Brett Glencross

Influence of oligosaccharides on the digestibility of lupin meals when fed to rainbow trout, Oncorhynchus mykiss

We examined the influence of the oligosaccharide component of a lupin (Lupinus angustifolius) meal when fed to rainbow trout. Two strategies for examining the influence of oligosaccharides were undertaken, including the use of an exogenous enzyme supplement of α-galactosidase to degrade the oligosaccharides and ethanol extraction processing to remove the oligosaccharides. Controls for both processing and degradation of the galactosides were also included in the study. The test treatments were fed to the fish as 30% of their diet and were compared against a reference diet using standard diet-dilution digestibility techniques. The removal of the ethanol-soluble component of the lupin meal had the greatest influence on its apparent digestibility, with significant effects clearly seen on the digestibility of the nitrogen, organic matter and nitrogen-free extractive (NFE) components. Addition of exogenous α-galactosidase to the lupin meal produced a significant difference in the digestibility of nitrogen and numerical improvements in the values of most nutrient parameters. Comparison of the digestibilities of the enzyme-supplemented lupin meal, the galactose-supplemented extracted lupin meal and the original lupin meal treatments indicated that rainbow trout can absorb the monosaccharides produced from the degradation of α-galactosides. This improvement was further validated by examining the influence of the ethanol extraction process, which showed that it is the removal of the ethanol-soluble components, most likely oligosaccharides, that is the contributing factor. These findings indicate that further processing of lupin meals to remove their oligosaccharide fraction would have beneficial nutritional implications for fish.

The dietary protein and lipid requirements of post-puerulus western rock lobster, Panulirus cygnus

Abstract The dietary requirements of post-puerulus western rock lobster for protein and lipid (fat) were examined in a 6-week, pair-fed feeding study. Incremented dietary amounts of protein (30%, 35%, 40%, 45%, 50% and 55%) at each of two dietary fat levels (6% and 10%) were examined. An additional diet of fresh mussels ( Mytilus edulis ) was included as a reference. At the end of the 6-week growth experiment, growth of the rock lobsters was better when protein levels were greater than 50% of the diet. Growth of rock lobsters was also significantly greater in diets with the lower fat levels. The growth of the animals fed the reference diet was significantly superior to all of the experimental diets. Survival of animals in all treatments was equal to or greater than 75%. Though there were some significant differences in survival among treatments, this was not consistent with any relationship between either protein or fat content of the diets. The number of moulting events observed in each of the test treatments was significantly lower than that observed by the mussel-fed animals. This was consistent with what was observed with the level of growth difference among the test treatments and the mussel-fed treatment. There were no significant differences in the number of moulting events among any of the protein-lipid level treatments. There were no significant differences among the test treatments with feed intake on a proportion of body weight basis. This was in accordance with the pair-feeding protocol of this study. Feed conversion by the lobsters in each of the test treatments was in accordance with what was observed in their corresponding growth responses. Diets containing 6% fat and either 50% or 55% protein had significantly lower FCR values than all other test diets (2.7:1 and 2.5:1, respectively). The diet that had 10% fat and 30% protein had the highest FCR (7.6:1) and was significantly higher than all other diets. There were no other significant differences in feed conversion among the test treatments. The results of this study support that post-puerulus Panulirus cygnus have a very high dietary protein requirement and a poor capacity to utilise dietary lipid. It should be noted though that the relative growth of the post-puerulus P. cygnus fed the pelleted diets was considerably lower than of those fed the reference diet of fresh mussels. Accordingly, optimal diets derived from this study should be based on fat levels of about 6% and protein levels equal to or exceeding 55%.

Readily Available Sources of Long-Chain Omega-3 Oils: Is Farmed Australian Seafood a Better Source of the Good Oil than Wild-Caught Seafood?

