Peter J. Britz

The suitability of selected protein sources for inclusion in formulated diets for the South African abalone, Haliotis midae

Abstract Five protein-rich ingredients, casein, fishmeal, soya oil cake, Spirulina spp. and torula yeast, were fed to Haliotis midae in semi-purified diets to evaluate their suitability as practical feed ingredients in abalone diets. All diets contained 30% protein and 5% fat, except for the Spirulina spp.-based diet which contained 19% protein. Two algal diets, fresh Plocamium corallorhiza and dried Ecklonia maxima were fed as controls. Abalone fed on fishmeal and Spirulina spp.-based diets displayed significantly higher growth rates than those fed on diets containing soya oil cake, torula yeast, casein and E. maxima. Growth rates of abalone fed P. corallorhiza were significantly lower than those on any other diets. The feed conversion ratios of the formulated diets ranged from 0.7 for the casein-based diet to 1.0 for the torula yeast-based diet. These values were lower than those obtained for the abalone fed the seaweed control diets. Protein efficiency ratios of abalone fed the formulated diets ranged from 3.3 for the torula yeast-based diet to 6.5 for the Spirulina spp.-based diet. These values were higher than those obtained from abalone fed the seaweed control diets. It was concluded that fishmeal and Spirulina spp. algae are the most suitable proteins for inclusion in practical diets for H. midae.

Effect of temperature on growth, feed consumption and nutritional indices of Haliotis midae fed a formulated diet

Abstract Commercial farmers using formulated feeds need to know what ration size to feed their abalone. In two growth trials the effect of temperature and abalone size on growth rate and nutritional indices of abalone fed a dry formulated diet was quantified. Between 12 and 20 °C growth rate and feed consumption increased, protein-efficiency ratio (PER) improved and FCR did not differ significantly. However, between 20 and 24 °C, growth and feed consumption declined sharply, and PER and FCR deteriorated. The condition factor of abalone decreased with increasing temperature. It was concluded that temperatures between 12 and 20 °C are physiologically optimal for H. midae. This range corresponds to the mean sea temperature range experienced by H. midae within its natural range. Feed consumption, expressed as a percentage of body weight per day, decreased with increasing abalone size. A model which predicts feed consumption as a function of temperature, shell length and feed-conversion ratio was developed.

Effect of dietary protein and energy level on growth and body composition of South African abalone, Haliotis midae

Abstract The effect of dietary protein and energy level on growth rate, nutritional indices and body composition of two size classes of Haliotis midae was investigated. Diets were formulated to contain three levels of protein (24, 34 and 44%), each with three levels of fat (2, 6, and 10%), to produce diets with estimated protein energy (PE) ratios ranging from 14.5–32.0 mg/kJ. The rates of weight gain, nutritional indices and body composition of both the smaller (0.2-1.0 g) and larger (7.0–14.0 g) abalone were significantly affected by the levels of protein and energy in the diets. Moreover, the two size classes of abalone differed in their responses to the diets. Maximum growth was achieved at a higher dietary protein level in the larger abalone (44%) than the smaller abalone (34%). The protein content of the larger abalone soft tissue was higher (ca. 7%) than the smaller abalone. Irrespective of the lipid content, the percentage of protein deposited by the larger abalone was highest in those fed the 34 and 44% protein diets, whereas that of the smaller abalone was highest for the 24 and 34% protein diets. The condition factor (CF) of small abalone was significantly higher for those fed the 24% protein diets in comparison to those fed the 34 and 44% protein diets, whereas the reverse was found in the larger abalone. It was concluded that the larger abalone had a higher protein requirement than the smaller abalone. Diets containing the highest level of dietary fat (10%) produced significantly lower growth rates and efficiencies of protein deposition in comparison to abalone fed the diets containing 6 and 2% fat, however, these trends were more marked among the small abalone size class. In addition, the feed conversion ratio (FCR) of small abalone fed the 10% fat diets was consistently poorer, but this trend was not present among the larger abalone whose FCR improved with an increasing PE ratio. It was concluded that a dietary lipid level of 10% is too high for H. midae to maintain a maximal growth rate. Proximal analysis of abalone fed the experimental diets revealed that the PE ratio of the diet as well as abalone size significantly affected the carcass composition.

Effect of dietary protein level on growth performance of South African abalone, Haliotis midae, fed fishmeal-based semi-purified diets

Abstract Starch-bound, semi-purified diets, using fishmeal as a protein source, were formulated to contain 27, 32, 37, 42 and 47% protein and fed to juvenile Haliotis midae . Weight gain was positively related to the level of dietary protein, increasing by 18% between 27% and 47% protein. Protein efficiency ratio was negatively related, declining from 3.2 to 2.3. Feed consumption rate was approximately 1 % of body weight per day for all diets. However, accurate definition of an optimal level of protein in formulated diets for abalone will only be possible once optimum dietary energy/protein ratios have been determined.

