Growth Rate Of Abalone Research Articles

Growth and survival of juvenile abalone Haliotis diversicolor fed on brown macroalgal gametophytes, a potential alternative initial diet

To elucidate the dietary value of macroalgal gametophytes for post-larval and juvenile abalone Haliotis diversicolor, growth and survival rates of five different size groups of the abalone [1.4–3.4, 2.8–4.6, 4.4–6.0, 5.7–8.3 and 7.6–12.0 mm in shell length (SL)] fed on gametophytes of three brown macroalgae ( Eisenia bicyclis, Ecklonia cava and Undaria pinnatifida; Laminariales, Phaeophyta) were examined, and compared with those fed a benthic diatom Nitzschia sp. Most abalone actively fed on all algal diets, but large variations in the growth rate were observed among the diets and abalone growth stages. Mean growth rates of abalone fed Nitzschia sp. were similar or higher than those fed the macroalgal gametophytes in 1.4–4.6 mm SL, but lower in 4.4–8.3 mm SL. For all of the three macroalgal gametophytes, growth rates of the abalone increased linearly from 2–3 mm SL and were highest at around 6 mm SL. However, mean growth rates of larger individuals (7.6–12.0 mm SL) dropped to less than 45 μm day − 1 in all treatments with the macroalgal or diatom diets. These results indicate that gametophytes of the three brown algae are favorable diets for juvenile H. diversicolor of 3–8 mm SL. Introduction of the brown algal gametophytes as diets for juvenile H. diversicolor is considered to be an alternative innovative method to improve the efficiency and stability of the abalone culture.

Low-density culture of red abalone juveniles, Haliotis rufescens Swainson 1822, recirculating aquaculture system and flow-through system

Commercial abalone culture is carried out using flow-through systems with a high water volume exchange in Baja California, Mexico. The objective of this work was to compare the growth rate and survival of red abalone cultured in two systems. Flow through (daily water exchange rate of 800%) and recirculating systems consisted of a 250 L fibreglass tank and constant aeration, but biofiltration in the recirculating system was provided with a 28 L (1 ft3) bubble-washed bead filter. Water variables were measured either daily (dissolved oxygen, temperature, pH and salinity) or three times a week (total ammonia nitrogen, nitrate-nitrogen, nitrite-nitrogen and alkalinity). Shell length was measured every 2 weeks for 18 weeks. Only the alkalinity and pH were significantly different due to the addition of sodium bicarbonate to the recirculating system. Abalone growth rate was 26.1 ± 15.96 μm day−1 in the recirculating systems and 22.21 ± 18.69 μm day–1 in the flow-through systems. The final survival was 78.74% in the recirculating systems and 71.82% in the flow-through systems. Significant differences in the final size and survival of the abalones were found between systems (P<0.05). Therefore, recirculating aquaculture systems is a feasible alternative for juvenile red abalone culture.

Dietary value of gametophytes and juvenile sporophytes of the brown macroalga Eisenia bicyclis for juvenile abalone Haliotis diversicolor

The dietary value of juvenile stages (gametophyte and juvenile sporophyte) of the brown macroalga Eisenia bicyclis for post-larval and juvenile abalone Haliotis diversicolor of 2.0–6.5 mm in shell length (SL) was examined and compared with that of a benthic diatom, Nitzschia sp., in laboratory experiments. Most abalone actively fed on these diets, but there were large variations in the growth rate among the diets and among the growth stages of abalone. Growth rates of abalone fed on Nitzschia sp. were highly variable within each growth stage, but showed no clear differences among growth stages. In contrast, in abalone fed gametophytes or juvenile sporophytes, growth rates linearly increased as abalone grew. Growth rates of >60 μm SL/day were observed in juveniles of >3 mm SL fed gametophytes, and juveniles of >5 mm SL fed juvenile sporophytes. These results indicate that the dietary value of the juvenile stages of E. bicyclis for the abalone changes as they grow, and with growth juvenile abalone begin to efficiently utilize gametophytes and juvenile sporophytes in that order.

