African Catfish Larvae Research Articles

First data on the experimental evaluation of predation on Heterobranchus longifilis larvae (Siluroidei; Clariidae) by toad tadpoles (Bufo regularis)

An investigation was conducted under laboratory conditions to analyse the mechanisms of prey capture by tadpoles, Bufo regularis Reuss, and to determine the minimum size at which the predation pressure by tadpoles on the larvae of African catfish, Heterobranchus longifilis Val., becomes insignificant. It was observed that the tadpoles fed on the larvae by suction without any specific capture strategies regardless of their sizes. The predation pressure was very high (100% mortality) during yolk-sac absorption and reduced gradually as the larvae increased in size. Based on these results, it was suggested to transfer the fry into nursing ponds only when they have reached a size greater than 10 mm TL (5–7 days) so as to avoid their predation during the primary nursing phase.

The effect of supplemental ascorbic acid in enriched live food for Clarias gariepinus larvae at startfeeding

The effect of three dietary ascorbic acid (AA) concentrations, each applied via two feed types, on production characteristics and physiological condition of African catfish ( Clarias gariepinus) larvae has been assessed in two 10-day culture trials. Three treatments received only Artemia nauplii enriched with an experimental emulsion containing 0, 10, or 20% ascorbyl palmitate (AP) and yielding 530, 1200 and 1600 μg AA g −1 DW Artemia, respectively; the other three treatments were fed the same Artemia diets which were partially substituted by an artificial diet containing no vitamin C (ratio 20:80). No differences in survival could be observed; however, from day 6 onwards the 20%-AP group showed significantly better growth compared to the 0%- and 10%-AP treatments. For the cofeeding series, the same positive, but not significant, influence of vitamin C on dry weight was found. Moreover, the animals receiving the highest vitamin C supplementation displayed a considerably lower stress sensitivity than those of the 0%- and the 10%-AP groups, for both the 100%- and the 20%- Artemia series. These differences had occurred by day 2, which might be indicative of the importance of AA in early development. A second trial, which was a repetition of the first one, revealed the same tendencies; however, growth differences were smaller, probably due to the higher incorporation levels of AA obtained in the live diet (530, 1700 and 2300 μg AA g −1 DW) and in the catfish larvae. Growth results of both experiments were supported with data from the ultrastructural evaluation of the hepatocytes; i.e. a more organized cell compartmentation and better-structured cell organelles in the 20%-AP group of the Artemia series compared to the control are indicative of a more active metabolism. The slow growth in the cofeeding series was documented by the poor condition of the hepatocytes. In a third experiment it was verified that the growth effect of the 20%-AP boosted Artemia diet was the result of the extra AA incorporation and not of the concomitant palmitic acid (PA), which was set free after hydrolysis of AP in the Artemia nauplii, and which could possibly be used as a supplemental energy source. The three treatments were fed Artemia nauplii enriched with 0% AP, 12% PA and 20% AP, respectively. Growth and stress resistance of the latter group were significantly higher compared to the control and the PA-supplemented fish. To our knowledge this is the first evidence for the positive role of high dietary vitamin C levels (more than 1500 μg AA g −1DW) on larval development of an aquaculture species, and more specifically of C. gariepinus.

Observations on agonistic behaviour of Clarias gariepinus larvae and juveniles under different densities and feeding frequencies in a controlled environment

Ten-day-old African catfish larvae, Clarias gariepinus, were stocked in aquaria at 5, 13, 22, and 30 larvae per liter with fish at each density being fed three and six times per day over 35 days. Fish were fed with an artificial diet in excess of their satiation requirements at each feeding. Every week total length was determined for samples of 25 fish per tank and all fish were counted at weekly intervals. Behaviour patterns were categorized into timed behaviour (i.e. resting, swimming and browsing), and frequency events e.g. number of contacts, aggressive contacts and number of head or body attacks. Fish at the lowest density grew faster than fish at the other densities. Feeding frequency had no effect on growth. With increasing densities fish less frequently changed timed behaviour patterns while spending a greater percentage of the time swimming. Aggressive behaviour was highest at the lowest density but remained uninfluenced at densities greater than five fish per litre. The high feeding frequency provoked a higher rate of aggressive contacts than the low feeding frequency. A suggested explanation was that these fish were more often in anticipation of food and consequently more active between feedings. In summary, it was shown that density had an effect on duration behaviour patterns such as resting and swimming, while feeding frequency significantly influenced frequency events, in particular the rate of aggressive behaviour. The study contributes to an understanding of factors influencing C. gariepinus juvenile behaviour and suggestions for follow-up experiments are discussed.

Larval rearing of an African catfish,Heterobranchus longifilis, (Teleostei, Clariidae): a comparison between natural and artificial diet

Two feeding experiments were conducted to evaluate growth and survival rates of African catfish (Heterobranchus longifilis Valenciennes, 1840) larvae fed with different diets: live Artemia nauplii, frozen Artemia nauplii, live zooplankton (Moina micrura), frozen zooplankton (Moina micrura), a dry diet based on yeast powder and beef liver, and a commercial trout starter diet. The larvae were fed in excess, six times per day every 4 hours, from the onset of exogenous feeding up to an age of 14 days. In both experiments the final mean weight and specific growth rate of fish fed live Artemia nauplii were significantly higher than those of fish fed other diets (p > 0.05). Survival rates of fish fed Artemia (live or frozen), Moina micrura (live or frozen) and dry diet did not significantly differ (p > 0.05) and ranged from 79 to 92% and 61 to 73% for experiment 1 and experiment 2, respectively. The commercial trout diet led to significantly lower growth and survival rates in comparison to all other diets tested. Although it led to a lower growth rate than that obtained with Artemia, Moina micrura proved suitable for first feeding of H. longifilis larvae. Locally available in West African waters, this cladocera could constitute a valuable alternative for larval rearing when a shortage of Artemia is expenenced. The results also showed that the artificial feed based on yeast powder and beef liver leads to survival rates as high as those obtained with living diets and thus represents a promising way for feeding H. longifilis fry. However, further studies on the nutritional requirements of the larvae remain necessary in order to improve the efficiency of dry diet in terms of growth performance.

