Effect of dietary lipid level on growth and feed utilization in cultured South African abalone Haliotis midae L. fed diets with a constant protein‐to‐energy ratio

The aim was to test whether abalone growth and feed conversion ratio (FCR) could be maintained at increased dietary lipid levels if the protein:energy ratio (P:E) was kept constant. Two size classes (25–30 and 65–70 mm) of Haliotis midae were fed diets with graded levels of lipid (4–16%), in which total protein varied (34–39%) to maintain a constant P:E (22 g protein MJ^?1). For both size classes, overall performance was best on diets containing 4% and 7% lipid. Above 7% lipid, specific growth rate, shell length increment and protein efficiency ratio decreased while feed consumption and FCR increased significantly. The observed deterioration in growth and nutritional performance in diets with >7% dietary lipid was more marked in the 65–70 mm size class than in the 25–30 mm class, indicating that the smaller size class were better equipped to metabolize higher levels of dietary lipid. We concluded that the observed decrease in growth and feed utlization with the increasing dietary lipid was not due to an imbalance of dietary protein relative to energy, but rather that H. midae is unable to effectively utilize lipids as an energy source at levels in excess of 7% due to inherent physiological constraints.     

Optimum dietary crude protein level for growth in South African abalone (Haliotis midae L.)

A 95‐day feeding trial was conducted to evaluate the effects of dietary crude protein level on total body weight gain and protein gain of juvenile (4.89 ± 0.57 g) South African abalone (Haliotis midae). Six semi‐purified diets containing casein, fish meal and cottonseed meal as protein sources, and with crude protein levels ranging from 54.8 to 479.2 g kg^?1 dry matter (DM), were fed to four tanks containing 30 abalone each in a continuous flow system. No differences (P > 0.05) were found in moisture, ash or lipid content of soft‐body tissue as dietary crude protein level increased, indicating that differences (P < 0.05) in soft‐body protein content were solely due to dietary crude protein level. The relationships between dietary crude protein level and total body weight gain and protein gain were analysed by broken‐line and second‐order polynomial regression models. Based on total body weight gain, 358.7 g kg^?1 DM dietary protein from good quality sources is recommended for maximum growth of juvenile H. midae, while, if dietary protein is reduced to 280.7 g kg^?1 DM, growth will be depressed with 5 g kg^?1.     

Parentage assignment in Haliotis midae L.: a precursor to future genetic enhancement programmes for South African abalone

The establishment and evaluation of family lines using pedigree information provides an advanced understanding of the variability that exists for complex, economically valuable traits and is a necessary step in the execution of an effective breeding programme. The aim of this study was to assign parentage to mass‐spawned Haliotis midae juveniles using species‐specific microsatellite markers. Screening of wild abalone individuals revealed that the nine loci selected complied with the minimum requirements for parentage analyses: a null allele frequency <5% as well as a high number and frequency of alleles per locus. A total of 598 individuals were genotyped (198 breeding individuals and 400 F1 progeny) from two farms, with parentage results yielding 91% and 90% successful assignment for Farms A and B respectively. This study, therefore, provided the necessary pedigree information required for controlled breeding of individual adult abalone and indicated the usefulness of the panel of microsatellite markers selected for parentage assignment.     

Evaluation of an in vitro digestibility technique for the prediction of protein digestibility in the South African abalone, Haliotis midae L.

A pH-stat multienzyme in vitro digestibility assay was investigated for its efficacy in predicting apparent protein digestibility coefficients in abalone diets. Linear regression analysis between in vitro digestibility estimates and in vivo digestibility coefficients obtained from abalone, revealed that the technique could be used to reliably predict apparent protein digestibility. Maximal predictability of the system was obtained when protein sources were analysed according to origin – animal or plant. The technique was used to assess the apparent protein digestibility of 34 potential protein sources for use in formulated feeds for Haliotis midae .     

The effect of free ammonia nitrogen,pH and supplementation with oxygen on the growth of South African abalone,Haliotis midae L. in an abalone serial‐use raceway with three passes

The farming of abalone, Haliotis midae L., can be intensified in serial‐pass systems, but water re‐use increases the concentration of NH₃ (free ammonia nitrogen, FAN) and reduces water pH. Changing the percentage dietary protein from 33% to 26% reduced the concentration of FAN (F_{42, 252} = 2.79; P < 0.0001) in a serial‐pass system and did not reduce weight gain (F_{1, 12} = 1.09; P = 0.31) or length gain (F_{1, 12} = 1.08; P = 0.31). Low water pH was the most important variable to contribute to a reduction in abalone growth (weight gain: F_{1, 19} = 64.5; P < 0.0001; r² = 0.76; length gain: F_{1, 19} = 41.9; P < 0.0001; r² = 0.67). In addition, supplemental oxygen (103% saturation) improved length gain (t = 3.45, P = 0.026) in abalone exposed to an average FAN concentration of 2.43 ± 1.1 μg L^?1) and an average pH value of 7.6 ± 0.13, relative to a treatment with no oxygen supplementation. Thus, in an abalone serial‐use raceway with three passes, FAN was not the first growth‐limiting variable. It is suggested that future studies should examine the major causes of reduced water pH in serial‐use systems and their effect on the growth and health of H. midae.     