Effect of eight benthic diatoms as feed on the growth of red abalone (Haliotis rufescens) postlarvae

The growth rate of abalone post larvae of Haliotis rufescens fed ad libitum with a benthic monoalgal diatom culture maintained as monocultures on a semi-commercial scale, was evaluated and correlated with the biochemical composition of the diatoms. The cell size (7.0 × 4.0 µm to 21.0 × 7.5 µm), protein percentage (7.42% to 13.66%), and ash content (49.03% to 59.61%) were different among diatom strains; lipid percentage, nitrogen free extract, and energy content (Kcal g−1) were similar among diatom strains. The values of essential and non-essential amino and fatty acids composition differed among diatom strains. Differences in the abalone shell length and orthogonal analyses revealed postlarval growth was dependent on the quality of the food source. Postlarvae abalone displaying the longest shell lengths were fed Nitzschia thermalis var. minor and Amphiprora paludosa var. hyalina (1,712.0 ± 61 µm and 1,709 ± 67 µm, respectively), followed by Navicula incerta (1,413.3 ± 43 µm). The fatty acid content of benthic diatoms and abalone growth rate were not correlated.

NUTRITION REQUIREMENT OF CULTURED ABALONE POST LARVAE AND JUVENILES: A REVIEW

Abalone aquaculture attracts wide attention nowadays because of its high market value and depleted of wild stocks. China and Japan are the main producer of abalone from aquaculture followed by other countries such as New Zealand, Australia and US. Most of cultured abalone are temperate species but considerable research efforts have been made to culture tropical abalone in the Philippines, Thailand, and Indonesia. Most of abalone culture still depends on natural food but recent studies have been conducted to develop artificial diet for abalone. This will not only reduce wild harvest of macrolagae but also develop high nutrition diet at low cost. Successful abalone aquaculture is determined by correct nutrition supplement in the diet. As other cultured animal, abalone requires balanced nutrition of carbohydrate, protein, lipid, vitamins, and minerals. As herbivores, abalone can utilize carbohydrate efficiently as energy source and thus only requires low level of protein (range from 27%—40%). Lipid requirements range from 3%—5% while some minerals such as calcium and phosphorus in artificial feed are only needed in small amount, 0.5% of calcium in diets and 0.7% of phosphorus in the diet can improve the growth rate of abalone. There is not available information of vitamin upplementation in the diet but it is suggested that natural food meets the requirement.

THREE ALGAL PROPAGATION METHODS ASSESSED TO CREATE A RHODOPHYTA DIET FOR JUVENILE GREENLIP ABALONE (HALIOTIS LAEVIGATA) IN THE LATER NURSERY PHASE

A variety of red algal species have been identified as potential food sources for juvenile Greenlip Abalone, Haliotis laevigata (>5 mm shell length). To provide the red algal species in a diet suitable for juvenile abalone three propagation methods; spore production, protoplast isolation, and fragment culture were investigated. The potential algae requirements and consumable costs for each propagation method were determined, using experimental data and values from the literature, to assess the viability of utilizing each of these propagation methods in a commercial abalone nursery. The use of red algal spores required 592-52,000 kg of algae, depending on the level of spore release and the percentage of fertile algal thalli collected. Protoplast isolation reduced the amount of algal biomass to 8.55-910 kg but was affected by the efficiency of the isolation procedure. Even at an efficient production of 1 3 10 8 protoplastsg -1 wet weight alga the cost of consumables (enzymes) was $US 13,576. A feeding trial utilizing Laurencia sp. fragments adhered to the plates using agar, produced juvenile abalone growth rates comparable to those obtained with the current commercial nursery diet of the green alga Ulvella lens plus the diatom Navicula cf. jeffreyi. The Laurencia fragments did not regenerate on the plates so it was reapplied weekly, which is not feasible on a commercial scale because it would require 10.6 t of Laurencia and 443 kg of agar at a cost of $US 34,899. Gracilaria sp. fragments were able to regenerate with a growth rate of 4.42%� day -1 and therefore the algal fragments would only need to be applied to the PVC plates once, at the start of the later nursery phase (5 mm SL), reducing the amount of algal biomass to 432 kg. We therefore conclude that regenerating fragment culture (fragments <1 mm) is the only method that could successfully produce red algal diets for juvenile abalone on a commercial scale in the later nursery phase.