Comparative growth performance and digestive enzyme activity of juvenile South African abalone, Haliotis midae, fed on diatoms and a practical diet

Abstract The growth performance of juvenile South African abalone, Haliotis midae (3.22–11.29 mm shell length), fed diatoms and a pelleted, practical diet was evaluated. The growth of the juveniles did not differ significantly in terms of the increase in shell length (diatoms, 50 ± 7 μm day −1 ; pellets, 59 ± 9 μm day −1 ) and weight (diatoms, 1.66 ± 0.24% daily growth rate; pellets, 1.91 ± 0.27% daily growth rate). Abalone fed the pellets consumed 5.55 ± 0.20% of their body weight per day, feed conversion ratio was 0.44 ± 0.04, protein efficiency ratio 6.64 ± 0.77, and percentage protein deposited 32.64 ± 3.72%. Protease activity was significantly higher, and amylase activity significantly lower, in juveniles fed pellets in comparison with diatoms. Similar, but very low, levels of lipase activity were observed in juveniles fed both the practical diet and diatoms. The results show that the digestive physiology of juvenile H. midae can readily adapt to artificial diets, and that these can successfully replace natural diets.

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

Abstract 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.

Evaluation of different markers to determine apparent nutrient digestibility coefficients of feed ingredients for South African abalone (Haliotis midae L.)

Abstract Chromic oxide (Cr 2 O 3 ), acid-insoluble ash (AIA) and crude fibre were evaluated as inert markers in digestibility studies with Haliotis midae by calculating apparent dry matter, organic matter, energy, protein and amino acid availability for fish meal, soybean meal and cottonseed meal included at 30% into a reference diet. AIA was the only marker that yielded consistent realistic apparent digestibility coefficients (ADCs), which were comparable ( P >0.05) to values derived through total collection. Both Cr 2 O 3 and crude fibre in faeces were either lower or similar to their respective levels in feed, resulting in negative ADCs. Leaching of markers from the diets did not have an effect ( P >0.05) on digestibility coefficients. No difference ( P >0.05) was found in apparent dry matter digestibility between faeces voided either during the night or daytime. Washing of faeces with distilled water after collection had no influence ( P >0.05) on AIA content. In all test ingredients, mean apparent amino acid availability reflected apparent protein digestibility. Apparent digestibility of protein in fish meal (76%) by H. midae was within the range of values reported for fish species (62–91%). Soybean meal is a promising feed ingredient in abalone feeds due to the high apparent digestibility of its organic matter (79%), energy (83%), protein (85%) and both essential and non-essential amino acids (mean of 86%).

The effect of seven binding agents on 24-hour water stability of an artificial weaning diet for the South African abalone, Haliotis midae (Haliotidae, Gastropoda)

Abstract The 24-hour water stability of seven different binders for an abalone weaning diet were tested. They included five alginates in combination with two sequestrants, agar, gelatine and a mixture of agar/gelatine. The best water stability was obtained with a 1:3 agar/gelatine mixture which retained 70.7±2.7% of its dry weight after 24 h. A method of preparing this mixture is presented.

Influence of Varying Dietary Protein Content at Three Lipid Concentrations on Growth Characteristics of Juvenile Swordtails (Xiphophorus helleri Heckel 1848)

Three protein levels (30%, 38% and 45%) at three different dietary lipid concentrations (6%, 8% and 12%) were used to formulate nine different diets that were fed for 60 days to 6–8 weeks old juvenile swordtails (Xiphophorus helleri). It would appear that a diet of at least 45% protein at a 6% lipid concentration is needed for the best specific growth rate (1.27% per day) and feed conversion ratio (2.50) at this specific growth phase in X. helleri. No ‘protein sparing effect’ was found when lipid concentration was increased at lower protein levels.

Gastric evacuation time and digestive enzyme activity in abalone Haliotis midae fed a formulated diet

Gut evacuation time and enzyme activity were monitored over 46 h in juvenile Haliotis midae fed a formulated diet. Gut fullness peaked 6 h after feed was offered and returned to pre-feeding levels within 24 h. Enzyme secretion began with the onset of feeding and continued for at least 6 h after peak gut fullness was attained. Protease activity increased significantly following ingestion, whereas amylase activity was maintained at a fairly constant level. A low level of lipase activity was observed, suggesting that the ability of H. midae to digest fat is limited. When formulated food is used, a feeding frequency of once per day is recommended.