Seafood consumption enhances intake of omega-3 long-chain (≥C20) polyunsaturated fatty acids (termed LC omega-3 oils). Humans biosynthesize only small amounts of LC-omega-3, so they are considered semi-essential nutrients in our diet. Concern has been raised that farmed fish now contain lower LC omega-3 content than wild-harvested seafood due to the use of oil blending in diets fed to farmed fish. However, we observed that two major Australian farmed finfish species, Atlantic salmon (Salmo salar) and barramundi (Lates calcifer), have higher oil and LC omega-3 content than the same or other species from the wild, and remain an excellent means to achieve substantial intake of LC omega-3 oils. Notwithstanding, LC omega-3 oil content has decreased in these two farmed species, due largely to replacing dietary fish oil with poultry oil. For Atlantic salmon, LC omega-3 content decreased ~30%–50% between 2002 and 2013, and the omega-3/omega-6 ratio also decreased (>5:1 to <1:1). Australian consumers increasingly seek their LC omega-3 from supplements, therefore a range of supplement products were compared. The development and future application of oilseeds containing LC omega-3 oils and their incorporation in aquafeeds would allow these health-benefitting oils to be maximized in farmed Australian seafood. Such advances can assist with preventative health care, fisheries management, aquaculture nutrition, an innovative feed/food industry and ultimately towards improved consumer health.

Evaluation of the variability in chemical composition and digestibility of different lupin (Lupinus angustifolius) kernel meals when fed to rainbow trout (Oncorhynchus mykiss)

Abstract The study examined the influence of variability in the chemical composition of lupin ( Lupinus angustifolius ) kernel meals on their digestibility when fed to rainbow trout. A range of lupin kernel meals were included into separate diets fed to rainbow trout and the feces collected by stripping. Comparison of the composition of feed and feces was undertaken to assess the extent of nutrient and energy digestibility. There was a strong correlation between protein content of a lupin kernel meal and the digestibility of that protein. Notably, the strongest correlation was that between kernel meal protein content and nitrogen digestibility ( y =0.001(±0.00007) x −0.473, R 2 =0.981, P =0.0011). The identification of this relationship allowed the calculation of equations to predict the digestible protein content of lupin kernel meals based on their crude protein content ( y =1.202(±0.032) x −149.118, R 2 =0.998, P =0.00004). The strong correlation between kernel meal protein content and its nitrogen digestibility had a direct effect on the relationship with energy digestibility. Notably, the kernel meal protein content had more influence on its energy digestibility ( y =0.002(±0.000314) x −0.274, R 2 =0.927, P =0.0086) than that of the nitrogen digestibility. This is likely to be related to the relatively large contribution that protein makes to the dietary energy content of the lupin kernel meal relative to that of the carbohydrate content. The demonstrated relationship, between lupin kernel meal protein content and its nutritional value, provides a good support for the promotion of grain segregation by protein content and commodity pricing according to protein content. More specifically, this should focus on the value per unit of digestible protein when used as an ingredient for fish diets.

Growing backwards: an inverted role for the shrimp ortholog of vertebrate myostatin and GDF11

SUMMARY Myostatin (MSTN) and growth differentiation factor-11 (GDF11) are closely related proteins involved in muscle cell growth and differentiation as well as neurogenesis of vertebrates. Both MSTN and GDF11 negatively regulate their functions. Invertebrates possess a single ortholog of the MSTN/GDF11 family. In order to understand the role of MSTN/GDF11 in crustaceans, the gene ortholog was identified and characterized in the penaeid shrimp Penaeus monodon. The overall protein sequence and specific functional sites were highly conserved with other members of the MSTN/GDF11 family. Gene transcripts of pmMstn/Gdf11, assessed by real-time PCR, were detected in a variety of tissue types and were actively regulated in muscle across the moult cycle. To assess phenotypic function in shrimp, pmMstn/Gdf11 gene expression was downregulated by tail-muscle injection of sequence-specific double-stranded RNA. Shrimp with reduced levels of pmMstn/Gdf11 transcripts displayed a dramatic slowing in growth rate compared with control groups. Findings from this study place the MSTN/GDF11 gene at the centre of growth regulation in shrimp, but suggest that, compared with higher vertebrates, this gene has an opposite role in invertebrates such as shrimp, where levels of gene expression may positively regulate growth.