Apparent and true availability of amino acids from common feed ingredients for South African abalone (Haliotis midae L.)

Apparent (APD) and true (TPD) protein digestibility and apparent (AAAA) and true (TAAA) amino acid availability of fish meal and plant protein ingredients utilized in the South African animal feed industry (corn gluten meal, soya bean meal, cottonseed meal, sunflower meal, canola meal, peanut meal, lupins and faba beans), incorporated at 450 g kg^?1 into single protein diets, were determined with juvenile South African abalone (Haliotis midae). Soya bean meal (96.34%) and lupins (96.51%) presented the highest APD values, with corn gluten meal (76.08%) the lowest value, while values for sunflower meal (92.21%), canola meal (93.94%) and faba beans (93.17%) were above 90%. APD values for cottonseed meal (86.28%) and peanut meal (86.73%) were comparable with that of fish meal (82.94%). A correlation coefficient (r) of 0.99 was found between ADP and mean AAAA. Furthermore, amino acid availabilities were relatively consistent within various feed ingredients. The mean amino acid secretion from a protein‐free diet was 19.08 mg 100 g^?1 dry diet, resulting in a mean increase of 1.88% units over all feed ingredients when comparing TAAA with AAAA. Calculated APD according to APD coefficients determined with single protein diets underestimated determined APD in several compound diets by 1.10–6.50%, while mean AAAA was underestimated by 6.93%.     

Dietary phosphorus leaching and apparent phosphorus digestibility from different inorganic phosphorus sources for South African abalone (Haliotis midae L.)

The objective of this study was to determine phosphorus leaching of diets supplemented with various inorganic phosphorus sources [mono basic sodium phosphate (MSP), mono basic calcium phosphate (MCP), a 3 : 1 mixture of mono and dibasic calcium phosphate (MDCP), dibasic calcium phosphate (DCP)], and the apparent phosphorus digestibility of these sources in Haliotis midae. A trend of increased dietary phosphorus leaching from diet pellets with increased water solubility of sources was observed. MSP presented the highest (P < 0.05) phosphorus leaching (58.8%), while a value of 14.9% was obtained with DCP. Unexpectedly high phosphorus leaching (48.7% maximum) was obtained for a reference diet consisting of commercial feed ingredients (fish meal, soya bean meal, cottonseed meal) without any phosphorus supplementation. DCP presented a lower (P < 0.05) apparent phosphorus digestibility (27.9%) than MSP (66.5%), MCP (72.6%) and MDCP (66.3%). When dietary phosphorus leaching and apparent phosphorus digestibility were take into account, MDCP seems to be the most promising inorganic phosphorus source for inclusion in abalone diets. Further research should concentrate on minimizing dietary phosphorus leaching through feed preparation techniques.     

An assessment of the efficacy of two lysine microencapsulation techniques to determine the quantitative lysine requirement of the South African abalone, Haliotis midae L.

The quantification of the essential amino acid requirements of a species is a prerequisite to the formulation of biologically optimized diets. In this study, crystalline L -lysine was used in an attempt to determine the quantitative lysine requirement of juvenile Haliotis midae . Two microencapsulation techniques [gelatine/acacia and cellulose acetate phthalate (CAP)] were used to retard leaching of crystalline L -lysine incorporated into semipurified test diets. An assessment of the efficacy of the encapsulation techniques, revealed that despite effective lysine supplementation, H. midae fed semipurified test diets containing encapsulated crystalline L -lysine failed to promote significant improvements in either growth, feed or protein efficiency ( P  > 0.05). The failure of the crystalline L -lysine to illicit growth and nutritional responses is discussed.     

