Geoff L. Allan

Replacement of fish meal in diets for Australian silver perch, Bidyanus bidyanus: I. Digestibility of alternative ingredients

Apparent digestibility coefficients (ADCs) for dry matter, nitrogen, energy and individual amino acids for 29 commonly used feed ingredients were determined for silver perch, a native Australian freshwater species currently being cultured in Australia, Taiwan and China. ADCs were determined using faeces collected following settlement. Results from 11 experiments are reported. Each experiment included a reference diet and test diets, which were composed of 69.3% reference diet, 29.7% test ingredient and 1% chromic oxide (inert indicator). Ingredients tested included Australian, Danish and Peruvian fish meals, blood meal, meat and bone meals from beef and lamb, poultry meal, feather meal, soybean and canola meals (both expeller and solvent extracted for each), full fat soybeans, peanut meal, cottonseed meal, linola, two species of lupins, field peas, faba beans, chick peas, vetch, cow peas, wheat gluten, corn gluten meal, two cultivars of wheat, millrun and sorghum. ADCs for dry matter, energy and nitrogen were highest for fish meal, although several other ingredients, including some animal meals and gluten from wheat and corn, had similar ADCs for dry matter and energy. Digestible protein from these ingredients was in the range 52-86% compared with 63-69% for fish meals. Silver perch were capable of digesting protein very effectively in almost all ingredients tested. Amino acid availability reflected nitrogen digestibility except for Peruvian fish meal and the two meat and bone meals, for which the availability of some amino acids was lower, possibly indicating protein damage during processing. Oilseeds and legumes also tended to have lower ADCs for some amino acids (e.g., sulphur amino acids) than for other amino acids. Differences in ADCs for nitrogen and individual amino acids indicate the need for individual amino acid availability data. The data provided a useful starting point for least-cost formulation of diets for silver perch.

Replacement of fish meal in diets for Australian silver perch, Bidyanus bidyanus: IV. Effects of dehulling and protein concentration on digestibility of grain legumes

Three digestibility experiments were conducted using juvenile silver perch. The first factorial experiment evaluated four ingredients; field peas (Pisum sativum), faba beans (Vicia faba), chick peas (Cicer arietinum) and vetch (Vicia sativa) with and without hulls. The second and third experiments determined digestibility of field pea, faba bean and lupin protein concentrates. Apparent digestibility coefficients (ADCs) were determined using indirect procedures. Test diets comprised 29.7% of the test ingredient, 69.3% of a practical reference diet and 1.0% chromic oxide as the inert indicator. Faeces were collected from fish by passive settlement techniques. Two-factor ANOVA of the data from the first experiment revealed a significant interaction between ingredient type and the presence/absence of hulls for dry matter, protein and energy digestibility. Dry matter and energy ADCs for whole grains ranged from 43–58% and 51–59%, respectively. Dehulling significantly improved the dry matter and energy digestibility of all grains except faba beans. Dehulled vetch had the highest dry matter (81%) and energy (81%) digestibility of all grains, but diets containing 30% vetch were poorly accepted by silver perch. Protein digestibility for all legumes was high, ranging from 71% to 91% for whole grains and 80–97% for dehulled grains. Protein digestibility was significantly improved by dehulling field peas, faba beans and vetch, but dehulling did not affect protein digestibility of chick peas. Dry matter and energy ADCs for protein concentrates were much higher than either ADCs for whole or dehulled grains. Protein digestibility was highest for the field pea concentrate (97%), but protein ADCs for concentrates of faba beans and lupins were of a similar value to that of their respective dehulled grains. Silver perch have demonstrated they can efficiently digest the protein from the dehulled and refined legumes evaluated in this study. Further, both dry matter and energy digestibility of most grains was dramatically improved after dehulling or protein concentration, indicating processes such as these are highly desirable for legumes prior to their inclusion in diets for silver perch. The cost effectiveness of using protein concentrates in aquaculture diets requires further evaluation. Of the grain legumes investigated in this study, dehulled field peas appear the most promising for juvenile silver perch.