A Comparison of Various Seaweed-Based Diets and Formulated Feed on Growth Rate of Abalone in a Land-Based Aquaculture System

The effects of different diets on growth in the cultured South African abalone, Haliotis midae (Linnaeus), was investigated. Growth of juvenile Haliotis midae was monitored on a commercial abalone farm over a period of 9 months in an experiment consisting of 9 treatments with 4 replicates (n = 250 individuals per replicate). The treatments were: fresh kelp (Ecklonia maxima) blades (seaweed control); Abfeed® (formulated feed control); kelp + Abfeed® dried kelp pellets; dried kelp blades; dried kelp stipes; fresh kelp with the epiphyte Carpoblepharis flaccida; a mixed diet (Gracilaria gracilis, Ulva lactuca, and kelp) and a rotational diet (abalone were fed 1 of the 9 treatments for the first week and them kelp for the next 3 weeks). Results show that abalone grow well on all fresh seaweed combinations, but grow best on a mixed diet. The likely reason for the success of the mixed diet is that the red and green seaweed was farm grown, with an increased protein content. Dried kelp in any form produced poor growth. Abalone fed on the mixed diet grew at 0.066 mm day−1 shell length and 0.074 g day−1 body weight; this corresponds to 24.09 mm shell length and 27.01 g body weight increase per annum. Abalone fed on dried kelp grew at only 0.029 mm day−1 shell length and of 0.021 g day−1 body weight. Abalone grown on Abfeed® grew at 0.049 mm day−1 shell length and 0.046 g day−1 body weight which corresponds to 17.88 mm and 16.79 g increase per annum; this is better than the dried seaweed feeds, but poorer than the fresh seaweed combinations. This study shows that seaweed diets, particularly if the diets include seaweeds grown in animal aquaculture effluent, are good substitutes for the formulated feed generally used today.

Suitability of three red macroalgae as a feed for the abalone Haliotis tuberculata coccinea Reeve

A 60-day feeding trial was conducted to assess the suitability of three red algae, Hynea spinella, Hynea musciformis and Gracilaria cornea, as potential feed for the culture of juvenile abalone, Haliotis tuberculata coccinea R. Seaweeds were reared in a biofiltration unit with fishpond waste water effluents. The three algal species were found to contain high protein contents which would be related to its production under the high nitrogen culture conditions of the biofilter system. Protein and carbohydrate contents were highest in H. musciformis and lowest in G. cornea. Survival rates of juvenile abalone were very good, regardless of the algae fed. Feed intake of H. spinella was highest, followed by H. musciformis. Growth rates of abalone were within the range obtained under commercial conditions, final shell length and weight being significantly highest in animals fed H. spinella and lowest in those fed G. cornea. Feeding G. cornea lead to the lowest growth performance due to the lowest feed intake, whereas feed conversion ratios were significantly highest for H. musciformis and protein efficiency ratios were higher for both H. spinella and G. cornea. This study suggested the good potential of any of the three red seaweeds tested—successfully produced by the biofilter system, their nutritional composition being similar to other macroalgae used as feed for abalone and matching the abalone protein and lipid requirements—hence promoting growth and survival. Nevertheless, the biofilter produced macroalgae H. spinella showed the highest dietary value for juvenile of H. tuberculata coccinea.