Influence of dietary docosahexaenoic acid in combination with other long-chain polyunsaturated fatty acids on expression of biosynthesis genes and phospholipid fatty acid compositions in tissues of post-smolt Atlantic salmon (Salmo salar).

To investigate interactions of dietary LC-PUFA, a dose-response study with a range of docosahexaenoic acid (DHA; 22:6n-3) levels (1 g kg(-1), 5 g kg(-1), 10 g kg(-1), 15 g kg(-1) and 20 g kg(-1)) was performed with post-smolts (111 ± 2.6g; mean ± S.D.) over a nine-week feeding period. Additional diets included 10 g kg(-1) DHA in combination with 10 g kg(-1) of either eicosapentaenoic acid (EPA; 20:5n-3) or arachidonic acid (ARA; 20:4n-6), and a diet containing 5 g kg(-1) each of DHA and EPA. The liver, brain, head kidney and gill were collected at the conclusion of the trial, and lipid and fatty acid compositions were determined as well as expression of genes of LC-PUFA biosynthesis. Total lipid content and class composition were largely unaffected by changes in dietary LC-PUFA. However, phospholipid (PL) fatty acid compositions generally reflected that of the diet, although the response varied between tissues. The liver most strongly reflected diet, followed by the head kidney. In both tissues increasing dietary DHA led to significantly increased DHA in PL and inclusion of EPA or ARA led to higher levels of these fatty acids. The brain showed the most conserved composition and gene expression profile, with increased dietary LC-PUFA resulting in only minor changes in PL fatty acids. Dietary LC-PUFA significantly affected the expression of Δ6 and Δ5 desaturases, Elovl 2, 4 and 5, and SREBPs although this varied between tissues with greatest effects observed in the liver followed by the head kidney, similar to PL fatty acid compositions.

Mechanisms of colour adaptation in the prawn Penaeus monodon

SUMMARY Exposure of prawns to dark- or light-coloured substrates is known to trigger a strong colour adaptation response through expansion or contraction of the colouration structures in the prawn hypodermis. Despite the difference in colour triggered by this adaptive response, total levels of the predominant carotenoid pigment, astaxanthin, are not modified, suggesting that another mechanism is regulating this phenomenon. Astaxanthin binds to a specific protein called crustacyanin (CRCN), and it is the interaction between the quantities of each of these compounds that produces the diverse range of colours seen in crustacean shells. In this study, we investigated the protein changes and genetic regulatory processes that occur in prawn hypodermal tissues during adaptation to black or white substrates. The amount of free astaxanthin was higher in animals adapted to dark substrate compared with those adapted to light substrate, and this difference was matched by a strong elevation of CRCN protein. However, there was no difference in the expression of CRCN genes either across the moult cycle or in response to background substrate colour. These results indicate that exposure to a dark-coloured substrate causes an accumulation of CRCN protein, bound with free astaxanthin, in the prawn hypodermis without modification of CRCN gene expression. On light-coloured substrates, levels of CRCN protein in the hypodermis are reduced, but the carotenoid is retained, undispersed in the hypodermal tissue, in an esterified form. Therefore, the abundance of CRCN protein affects the distribution of pigment in prawn hypodermal tissues, and is a crucial regulator of the colour adaptation response in prawns.

A comparative analysis of the response of the hepatic transcriptome to dietary docosahexaenoic acid in Atlantic salmon (Salmo salar) post-smolts.

