David Scott Francis

Hybrid abalone (Haliotis laevigata x H. rubra) perform well when fed plant-based feed ingredients. However, the extent to which they are fully digested and contribute to growth in hybrid abalone remain to be examined. Exogenous enzymes are commonly employed to improve the value of plant-based feeds in other species. Therefore, single and complexed multi-enzyme supplements were used to examine growth indices, feed utilisation and digestive capacity in two simultaneous trials. The complex exogenous enzymes were included at 400 ppm (CE 400 ppm) and 800 ppm (CE 800 ppm) while single application were applied at 320 ppm (IE Protease), 80 ppm (IE Phytase) and 100 ppm (IE Xylanase). Initially, juvenile hybrid abalone weighing 9.03 ± 0.03 g were stocked into triplicate tanks, receiving flow-through seawater and fed for a total of 108 days. The results showed that the complexed enzymes improved the apparent digestibility of the diets overall, however, this was not translated into improved growth indices. The feed intake was reduced in the CE diet fed abalone, negatively affecting the growth response. For the IE fed abalone, there were subtle differences observed for apparent digestibility, however, none were significantly improved compared to the control. The exception to this was improved carbohydrate digestibility in the IE Phytase fed abalone, which led to an increase in soft tissue carbohydrate composition. There were no significant differences in any growth indices or feed utilisation parameters. α-Amylase activity in the digestive gland was reduced in all treatments compared to the control. Based on these results, and using the formulation described herein, selecting exogenous enzymes for hybrid abalone may provide only limited benefits as the growth performance response appears to be driven mostly by feed intake. If the palatability of diets is addressed, and therefore improved feed intake, then there is potential for improved weight gain based on the apparent digestion values.

Hybrid abalone (Haliotis laevigata x H. rubra) perform well when fed plant-based feed ingredients. However, the extent to which they are fully digested and contribute to growth in hybrid abalone remain to be examined. Exogenous enzymes are commonly employed to improve the value of plant-based feeds in other species. Therefore, single and complexed multi-enzyme supplements were used to examine growth indices, feed utilisation and digestive capacity in two simultaneous trials. The complex exogenous enzymes were included at 400 ppm (CE 400 ppm) and 800 ppm (CE 800 ppm) while single application were applied at 320 ppm (IE Protease), 80 ppm (IE Phytase) and 100 ppm (IE Xylanase). Initially, juvenile hybrid abalone weighing 9.03 ± 0.03 g were stocked into triplicate tanks, receiving flow-through seawater and fed for a total of 108 days. The results showed that the complexed enzymes improved the apparent digestibility of the diets overall, however, this was not translated into improved growth indices. The feed intake was reduced in the CE diet fed abalone, negatively affecting the growth response. For the IE fed abalone, there were subtle differences observed for apparent digestibility, however, none were significantly improved compared to the control. The exception to this was improved carbohydrate digestibility in the IE Phytase fed abalone, which led to an increase in soft tissue carbohydrate composition. There were no significant differences in any growth indices or feed utilisation parameters. α-Amylase activity in the digestive gland was reduced in all treatments compared to the control. Based on these results, and using the formulation described herein, selecting exogenous enzymes for hybrid abalone may provide only limited benefits as the growth performance response appears to be driven mostly by feed intake. If the palatability of diets is addressed, and therefore improved feed intake, then there is potential for improved weight gain based on the apparent digestion values.

Crude protein content of food and feed products are estimated using total nitrogen content and the universal factor (UF) 6.25. UF is unreliable for many food and feed matrices that contain substantial non-protein nitrogen (NPN). Species or matrix specific conversion factors (CF) derived from aminoacid profiles provide reliable and accurate estimates of true protein. Here we describe a standardized workflow and open web application for calculating Kjeldahl nitrogen-to-protein conversion factors from total nitrogen and proteinogenic aminoacid data. The method converts user-supplied aminoacid values into anhydrous aminoacid residues (g per 100 g dry weight), divides by total Kjeldahl nitrogen (% dry weight), and returns a species-specific CF for use in the equation: Crude protein (%) = Total Kjeldahl nitrogen (%) × CF. The tool supports six aminoacid reporting units, validates required inputs, compares results with the default factor 6.25, exports citable records, and maintains a searchable database of published conversion factors. Validation against independent literature datasets for a red seaweed (Cryptonemia seminervis), a brown seaweed (Padina gymnospora), and mealworm larvae (Tenebrio molitor) showed exact agreement with published factors (3.75, 5.72, and 5.41, respectively). Using 6.25 instead of the species-specific factors overestimated crude protein by 67%, 9%, and 15%, respectively.

Associations with fish can benefit corals by increasing growth and stress tolerance. To investigate microbial and nutritional responses of corals to fish associations in the context of enhancing coral aquaculture outcomes, Pocillopora verrucosa were cultured for 3 months with different combinations of live feeds and schools of juvenile Chromis viridis damselfish. The combined live feeds and fish treatment resulted in a bacterial community most similar to wild P. verrucosa , dominated by Endozoicomonas‐ affiliated taxa. Protein content was enhanced in corals with access to live feeds and/or dissolved fish wastes compared to unfed controls. Total lipid concentrations were elevated in captive corals with access to dissolved fish wastes and at moderate levels in those supplied live feeds, likely due to the activity of corals' symbionts and deposition of derived lipids from live feeds, respectively. However, all captive corals demonstrated a significant reduction in storage lipid concentration compared to samples from the wild. Fatty acid analysis indicated these shifts were likely the result of higher light levels in the field supporting Symbiodiniaceae photosynthesis and potentially feeding on wild zooplankton. Co‐culturing captive corals with fish and providing appropriate live feeds may therefore offer an effective approach to improve coral nutrition, health and microbiome stability.