Effects of starvation and dietary lipid on the lipid and fatty acid composition of muscle tissue of juvenile green abalone ( Haliotis fulgens)

Lipid metabolism of juvenile abalone, either starved or fed diets containing either 3.0 (HL) or 0.12% (LL) lipid, was investigated. Abalone were initially fed a nutritionally balanced formulated diet. Both PUFA and HUFA were low in the experimental formulated diets. After 60 days, growth rates of abalone fed the formulated diets were low and probably reflective of a lack of sufficient essential fatty acids. However, the total lipid content of the muscle tissue of abalone fed diets LL and HL remained unchanged from that of the start of the experiment. However, the level in the starved abalone was significantly higher (21.5%) than that of abalone at the start of the experiment. The percentage of polar lipid and neutral lipid in the abalone muscle tissue ranged from 70.8% to 76.1% and 23.9% to 29.2%, respectively. Levels of 20:4n-6, 20:5n-3 and 22:5n-3 in the polar lipid of the muscle of the starved abalone significantly increased while levels of 20:4n-6 and 20:5n-3 in the neutral lipid for abalone in all treatments decreased, suggesting the essentiality of these HUFA. Levels of 20:5n-3 and 22:6n-3 in the polar lipid of the tissue of the starved abalone were significantly higher than the levels of these respective fatty acids in the abalone fed diets HL and LL. These higher levels probably reflect the weight loss associated with starvation combined with lipid not being used as an energy source. More research directed toward the determination of the fatty acid requirements of postlarvae and for successful maturation and a spawning of abalone needs to be conducted.

Diet development and evaluation for juvenile abalone, Haliotis asinina: animal and plant protein sources

Growth studies were conducted to determine the suitability of animal and plant protein sources in the diet of abalone, Haliotis asinina. Juvenile abalone with mean initial weight and shell length of 0.69±0.04 g and 11.4±0.35 mm, respectively, were fed practical diets for 84 days at a temperature range of 28–31 °C. The practical diets contained 27% crude protein from various sources such as fish meal (FM), shrimp meal (SM), defatted soybean meal (DSM), and Spirulina sp. (SP). A formulated diet (diet 1) served as the control. The diets were fed to abalone at 2–5% body weight once daily at 1600 h. Weight gain (WG), increase in shell length (SL), specific growth rate (SGR), protein efficiency ratio (PER) and feed conversion ratio (FCR) were evaluated. Highest weight gain (WG: 454%) was attained with abalone fed diet 2 with protein sources coming from a combination of FM, SM, and DSM. This value was, however, not significantly different ( P<0.05) from those fed diets 4 and 1 (Control diet) with protein sources coming from FM, SM, SP and FM, DSM, SM, respectively. Abalone fed diet 3, which used both plant protein sources, DSM and SP, showed significantly lower WG (327%). Survival was generally high ranging from 85% to 100% for all treatments. The SGR showed the same trend as the percent weight gain. The FCR and PER obtained, however, were not significantly different for all treatments. The amino acid profile of diets 1, 2, and 4 simulated that of the abalone protein, which could have been a contributing factor to the higher growth rate of abalone fed these diets. Diet 3, which contained only plant protein sources, showed relatively lower methionine values compared with the abalone muscle tissue. Although abalone are considered herbivorous animals, results of this study indicate that a combination of dietary plant and animal protein sources was necessary to attain the best growth rate.