A Comparative Study on the Use of Different Preparations of Decapsulated Artemia Cysts as Food for Rearing African Catfish (Clarias gariepinus) Larvae

AbstractAfrican catfish (Clarias gariepinus) larvae were fed on five preparations of decapsulated Great Salt Lake Artemia cysts: 1) dried (35C, 6h) and UV‐irradiated cysts; 2) heated cysts (80C, 10 min); 3) brinedehydrated and UV‐irradiated cysts; 4) micro‐bound diet 1 (with intact decapsulated cysts used in diet preparation 1); and 5) micro‐bound diet 2 (with crushed and shited decapsulated cysts used in diet preparation 1). The larvae were fed from the first day after yolk‐sac resorption (fourth day after hatching). After a 14‐d rearing period, larvae fed on dried or heated decapsulated cysts yielded significantly higher mean weights than the groups fed on brine‐dehydrated decapsulated cysts or micro‐bound diet 1. Feeding micro‐bound diet 2 resulted in a significantly lower average gain in weight as compared to the other groups.

Controlled hatchery production of Clarias gariepinus (Burchell 1822): growth and survival of fry at high stocking density

. The mean increase in African catfish, Clarias gariepinus (Burchell), weight with time over the entire larval period can be approximated by a cubic or exponential growth model. However, the growth rate indices specific growth rate (k) and the regression coefficient of a cube root transformation of the weight data (b), both vary significantly when measured over successive short intervals from first feeding. In particular, the onset of air breathing is associated with a significant depression in growth rate. The variation in specific growth rate (k) with larval age closely approximates the relationship between mean % increase in body weight per day and larval age; however, the cube root regression coefficient does not share this property. In addition to the effect of larval age the growth rate of African catfish larvae is significantly affected by the initial density at which they are stocked (between 25 and 250 larvae/1) and interactions between age and stocking density. Survival over the larval period, of 80% or more, is apparently unaffected by initial stocking density (between 50 and 250larvae/I); however, the onset of air breathing in particular is associated with an increase in fish deaths.

Effects of salinity on growth and survival of African sharptooth catfish (clarias gariepinus) larvae

Summary Growth and survival of replicate batches of African sharptooth catfish (Clarias gariepinus) larvae were monitored in 0, 2.5, 5.0, 7.5 and 10 ppt salinity. No significant differences in mortality or growth rate were evident between 0 and 5 ppt salinity. At 7.5 ppt mortality rate was higher and larval growth rate declined in comparison to the lower salinities. At 10 ppt all larvae died within 48 hours. The condition factor of the larvae similar between 0–2.5 ppt and displayed a declining trend between 2.5–7.5 ppt. Osmoconcentratkm of blood plasma of C. gariepinus in fresh water was 280 ± 20 mOsm/kg which is equivalent to 9.5 ppt salinity. It was concluded that 0–2.5 ppt is the optimal sclinity range for larval rearing and that short-term exposure to higher salinities (2.5–7.5 ppt) could be effective in the treatment of ectoparasitic diseases.

Temperature preferences and optimum temperature for growth of African sharptooth catfish ( Clarias gariepinus) larvae and postlarvae

The optimum temperature for the primary nursing of Clarias gariepinus larvae and postlarvae was experimentally determined using two complementary methods. Growth of larvae was monitored at different temperatures ranging from 22 to 33°C. The final temperature preferendum of juveniles was determined in a horizontal thermal gradient. High growth rates were recorded between 25 and 33°C and the best was at 30°C. Size variation of fishes reared at 22°C was significantly greater than those batches reared at higher temperatures. The final temperature preferendum was found to be 30°C which corresponds to the temperature at which highest growth rate was recorded, and it is concluded that this temperature is probably optimal for most physiological processes.

Quantitative feed requirements of African catfish ( Clarias gariepinus Burchell) larvae fed with decapsulated cysts of Artemia: I. The effect of temperature and feeding level

In a series of four experiments, the effects of temperature (range: 25.0–32.5°C) and feeding level on the growth performance and survival rate of first-feeding larvae of the African catfish ( Clarias gariepinus Burchell) was assessed. Feeding occurred with dried decapsulated cysts of Artemia. Growth performance was determined on the basis of growth rate, food conversion ratio, energy conversion efficiency, protein efficiency ratio, and apparent net protein utilization. A new approach to assess growth rate and feeding levels in larval nutrition studies is presented and discussed. The quantity of decapsulated Artemia cysts and the time needed to raise larvae of Clarias gariepinus up to a weight of 50 mg for different combinations of temperatures and feeding level were determined. Recommendations are made for optimal temperature and feeding level under practical farming conditions.