Water quality in a serial‐use raceway and its effect on the growth of South African abalone,Haliotis midae Linnaeus, 1758

To quantify the effects of serial‐use of water on abalone growth and feed conversion, this study describes water quality in a serial‐use raceway with seven passes. A flow index of 7.2–9.0 L h^?1 kg^?1 was estimated as the minimum value at which to grow 60–70 mm Haliotis midae, as weight gain (analysis of variance; F_{6, 14}=13.9, P<0.0001) and feed conversion ratio (Kruskal–Wallis test; H_{6, 21}=16.3, P=0.012) were significantly reduced at lower values. pH and dissolved oxygen concentration were positively correlated with the flow index (pH, r²=0.99; P<0.001; dissolved oxygen, r²=0.99; P<0.001), while free ammonia nitrogen (FAN) and nitrite were negatively correlated with the flow index (FAN, r²=0.99, P<0.001; Nitrite, r²=0.93, P<0.001). The concentration of nitrite increased throughout the experiment and may reflect the colonization of Nitrosomonas bacteria as water re‐use increased. Based on comparisons with growth and toxicity tests, it is suggested that low pH combined with growth‐limiting levels of FAN were the first variables limiting abalone growth in the serial‐use raceway.     

The effect of animal size on the ability of Haliotis midae L. to utilize selected dietary protein sources

The effect of animal size on the qualitative protein requirements of two size classes of Haliotis midae L. was assessed by feeding 12 semi‐purified single protein test diets (20% protein, 6% lipid) to juvenile and young adult animals (10–20‐ and 40–50‐mm initial shell length). The protein sources selected for the trial comprised four fishmeals, casein, spirulina, abalone viscera silage, brewery waste, torula yeast, carcass, sunflower and cotton seed meals. The results indicated that in terms of growth and feed efficiency, the fishmeals and spirulina were the most suitable candidates for use as primary protein sources in formulated feeds, and with the exceptions of the carcass meal and brewery waste, the remaining protein sources demonstrated promise as partial primary protein source replacements. Mean growth rates for the large and small abalone over the experimental period were 1.45 and 1.24 mm month^?1 respectively. With respect to the larger size class of abalone, the smaller abalone displayed significantly reduced growth (F = 64.7, P < 0.0001), feed conversion ratio (F = 16.6, P < 0.0001) and protein efficiency (F = 26.8, P < 0.0001). Two‐way analysis of variance revealed significant interactions between protein source, animal size and feed conversion ratio (F = 2.4, P < 0.01) and growth (F = 5.4, P < 0.05), thus indicating that qualitative differences exist between the dietary protein requirements of the juvenile and young adult abalone.     

The effects of elevated pCO2 on growth,shell production and metabolism of cultured juvenile abalone,Haliotis iris

Reduced seawater pH and elevated pCO₂ are important considerations in tank‐based abalone aquaculture, while sea‐based farms may be at risk to ocean acidification reductions in pH. Juvenile Haliotis iris (5–13 and 30–40 mm shell length) were reared in two, 100‐day experiments at ambient pH_nbs (~ 8.1, 450 μatm CO₂), pH 7.8 (~1000 μatm CO₂) and pH 7.6 (~1600 μatm CO₂). Seawater pH was measured and adjusted automatically by bubbling CO₂ into water in replicated flow through tanks. Two separate trials were run, in winter (8.8°C) and summer (16.5°C). Survival and growth were monitored every 30 days, and post experiment measurements of morphometrics and respiration rate undertaken. Growth of shell length and wet weight were negatively affected by reduced pH, with a 2 to 3‐fold reduction in growth of both size classes between ambient and pH 7.6 treatments in the summer experiment. For small juveniles, growth reductions were in conjunction with decreases to shell weight, while large juveniles showed greater resilience in shell production. No changes to respiration rate occurred, suggesting that juveniles may maintain physiological functioning while tolerating dissolution pressure or that they are unable to upregulate metabolism to compensate for pH effects. These data show that CO₂ driven reductions in pH can impact growth, metabolism and biomineralization of abalone, and indicate that water quality and ocean acidification are of importance in aquaculture of the species.     

Protein and energy nutrition of brook trout (Salvelinus fontinalis) at optimal and elevated temperatures

The digestible protein (DP) and digestible energy (DE) requirements for maintenance and growth of brook trout (Salvelinus fontinalis) were determined using a factorial model at either optimum (15 °C) or elevated temperature (19 °C). Several key parameters of the factorial model were measured using a series of inter‐related studies. The maintenance requirements for DP and DE were 0.10 gDP kg^?0.69 day^?1 (15 °C) and 0.31 gDP kg^?0.78 day^?1 (19 °C), and 34.86 kJDE kg^?0.84 day^?1 (15 °C) and 46.14 kJDE kg^?0.86 day^?1 (19 °C). The total requirements for DP were 0.10 gDP kg^?0.69 day^?1 + 2.14PG (protein gain) (15 °C) and 0.31 gDP kg^?0.78 day^?1 + 1.98PG (19 °C). The total requirements for DE were 36.86 kJDE kg^?0.84 day^?1 + 1.58EG (energy gain) (15 °C) and 46.14 kJDE kg^?0.86 day^?1 + 1.64EG (19 °C). The partial efficiencies for growth were 0.47 (15 °C) and 0.51 (19 °C) for protein, and 0.63 (15 °C) and 0.61 (19 °C) for energy. Nutrient gain was lower at the elevated temperature; however, feed formulation for brook trout should be adjusted to match changes in nutrient requirements at different culture temperatures. The protein and energy requirements model will be useful for developing commercial feeds and feeding charts for brook trout.     

