveniles

Fast growth rate, threshold for extremely high stocking density, tolerance for the environment and a ready market are just some of the strengths of culturing African catfish (Clarias gariepinus). Fully tapping the market potential, however, is stymied at the grassroot level, including insufficient availability of fingerlings and mortality rates. Many researches focus on diet to improve performance indicators.

Dietary benfotiamine

In the Philippines, where survival rates in African catfish from fry to juvenile stages swing wildly between five and 80 per cent, there is a clamour for fry that deliver, at the very least, sound projections for the grow-out operation.

A “minute” application of benfotiamine, a synthetic pro-vitamin B1 and a lipid-soluble derivative of thiamine, to fry diet offers a solution.

The study by Rey Obeda et al., “Dietary benfotiamine in high carbohydrate diet improves growth and resistance to abrupt shift to higher salinity in the African catfish (Clarias gariepinus) juveniles”, demonstrated that supplementation of benfotiamine to the high carbohydrate (HC) fry diet at 0.02 per cent produced juveniles with enhanced performance parameters and higher survival rates. The authors are affiliated with the University of the Philippines – Miagao, Iloilo. 

The other diets in the study experiments contained 15 per cent cornstarch as a source of carbohydrate (control), and a high carbohydrate (HC) which contained similar ingredients except that the cornstarch content was increased to 20 per cent.

“Results show that the high carbohydrate supplemented with benfotiamine (HCB) diet resulted in significantly higher final average body weight, weight gain specific growth rate, and significantly better food conversion ratio than the values for both C and HC groups,” the authors said.

Fast growth contributes to higher survival rates. “This allows the young fish to attain a certain size that enables them to somehow ‘discourage’ predators to go after them and thus, escape from them,” corresponding author Dr. Augusto Serrano Jr., explained to Hatchery International.

Supplementing fry diet with benfotiamine and, to some extent, thiamine, enhances the whole process of glucose utilization partly for energy and partly for storage as fat.  Almost all aquatic animals are considered ‘diabetics’ because of the inability of their system to allow blood glucose to enter their body cells.

Serrano stressed, “Body fat storage in young fish is very important for their survival during the transition from nursery to grow out. A more important aspect of dietary incorporation of benfotiamine is the enhancement of resistance to adverse conditions such as higher salinity, temperature, ammonia toxicity among others.”

On top of producing quality juveniles, supplementation of benfotiamine could also bring down feed costs.  With its protein sparing effect of dietary carbohydrates and attractability, feed manufacturers for catfish may cut down the feed costs. 

“This means that they could reduce the proportion of dietary protein perhaps by about five per cent or less and replace it with dietary carbohydrates, which are a lot cheaper. Since benfotiamine is a processed thiamine, a vitamin for all animals, there is no risk or very negligible risk, if any, to the consumers,” he said.

Feeding strategies

In Nigeria, researchers from the Akwa Ibom State University said that mortalities in larval stages are mostly traced to poor feeding strategies.

“Fry need consistent and high-quality food provided in sufficient quantities at regular intervals for smooth transitional growth and satisfactory survival rate,” E. Ekong et al. said. “Therefore, to achieve desirable outcomes and improved rates, using high quality feeds and proper management techniques is inevitable.”

In their study, the test diet of a combination of spirulina and soybean trumped the control diet of fishmeal in African catfish larva. The research team from Akwa Ibom State University evaluated the effects on the diet on performance parameters.

The difference was most notable in weight gain. Cohorts in the test diet posted an increase of 2.42 grams while control had 1.28 grams. Survival rate in the test was 62 per cent. It was 52 per cent in control. It was noted that FM was not easily accepted by fry.

Tried-and-test encapsulated artemia as feed fits the description but high cost makes it beyond the reach of most of the growers in Nigeria. This has led the authors to identify an alternative larval diet with ingredients that are readily available and acceptable.

“Spirulina is considered one of the most concentrated natural sources for nutrition to both terrestrial and aquatic animals. Therefore, Spirulina could be an excellent source of useful nutrients as well as a good energy source that can be used as crucial component for animal feeding,” they said. 

On top of having high macro- and micro-nutrient contents, they said another strength of spirulina is that it grows in water and can be harvested and processed easily.

“Comparative study of fishmeal and a test feed on the growth and survival rate of Clarias gariepinus (African catfish) larvae” was published on Journal of Ecology and Natural Resources.

Neighbourhood pollutants

Still in Nigeria, external factors contributing to catfish welfare were considered by a team from the Michael Okpara University of Agriculture. P.A. Chinedu-Ndukwe et al. focused on effects of effluents discharged by beauty salons.

“It was concluded that hairdressing salon effluents had some negative effect on histopathology and behavioural responses of juvenile Clarias gariepinus.” the authors said in “Effect of Hair Dressing Salon Effluent on the Juveniles of African Catfish (Clarias gariepinus)”. This was published on African Scientist.

Tell-tale indicators in affected fish were observed: odd swimming patterns, jerk movements, bottom resting and loss of appetite. Post-mortem, there were histopathological changes in the liver and fills of the fish. 

With the practice of indiscriminate discharge of pollutants and the impact on water quality, the study said that both the government and private sectors should step in. 

“Management strategies should be developed, the populace should be informed about the adverse effects of effluents and the role they play in our immediate environment.”