Accumulation and clearance of the anaesthetics clove oil and AQUI-S™ from the edible tissue of silver perch (Bidyanus bidyanus)

The accumulation and clearance of the main component of the fish anaesthetic clove oil (eugenol), from the edible tissue of silver perch (Bidyanus bidyanus) were examined. Fish were sampled from a commercial silver perch farm to determine the efficiency of commonly employed purging practices in clearing fish treated with this product. After initial exposure to clove oil at harvest, fish were purged for 48 h. This proved sufficient to clear eugenol to below detectable levels. However, following an additional application of clove oil for transport and subsequent purging for 1 week, fish had a mean of 0.32 mg kg−1 of eugenol in their tissues. This indicates that repeated doses of clove oil may lead to fish having a decreased capacity to completely clear their tissue of residue. The effect of temperature and treatment upon the accumulation and clearance of eugenol (or iso-eugenol) was also examined. Fish were exposed to 50 mg L−1 clove oil, 15 mg L−1 clove oil, 15 mg L−1 AQUI-S™, or to no anaesthetic, in water that was either heated or at ambient temperature. At the high dose of clove oil, more eugenol was accumulated in heated water but at the low dose, temperature did not influence the amount of eugenol accumulated. Fish treated with AQUI-S™ accumulated more iso-eugenol at ambient temperature than they did in the heated water. Silver perch were generally able to clear their flesh of residue more rapidly at the higher temperature, although regardless of treatment, residue was cleared to below detectable levels in all fish after 48 h.

Acute and chronic toxicity of ammonia to juvenile Metapenaeus macleayi and Penaeus monodon and the influence of low dissolved-oxygen levels

Abstract Acute toxicity of ammonia was estimated as 96-h LC 50 values. For juvenile school prawns, Metapenaeus macleayi , and leader prawns, Penaeus monodon , these were 1.39 and 1.69 mg un-ionised ammonia, NH 3 -N/l (26.3 and 37.4 mg total ammonia-N/l), respectively. Reduced dissolved-oxygen (DO) levels significantly ( P P. monodon . Ninety percent of prawns held for 96 h at a DO level of 2.3 mg/l and an ammonia concentration of 1.60 mg NH 3 -N/l (33.5 mg total ammonia-N/l) died, whereas only 33.3% died at a DO level of 5.7 mg/l and a similar ammonia concentration of 1.63 mg NH 3 -N/l (33.9 mg total ammonia-N/l). The “maximum acceptable” level of ammonia was defined as that which reduced growth by 5% over 3 weeks. For M. macleayi and P. monodon these levels were 0.35 and 0.21 mg NH 3 -N/l (7.7 and 4.1 mg total ammonia-N/l), respectively.

Survival and growth of Australian snapper, Pagrus auratus, in saline groundwater from inland New South Wales, Australia

Australia has extensive resources of inland saline groundwater, which may be suitable for culture of marine fish. This study assessed the suitability of saline groundwater, which was pumped from a shallow aquifer into an evaporation pond near Wakool in western New South Wales, for growth and survival of juvenile snapper, Pagrus auratus. Five experiments were conducted. The first showed that snapper (31 g) did not commence feeding, lost equilibrium of buoyancy and became moribund within 3 days after transfer from coastal seawater (diluted to 19‰ with rainwater) to saline groundwater (19‰). Potassium concentration of diluted coastal seawater and groundwater (both 19.6‰) was 203 and 9.2 mg l−1, respectively, while the concentration of most other major ions was similar in water from both sources. In the second experiment, groundwater of 21‰ salinity was fortified with potassium (as KCl) to provide 25%, 50% or 100% of the concentration of potassium found in coastal seawater of 21‰ salinity. Survival and feeding and swimming behaviour of snapper (1.5 g) held in tanks for 8 days were the same in 50% and 100% potassium-fortified treatments as in coastal seawater controls. However, snapper held in groundwater fortified with only 25% potassium, or raw saline groundwater became moribund after 4 and 2 days, respectively. During the third 42-day experiment, growth, survival and food conversion of juvenile snapper (4.0 g) were the same in diluted coastal seawater (20‰) and groundwater (20‰) provided the level of potassium in the groundwater was increased to within 60–100% of the concentration in coastal seawater. During the fourth experiment, juvenile snapper were acclimatised to raw saline groundwater by transferring fish from fortified groundwater with initial potassium levels of 100% of that in coastal seawater, to groundwater with 10% lower potassium levels every 3.5 days or 20% lower levels every 7 days. A further treatment where snapper were transferred from groundwater fortified initially with potassium levels of 60% of coastal seawater, to groundwater with 20% lower potassium levels every 3.5 days was included. When potassium was reduced to 20% of the concentration in coastal seawater, in all treatments, fish became moribund. Results from the fifth experiment, where groundwater was fortified with either KCl or NaCl at equivalent chloride levels, confirmed that potassium and not chloride ions were responsible for improvement in groundwater. Our results demonstrate that saline groundwater from Wakool, fortified with KCl is a suitable medium for growing snapper juveniles in tanks.