The growth and carbon allocation of abalone (Haliotis discus hannai) of different sizes at different temperatures based on the abalone‐kelp integrated multitrophic aquaculture model

The integration of shellfish and seaweed is an important and successful IMTA model. The IMTA of abalone and kelp has been well‐practiced in Sanggou Bay, China. In the present study, the growth and carbon allocation of abalone (Haliotis discus hannai) of different sizes (S, small; M, medium; L, large) fed kelp (Laminaria japonica) were investigated at different temperatures (10, 14, 18 and 22°C). A two‐way ANOVA showed that both size and temperature significantly affected the specific growth rate (SGR), food consumption (FC), feed conversion ratio (FCR) and apparent digestion rate (ADR) of abalone (p < 0.05), and significant interactions between the two factors were detected (p < 0.05). Curve estimation showed a significant quadratic relationship between SGR and temperature in each size class (p < 0.05). The two‐way ANOVA also showed that both size and temperature significantly affected all the measures of carbon allocation (p < 0.05) except for the carbon lost in metabolism (p > 0.05). All the measures of carbon allocation increased with the increasing temperature. It was concluded that it was better to culture H. discus hannai with a body weight less than 15 g at 20–22°C, and more than 15 g at 15–20°C to achieve good growth. The growth carbon of kelp around the abalone farm should be more than the metabolic carbon expenditure, which means the growth of kelp around the abalone farm should be more than 23.06%–61.91% of food consumption to maintain a carbon sink IMTA system without any carbon release.     

Broodstock diet with water and astaxanthin improve condition and egg output of brood fish and larval survival in Atlantic cod,Gadus morhua L.

Broodstock of Atlantic cod were fed with three diets; astaxanthin supplemented (100 ppm kg^?1) hydrated diet (30% water) (HWHAs), no additional astaxanthin supplemented (50 ppm kg^?1) hydrated diet (30% water) (HWLAs) and a control diet (50 ppm kg^?1 astaxanthin and 10% water). Throughout the spawning period, eggs were collected daily and fertilization success and proportion of embryos with normal cleavage were recorded. Larvae were reared using standard culture methods. Larval growth was recorded every 10 days and larval survival was recorded at 50 days post hatch. In general, broodstock fed with diets containing higher water content (HWHAs and HWLAs) and higher astaxanthin (HWHAs) had higher egg production and efficiency of egg output, lower egg incubation mortality and higher larval growth and survival. Broodstock fed with higher water content diets consumed less feed compared to control group. Also, broodstock fed with HWHAs and HWLAs recovered faster in terms of body condition than the control group. The egg bound mortality of female fish was significantly higher in control broodstock compared to broodstock fed with HWHAs and HWLAs. Broodstock fed with higher astaxanthin (HWHAs) had significantly higher fertilization success than other two groups however; no differences were found in proportion embryos with normal cleavage among different groups. Larval survival was significantly higher in HWHAs broodstock compared to other two groups. Our results showed that increased water content and astaxanthin levels in the diet could improve the condition and fecundity of Atlantic cod broodstock.     

The role of dietary methionine concentrations on growth,metabolism and N‐retention in cobia (Rachycentron canadum) at elevated water temperatures

This study determined impacts of dietary methionine concentrations at two temperatures on growth, feeding efficiency and N‐metabolites in juvenile cobia. Methionine concentrations of the experimental diets were deficient (M9; 9 g/kg), sufficient (M12; 12 g/kg) and surplus (M16, 16 g/kg). Water temperature was normal (30°C) or elevated (34°C). Twenty cobia in triplicate tanks were fed the experimental diets for 6 weeks. Both methionine and temperature affected cobia's growth and feeding efficiency. Cobia fed M9 performed lower than the fish fed M12 and M16 diets. Additionally, cobia reared at 34°C performed poorer than at 30°C, probably due to lower voluntary feed intake in the fish reared at 34°C. Protein efficiency ratio and protein productive value in cobia fed M9 diet were less than M12 or M16 diets. This was confirmed with the improved retentions of indispensable amino acids (AAs). No interactions between methionine and temperature were observed in growth and protein accretion. At 30°C, CF improved, while HSI and VSI declined upon methionine supplementation levels. Of which an interaction between temperature and methionine was present. Plasma, muscle and liver free AA and N‐metabolites were affected by methionine and temperature. Furthermore, temperature affected cobia's lipid class composition, resulting in increased phospholipids and cholesterol at 34°C.