Rearing variables, such as water temperature and dietary composition, can significantly affect gut transit time (GTT) in cultured Atlantic salmon ( Salmo salar ). These influences can accelerate the transit of digesta, leading to reduced nutrient digestibility and uptake, whilst impacting feed intake, appetite and gut evacuation, which collectively may result in inefficient feed utilisation in commercial aquaculture. To address these issues, manipulating the physical properties of the diet, specifically pellet and raw material particle size, may present a solution via the modulation of the GTT in fish. This study aimed to evaluate the GTT of 360 pre‐smolt Atlantic salmon (120.58 ± 0.25 g) fed one of six dietary treatments varying in raw material particle size (fine: 0–250 μm, medium: 250–500 μm or coarse: 500 μm–1000 μm) and subsequent pellet size (3 mm or 5 mm) using a factorial design. GTT was quantified by assessing the relative distribution of an inert feed marker (ballotini® beads), incorporated in the feed, in three defined digestive tract regions: the stomach (ST), mid‐intestine (MI) and distal intestine (DI). It was found that the larger pellet size resulted in faster transit of digesta, but the relationship between raw material particle size (fine, medium or coarse) and transit rate was highly variable. However, the time taken for 50% evacuation of the digesta present in the GI tract is modulated by both pellet and raw material particle size. The insights gained from this research could guide the development of commercial diets designed to mitigate the negative impacts of an accelerated gut transit. Consequently, this approach has the potential to enhance feed efficiency from both nutritional and economic perspectives and reduce the environmental impact caused by excessive nitrogenous waste production in aquaculture.

Some coral species in natural reef systems derive benefits from fish which live in close association with them. This study investigates the benefits of incorporating fish in ex situ coral culture to enhance coral physiological performance. Corals that typically have fish associations ( Acropora kenti and Pocillopora verrucosa ) and those that do not ( Porites lutea and Platygyra daedalea ) were grown in aquaria under different fish‐associated treatments for 3 months. Physiological performance of the corals, including growth, protein content, symbiont density and photosynthetic efficiency were assessed in the different treatments where corals were (1) kept with a school of Chromis viridis fed a pelleted diet, (2) supplied filtered water from a tank housing C. viridis , (3) fed live feeds whilst maintained with C. viridis , (4) supplied only with live feeds, (5) supplied with a pelleted fish diet without C. viridis and (6) not supplied feeds and without C. viridis . Whilst the responses of the corals varied between species, generally, exposure to fish or fish‐water increased the protein and/or symbiont density within coral tissue. A. kenti and P. lutea , which derive a higher proportion of their energy requirement from autotrophy, displayed improved growth in the fish treatments, whilst the more heterotrophic P. verrucosa grew fastest when supplied with live feeds. The more heterotrophic, slow‐growing P. daedalea did not show significant improvements in growth under any of the treatments, and there were no major differences in photosynthetic efficiency between treatments in any of the corals. These results indicate that incorporating fish into coral culture could provide an accessible source of nitrogen and phosphorous enrichment via the dissolved portion of the fish’s wastes and, in turn, enhance the growth of corals more reliant on autotrophy, like Acroporids. The results point to potential efficiency gains for coral husbandry practices, with the aim of satisfying the growing demands of reef restoration and ornamental aquaculture.

There is growing interest in the use of single cell proteins (SCPs) derived from methanotrophic bacteria for inclusion in aquafeed to reduce reliance on other, potentially less sustainable proteins. This two‐part experiment aimed to investigate first (i) the dose effect of replacing soy protein concentrate with SCP in Australian hybrid abalone diets ( Haliotis laevigata Haliotis rubra ) and second, (ii) the potential for improved palatability of the SCP by using commercially produced liquid protein hydrolysate (PH). This was assessed in a 2 × 2 factorial experimental design. The diets were formulated to be iso‐proteic (~40% crude protein as fed) and iso‐energetic (~18 MJ kg ⁻¹ as fed). The diets (SCP 0%, SCP 5%, SCP 10%, SCP 20%, SCP 0% + PH, and SCP 20% + PH) were fed to the abalone (~9.25 g initial weight) once daily in the evening for 94 days to apparent satiation. The growth performance and feed utilization of abalone fed with up to 10% SCP was comparable to the control; however, there was a significant reduction in most parameters at the highest inclusion of 20%. In the second experiment, there was a decline in measured protein and energy retention in the abalone fed 20% SCP, with a concomitantly lower apparent biological value. Positively, there were significant improvements in the apparent digestibility of the diet at the 20% SCP inclusion. There was no significant impact of using the PH on growth performance or feed intake. No effects were observed on the digestive enzyme activity ( α ‐amylase, lipase, and trypsin) examined among the treatments. Considering these results collectively, the maximum recommended inclusion of methanotrophic SCP meal should be 10% for hybrid abalone. Reasons for the decline in performance at the highest inclusion may be related to palatability; however, this remains to be fully confirmed.