Nutrient digestibility for juvenile silver perch Bidyanus bidyanus: development of methods

Abstract Three experiments were undertaken to develop methods for determining digestible energy, dry matter and protein of diets and feed ingredients for juveniles (5–15 g/fish) of the Australian freshwater fish, silver perch. The first experiment compared stripping, dissection and settlement as methods of collecting faeces. Stripping was not a suitable method for collecting digesta from juvenile silver perch ≤10 g/fish; insufficient sample was obtained and regurgitation of food contaminated samples. Digestible dry matter calculated using digesta collected by dissection were lower than values using faeces collected following settlement. Values using digesta extracted from the posterior portion of the intestinal tract were higher than those using digesta from the anterior portion. In the second experiment, separate digestibility coefficients (DC) were calculated using faeces collected by settlement every 2 h (up to 18 h) after tanks were cleaned and these were compared with DCs calculated using faeces collected 6, 12 or 18 h after tanks were cleaned. Digestible energy and digestible dry matter increased with time. Digestible dry matter was similar when calculated using faeces collected over 12 or 18 h and greater than for faeces collected over 2 or 6 h. Digestible energy and digestible dry matter calculated using faeces collected every 2 h and averaged to give a value for 6, 12 or 18 h were similar to values calculated using faeces collected over 6, 12 or 18 h periods. This indicated that leaching did not affect digestible coefficients after faeces had settled. The third experiment validated the assumption that DCs for juvenile silver perch for different feed ingredients are additive. The sum of DCs calculated separately for individual ingredients was similar to that calculated for a diet composed of those ingredients. These results demonstrate that collection of faeces by settlement over 18 h is a suitable method for determining digestibility in juvenile silver perch.

Lethal levels of low dissolved oxygen and effects of short-term oxygen stress on subsequent growth of juvenile Penaeus monodon

Abstract The lethal level (96 h LC50) of dissolved oxygen (DO) for juvenile Penaeus monodon was estimated to be 0.9 mg O2 l−1 (95% confidence limits: 0.8, 1.0 mg O2 l−1). Other replicate groups of P. monodon were subjected to short-term, severe DO stress and then grown under conditions approaching DO saturation. The aim was to simulate the type of event which can occur in ponds when emergency aeration successfully raises DO after an oxygen crisis. Neither the duration (4, 8 or 12 h), nor the level (0.5-0.6 or 1.0–1.1 mg O2 l−1) of the DO stress significantly (P>0.05) reduced subsequent growth or food conversion efficiency at favourable DO levels over 21 days. Prawn pond managers should not need to reduce feeding levels or consider premature harvest after a single, short-term DO crisis when mass mortality is avoided. This is provided that other water quality variables do not reach critical levels during the crisis.