NITROGEN ENRICHMENT OF PORPHYRA PERFORATA THROUGH HIGH DOSE PULSE FERTILIZATION

Zertuche‐González, J. A1., Chanes‐Miranda L2., Carmona, R3., Kraemer G4., Chopin T.5 &amp; Yarish, C3 1Universidad Autonoma de Baja California, Instituto de Investigaciones Oceanologicas, PO Box #453, C.P. 22830, Ensenada, Baja California, Mexico. 2CBTIS‐41, Km 115 Carretera Transpeninsular, Ensenada, BC Mexico. 3University of Connecticut, Department of Ecology and Evolutionary Biology, 1 University Place, Stamford, CT, 06901‐2315, USA. 4State University of New York, Purchase College, Div. of Nat. Sciences, Purchase, NY, 10577, USA. 5University of New Brunswick, Centre for Coastal Studies and Aquaculture and Centre for Environmental and Molecular Algal Research, P.O. Box 5050, Saint John, New Brunswick, E2L 4L5, CanadaPorphyra perforata is a highly preferred seaweed used as fodder in abalone culturing due to its relatively high nutritional value. High growth rates of abalone, particularly in the early stages, are suspected to be due the high protein‐aminoacid and low water content of the Porphyra. Also, high NO3 content may be important to improve the bacterial flora in the animals, which in turn may favor more efficient digestion. Changes in the composition of Porphyra, however, can occur rapidly due to environmental conditions decreasing the nutritional value of the plant. Short term N pulse fertilization were performed on P. perforata in order to evaluate the feasibility to increase its nutritional value. Enrichment was performed under low light conditions (&lt;5 μE m‐2 s‐1) to inhibit growth and promote higher N enrichment per unit of biomass. Tissue N in the form of NO3, NH4 and total organic N were measured, after 3,6,12 and 24 hrs, in tissue exposed to 500 μM of N. Results indicated a rapid N tissue enrichment particularly in the form of NO3. Nitrate accumulation occurs continuously, up to 24 hrs. Total organic N is maximum after 12 hrs and tends to decrease after that. Fertilization with NH4 promotes NO3 accumulation. These results suggest the feasibility to improve the nutritional value of P. perforata by short‐term pulse fertilization. The capacity of this species to uptake NH4 under low light conditions (similar to those use in abalone culturing) makes it also ideal for integrated aquaculture.

A sustainable integrated system for culture of fish, seaweed and abalone

A 3.3 m 2 experimental system for the intensive land-based culture of abalone, seaweed and fish was established using an integrated design. The goals were to achieve nutrient recycling, reduced water use, reduced nutrient discharge and high yields. Effluents from Japanese abalone ( Haliotis discus hannai) culture tanks drained into a pellet-fed fish ( Sparus aurata) culture tank. The fish effluent drained into macroalgal ( Ulva lactuca or Gracilaria conferta) culture, and biofilter tanks. Algal production fed the abalone. The system was monitored to assess productivity and nitrogen partitioning over a year. The fish grew at 0.67% day −1, yielding 28-kg m −2 year −1. The nutrients excreted by the fish supported high yields of U. lactuca (78-kg m −2 year −1) and efficient (80%) ammonia filtration. Gracilaria functioned poorly. Ulva supported an abalone growth rate of 0.9% day −1 and a length increase of 40–66 μm day −1 in juveniles, and 0.34% day −1 and 59 μm day −1 in young adults. Total abalone yield was 9.4 kg year −1. A surplus of seaweed was created in the system. Ammonia-N, as a fraction of total feed-N was reduced from 45% in the fish effluents to 10% in the post-seaweed discharge. Based on the results, a doubling of the abalone:fish yield ratio from 0.3 to 0.6 is feasible.

Co-culture of dulse Palmaria mollis and red abalone Haliotis rufescens under limited flow conditions

A series of experiments was conducted to determine factors limiting the stocking density and growth rates of red abalone in a co-culture system with the macroalgae dulse ( Palmaria mollis). Co-culture conditions were altered by varying the degree of artificial illumination (0 h, 12 h at night, and 24 h d −1 in addition to ambient sunlight) used to supplement ambient sunlight and water volume exchange rate (1, 6, or 35 d −1). Rates of dulse production, dulse consumption by abalone, ammonia uptake by dulse and ammonia excretion by abalone were measured seasonally over 1 year. Abalone growth rates under co-culture conditions were measured. Maximum abalone stocking densities within the co-culture system were first limited by the amount of algae available for abalone consumption, and then by the capacity of the algae to absorb ammonia excreted by abalone. Degree of supplemental illumination, water volume exchange rate, and abalone body weight all affected maximum stocking densities within the co-culture system. The growth rates of abalone fed dulse grown under all co-culture conditions (range: 112–132 μm shell length d −1) compared favorably with that of abalone fed on other algal and artificial diets. Both duration of supplemental illumination and water volume exchange rate affected abalone growth. Overall, the co-culture of dulse and abalone provides the farmer with a reliable supply of nutritious abalone food while ensuring high water quality through uptake of excreted ammonia by the dulse.