BackgroundThe present study aimed to explore the impact of dietary docosahexaenoic acid (DHA) on aspects of the metabolism of Atlantic salmon (Salmo salar). The effects of diets containing increasing levels of DHA (1 g kg−1, 3 g kg−1, 6 g kg−1, 10 g kg−1 and 13 g kg−1) on the liver transcriptome of post-smolt salmon was examined to elucidate patterns of gene expression and responses of specific metabolic pathways. Total RNA was isolated from the liver of individual fish and analyzed using a custom gene expression 44K feature Atlantic salmon oligo-microarray.ResultsThe expression of up to 911 unique annotated genes was significantly affected by dietary DHA inclusion relative to a low DHA reference diet. Analysis of a total of 797 unique genes were found with a significant linear correlation between expression level and dietary DHA. Gene-Set Enrichment Analysis (GSEA) identified a range of pathways that were significantly affected by dietary DHA content.ConclusionsPathways that showed a significant response to dietary DHA level included those for long-chain polyunsaturated fatty acid biosynthesis, fatty acid elongation, steroid biosynthesis, glycan biosynthesis, protein export and protein processing in the endoplasmic reticulum. These findings suggest that in addition to clear roles in influencing lipid metabolic pathways, DHA might also have key functional roles in other pathways distinct from lipid metabolism.

Rapid effects of essential fatty acid deficiency on growth and development parameters and transcription of key fatty acid metabolism genes in juvenile barramundi (Lates calcarifer).

Barramundi (Lates calcarifer), a catadromous teleost of significant and growing commercial importance, are reported to have limited fatty acid bioconversion capability and therefore require preformed long-chain PUFA (LC-PUFA) as dietary essential fatty acid (EFA). In this study, the response of juvenile barramundi (47·0 g/fish initial weight) fed isolipidic and isoenergetic diets with 8·2% added oil was tested. The experimental test diets were either devoid of fish oil (FO), and thus with no n-3 LC-PUFA (FO FREE diet), or with a low inclusion of FO (FO LOW diet). These were compared against a control diet containing only FO (FO CTRL diet) as the added lipid source, over an 8-week period. Interim samples and measurements were taken fortnightly during the trial in order to define the aetiology of the onset and progression of EFA deficiency. After 2 weeks, the fish fed the FO FREE and FO LOW diets had significantly lower live-weights, and after 8 weeks significant differences were detected for all performance parameters. The fish fed the FO FREE diet also had a significantly higher incidence of external abnormalities. The transcription of several genes involved in fatty acid metabolism was affected after 2 weeks of feeding, showing a rapid nutritional regulation. This experiment documents the aetiology of the onset and the progression of EFA deficiency in juvenile barramundi and demonstrates that such deficiencies can be detected within 2 weeks in juvenile fish.

Effect of High Water Temperatures on the Utilisation Efficiencies of Energy and Protein by Juvenile Barramundi, Lates calcarifer

This study was undertaken to define the effects of temperature on the energy and protein partial utilisation efficiencies of juvenile Barramundi. The experiment used a factorial design with four temperatures (25oC, 29oC, 32oC, and 36oC) and three ration levels (low, moderate, satiety) to examine the response of Barramundi to varying digestible energy (DE) and digestible protein (DP) intake. Energy and protein deposition with varying intakes at most temperatures were linear, though aberrations occurred at 36oC relative to the other temperatures. The coefficients of DE utilisation were relatively consistent at 0.56 ± 0.02 (mean ± SEM) between 25oC and 32oC, though at 36oC this declined to 0.42 ± 0.04. Similarly the maintenance DE demand for the fish was relatively constant across the range 25oC to 32 oC (~40 kJ DE/metabolic body weight (MBW)/d), but at 36oC dramatically increased to around 110 kJ DE/MBW/d. The coefficients of DP utilisation were also relatively consistent at 0.51 ± 0.02 between 25oC and 32oC, though at 36oC this declined to 0.28 ± 0.12. Similarly, the maintenance DP demand at 36oC dramatically increased from around 0.5 g DP/PBW/d to 1.5 g DP/PBW/d. These results demonstrate that at high temperatures Barramundi protein demand and utilisation is significantly compromised and this affects their ability to efficiently convert dietary protein to tissue growth.