Effect of photoperiod on growth and survival of snapper Pagrus auratus larvae

Abstract Experiments were done in 100-l recirculation tanks to determine the effects of photoperiod on (1) first-feeding and (2) post-swimbladder inflated snapper, Pagrus auratus, larvae. In Experiment 1, feeding onset, growth, initial swimbladder inflation, and tail flexion were assessed at five photoperiod treatments (0L:24D, 6L:18D, 12L:12D, 18L:6D, and 24L:0D) in larvae from 3 to 15 days after hatching (dah). Growth and development of first-feeding larvae increased with increasing photoperiod duration in the 12L:12D to 24L:0D treatments. Larvae did not start feeding in 0L:24D and onset of feeding was delayed by up to 3 days in 6L:18D. All larvae held in 0L:24D and 6L:18D died within 6 or 9 dah, respectively. Initial swimbladder inflation was best (80–100%) in an intermediate photoperiod of 12L:12D at 9 dah. By 15 dah, although the percentage of larvae with inflated swimbladders had increased in all treatments, swimbladder inflation in 12L:12D was 1.3 and 2.0 times greater than that of larvae in 18L:6D and 24L:0D, respectively. In the second experiment, growth and survival of snapper after the initial swimbladder inflation period (11–32 dah) were assessed at three photoperiod treatments (12L:12D, 18L:6D, and 24L:0D). Growth was greatest in 18L:6D in which wet weights (16.3±0.5 mg; mean±S.E.) and dry weights (2.8±0.1 mg; mean±S.E.) of larvae were approximately 1.3 and 1.9 times heavier than the larvae held in 24L:0D and 12L:12D, respectively. Survival of snapper larvae to 32 dah was not significantly different between the three photoperiod treatments, but power of the experiment to detect effects on survival was small due to large variability within treatments. Further research is needed to determine optimal photoperiods for the survival of the snapper larvae. Because of the potential for large larval mortality, if initial swimbladder inflation is not achieved, the optimal photoperiod for the period from feeding onset to swimbladder inflation (3–15 dah) was deemed to be 12L:12D, whereas on the basis of growth parameters that were measured (total length, wet and dry weights), 18L:6D was determined to be the optimal photoperiod for the culture of snapper from the post-swimbladder window to metamorphosis (11–32 dah).

Biochemical composition of new yeasts and bacteria evaluated as food for bivalve aquaculture

Abstract The biochemical compositions of seven strains of marine bacteria and six strains of yeast—all isolated from an Australian waterway—were compared with two well-studied yeast strains, Candida utilis and Saccharomyces cerevisiae , to assess their nutritional quality for bivalve aquaculture. Protein was a major constituent of both yeast and bacteria (25–49% dry weight), with lipid a minor component (2.5–9.0%). Carbohydrate in yeast was 21–39% of dry weight, bacteria had 2.5–11%. Ash ranged from 4.7 to 14% dry weight in 11 of the yeast and bacteria strains; the remaining species, all bacteria, had high levels (29–40%). Nucleic acid ranged from 3.3 to 8.4% dry weight in the yeast and bacteria. The amino acid compositions were similar in the strains, and closely matched those of Saccostrea commercialis larvae and spat indicating a high protein quality. Glucose was a major sugar in the polysaccharide of both yeast and bacteria (12–73% of total sugars); mannose was in high concentrations in the yeast (24–65%). Both polyunsaturated fatty acids (PUFAs) 20:5 n − 3 and 22:6 n − 3 were absent in all strains, and thus if the strains are to be used in bivalve aquaculture, they would need to be supplemented with live algae rich in these PUFAs. High levels of good quality protein, however, indicate their potential to provide important nutrients in a mixed diet.

Effects of pH and salinity on survival, growth and osmoregulation in Penaeus monodon Fabricius

Abstract Critical levels of low pH for juvenile Penaeus monodon (4.2–5.5 g average weight), were determined using static bioassays with seawater acidified by using hydrochloric acid ( HCL ). The lethal pH (96 h LC 50 ) was 3.7 (95% confidence limits; 3.4 and 4.1 ) at a salinity of 32‰. The minimum acceptable pH, defined as that pH which reduced growth by 5% over 23 days, was estimated as 5.9 at a salinity of 30p. In comparison to a pH of 7.8, long-term (23 days) exposure to low pH (4.9) at 30‰ salinity also significantly decreased dry matter content of the prawns ( P P P P > 0.05) while the pH × salinity interaction was significant ( P P P P > 0.05). The estimation of lethal and minimum acceptable low pH values should assist prawn farmers with the management of acid ponds.