The nutritional value of Palmaria mollis cultured under different light intensities and water exchange rates for juvenile red abalone Haliotis rufescens

A growth experiment with juvenile red abalone was conducted to determine whether the nutritional quality of red macroalga dulse ( Palmaria mollis) was dependent on dulse culture conditions. Dulse culture conditions differed by seawater volume exchange rate (1, 6, or 35 d −1) and supplemental illumination (0 or 24 h d −1), creating a variety of dulse morphologies, biochemical compositions, and palatabilities for red abalone. The results of this study agreed with those of previous studies, showing dulse to be of high nutritional quality for abalone, with a relatively high protein content when compared with other macroalgae. Specific growth rates (SGR) of abalone fed on all dulse diets were higher than those of abalone fed on kelp ( Nereocystis luetkeana). In general, abalone grew faster on dulse cultured with supplemental illumination. Protein content of dulse (10.85–18.22% dry wt.), however, was directly dependent on seawater volume exchange per day, with highest protein levels observed in dulse cultured with 35 volume exchanges d −1. We suggest that other variables apart from biochemical composition, such as epiphytic diatoms and morphological differences, contributed to the higher growth rates of abalone fed on light-supplemented diets.

Effect of Heated and Unheated Fish Silage as a Protein Source in Diets for Abalone Haliotis fulgens

AbstractBoth unheated (US) and heated (HS) fish silage were evaluated as sole dietary protein sources in an artificial diet for the culture of juvenile abalone Haliotis fulgens. The fish silage was heated to reduce the level of hydrolysis and thereby increase the availability of nutrients. After 140 d of culture, growth rates of abalone fed the US‐ and HS‐containing diets were 16.4 and 19.8 μm/d and were not significantly different despite greater leaching of protein and carbohydrate in the US‐containing diet. Growth rates achieved with the US‐ and HS‐containing diets were significantly lower than that achieved by feeding a commercially available diet used as a reference diet. Abalone that were fed the US‐ and HS‐containing diets were then switched to a diet in which two‐thirds of the total amount of silage was replaced with fishmeal. At the termination of the experiment, day 217, the abalone originally fed the US and HS diets had composite growth rates of 24.3 and 23.5 μm/d, while abalone that continued to be fed the commercial diet had a growth rate of 18.6 μm/d. Stability of the dry matter of the diets was not related to the level of protein leaching. Fish meal out performs fish silage as a dietary protein source for abalone. However, growth rates achieved still fall short of that needed to achieve a market size product within a 2‐yr period of growth.

Can crystalline arginine be used to quantify the arginine requirement of abalone?

The feasibility of using crystalline arginine in semi-purified diets to determine the quantitative arginine requirement of abalone was investigated. To this end, the assimilation efficiency of labelled [U- 14C]arginine incorporated into a formulated feed by the South African abalone, Haliotis midae, was studied. In addition, the effect of crystalline arginine supplementation on abalone growth rate was determined. The retention of [U- 14C]arginine by abalone was very low, being 11% of ingested [U- 14C]arginine. Diets supplemented with graded levels of crystalline arginine failed to produce any improvement in the growth rate of abalone. Possible reasons for the failure of crystalline arginine to boost abalone growth are discussed.

Contribution of diatoms as food sources for post-larval abalone Haliotis discus hannai on a crustose coralline alga

Survival and growth rates of post-larval abalone Haliotis discus hannai reared on a crustose (non-geniculate) coralline alga (CCA) Lithophyllum yessoense with diatoms (CCA + diatoms) and without diatoms (CCA − diatoms) were compared in the laboratory in order to determine the contribution of diatoms on CCA as food sources for post-larvae and the dietary value of CCA themselves. Experiments were performed for 5 weeks with two groups of different developmental stage, newly metamorphosed stage (younger postlarvae) and over 1 mm stage (older post-larvae). Both stages of post-larvae reared on CCA + diatoms grew well (53.4 ± 2.4 μm/day; mean ± SE and 85.0 ± 4.0 μm/day; mean ± SE, respectively). Younger post-larvae grew to over 2 mm in 5 weeks, and older ones reached over 4 mm in 5 weeks. There was no difference in shell length of younger post-larvae reared on CCA + diatom and CCA − diatom at the week 1. However, the mean growth rate of abalone on CCA − diatoms from the second to fifth week (24.4 ± 1.9 μm/day; mean ± SE) was significantly lower than that of individuals on CCA + diatoms and the younger post-larvae on CCA − diatoms reached only 1 mm shell length in 5 weeks. The older post-larvae also did not grow well (27.8 ± 3.3 μm/day; mean± SE) on CCA − diatoms and did not reach 3 mm by the end of the experiment. On CCA + diatoms, 74.6 ± 2.0 % (mean ± SE) of the younger post-larvae survived for the 5 weeks experiment. In contrast, the survival rate of the younger post-larvae reared on CCA − diatoms decreased rapidly until the second week, and 25.0 ± 12.6% (mean ± SE) of the individuals survived by the fifth week. The results of this study indicate that diatoms are essential for the rapid growth of post-larval abalone on the CCA. It is considered that the CCA L. yessoense itself is not principal food source for post-larval H. discus hannai from approximately 500 11m to at least 3 mm shell length.

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

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.

Dietary value of benthic diatoms for the growth of post-larval abalone Haliotis discus hannai

The feeding behaviour and the growth of post-larval abalone (1–2 mm in shell length) Haliotis discus hannai fed on nine species of benthic diatom were examined in the laboratory. Digestion efficiencies of abalone fed on the nine diatom species were also measured. All abalone showed active feeding behaviour and diatom cells were observed in their stomachs. However, the growth rates of abalone fed on four diatom species, which were readily digested, were higher than those of abalone fed on the other five species of diatom. The cell walls of the former four diatom species were easily broken open when they were grazed by abalone because of their high adhesive strength (three species), or due to the weakly silicified cell walls (one species with a low adhesive strength). The other five species, whose adhesive strengths are low, were easily ingested by abalone without any deformation of the cell walls and the majority of them were excreted whole and still alive. It is considered that post-larval abalone cannot digest diatom cell contents in their alimentary canal without first rupturing the cell wall with the radula. It is thought that the post-larvae which ingested the latter five diatom species could not readily absorb the diatom cell contents as the cell wall was intact and thus their growth rates were low.

Digestive efficiency of the Australian abalone Haliotis rubra in relation to growth and feed preference

The digestibilities of dry and organic matter, energy and nitrogen were determined for Haliotis rubra feeding on a range of monospecific algal diets. These digestibilities, in conjunction with total intakes, were used to estimate the daily intakes of nitrogen and energy of abalone feeding on those algal species used by Fleming (1995). These were then used to explain the growth rates, intakes and chemosensory preferences of abalone in that study. The chemosensory preferences of abalone were strongly related to the digestible nitrogen content of the algae and to a slightly lesser extent the nitrogen content of the algae, indicating the important role nitrogen plays in setting preferences in this abalone. The intakes of digestible nitrogen were significantly related to the growth rates of abalone, suggesting that nitrogen is a limiting nutrient to abalone growth. Thus, H. rubra selects those foods which maximise the intake of nitrogen and result in maximum growth rates. Energy does not appear to play a major role in setting abalone preference as the digestible energy contents of algae in this study (and in general) are similar and did not correlate with preference. The digestible nitrogen content was lowest in the 3 brown algae tested and digestibility was related to the polyphenolic content of the brown algae. This suggests that the low growth of H. rubra on these species results from the action of polyphenolic compounds, reducing nitrogen digestibility.