Settling velocity and total ammonia nitrogen leaching from commercial feed and faecal pellets of gilthead seabream (Sparus aurata L. 1758) and seabass (Dicentrarchus labrax L. 1758)

The physico-chemical characteristics of particulate wastes of Sparus aurata and Dicentrarchus labrax were investigated. Changes in the dimensions, settling velocity and total ammonia nitrogen (TAN) leached from commercial feed pellets were investigated after soaking. Also, the settling velocity and TAN leached from faecal pellets of these fish were assessed at 15 and 25 °C. The settling velocity of feed pellets was influenced positively by pellet weight and negatively by immersion length as a result of changes in pellet dimensions after soaking. The settling velocity of faecal pellets was determined by pellet weight. The experimental design did not allow identification of any consistent effect of water temperature on settling velocity. Total ammonia nitrogen leaching over time from feed and faecal pellets was successfully explained by means of a first-order kinetic equation. For feed pellets, water temperature significantly affected the speed of the process and the time at which the maximum TAN leached was reached, but did not influence the maximum TAN leached. Leaching was related to feed pellet size, and so the smaller the pellet, the higher the leaching. Total ammonia nitrogen leaching from faecal pellets was greater per unit weight than in feed pellets. However, neither water temperature nor fish species influenced TAN leaching from faeces.     

Nutrient leaching from coated crustacean rations

The use of ethyl cellulose as a coating agent to retain water soluble nutrients in pelleted feeds was investigated. When the entire ration pellet was coated, minimal nutrient leaching occurred, even after 6 h. Inclusion of individually coated micronutrients was less effective than total pellet coating for nutrient retention, but did help prevent losses due to leaching.     

Performance of Post-juvenile Rainbow Trout Oncorhynchus mykiss Fed Diets Manufactured by Different Processing Techniques

Four different methods of pelleting—extruded (EXT), steam pelleted (STM), using a Universal Pellet Cooker (UPC), and expanded (EXP)—were performed on subsamples of a single batch of mash to determine the effects on feed pellet characteristics, in vivo feed digestibility, and performance of rainbow trout Oncorhynchus mykiss fed the diets for 16 wk. Results indicated that the STM feed was the most (851 g/L) and UPC feed the least (672 g/L) dense, and that UPC feed had the highest % float (8.3%) and, of the pellets that sank, the fastest sink rate (15.1 cm/sec). While some differences occurred among pelleted diets in loss of dry matter (% dry loss) after incubation in a water bath for up to 10 min, the overall % dry loss was only approximately 1–2%. The method of pelleting did not affect fish weight gain, feed conversion ratio, or specific growth rate. Measurement of the apparent digestibility coefficient of dry matter of the test diets using Cr₂O₃ as the marker ranged from 71–89%. While it appeared that the method of pelleting can affect feed characteristics and the amount of feed offered to the fish, fish performance was not affected.     

Water immersion time reduces the preference of juvenile tropical spiny lobster Panulirus ornatus for pelleted dry feeds and fresh mussel

Development of a pelleted dry feed as an alternative to feeding fresh fishery by‐catch is an environmental priority for tropical spiny lobster aquaculture. Earlier studies have shown the lobster's acceptance of pelleted dry feed diminishes rapidly after immersion in water. In this work, we quantified the rate at which dry matter, total protein, soluble protein and individual and total free amino acids were lost from pieces of green‐lipped mussel Perna canaliculus, a commercially‐extruded Penaeus japonicus (kuruma) shrimp feed (KSF) and four laboratory‐made, fishmeal‐based, pelleted feeds upon immersion for up to 7.5 h. The laboratory‐made feeds contained homogenates of either green‐lipped mussel, polychaete (Marphysa sanguinea), prawn (Metapenaeus bennettae) or squid (Sepioteuthis spp.). After being immersed in water for 0, 2.5 or 5 h, these same feeds were offered as a paired choice with KSF in two preference feeding studies with juvenile Panulirus ornatus lobsters. The loobster's preference for fresh mussel always exceeded that of KSF, irrespective of immersion time. Regression of the proportional intake of test feeds against the relative leach rate of KSF identified soluble protein, glycine and taurine as the principal leachate components having the highest positive correlations with the lobster's feeding preference.     

Manufacturing Different Diet Sizes and Its Effect on Pellet Water Stability and Growth of Three Size Classes of Pacific White Shrimp,Litopenaeus vannamei

Abstract

A feed manufacturing method involving the production of large pellets followed by crumbling to desired diet sizes was used to produce six shrimp diets to determine its effect on growth of three size classes of Pacific white shrimp, Litopenaeus vannamei. The six diets containing 45% protein were 0.7 mm crumble, 1.2 mm crumble, 1.7 mm crumble, 2.2 mm crumble, 2.6 mm crumble, and 3.0 mm pellet. These diets were fed to three size classes of shrimp subjected to a four-week growth trial under indoor laboratory conditions. Stocking density was 12 shrimp/aquarium for size class 1 (1.13iö.01 g), 9 shrimp/aquarium for size class 2 (7.31iö.06 g), and 6 shrimp/aquarium for size class 3 (13.12iö. 10 g). Shrimp were fed three times daily and were evaluated for live weight, growth rate, feed conversion ratio (FCR), and survival. Results for shrimp growth appeared to be affected by diet size and pellet water stability. The effects of diet size, however, were more evident on smaller sized shrimp. Weekly growth rates for class 1 and class 2 shrimp indicated significant responses (P < 0.05) to the effects of diet size, while the class 3 shrimp did not show any significant result. The growth rates for both class 1 and class 2 shrimp were lowest at the smallest diet size (0.7 mm crumble) but differed with respect to highest growth rates. The largest diet (3.0 mm pellets) yielded the highest growth rates for class 1 shrimp, while medium sized feed (2.2 mm crumble) produced the best growth for class 2 shrimp. This could be partly attributed to pellet water stability, which had a direct correlation to diet size (r = 0.97). Smaller diet sizes resulting from crumbling larger pellets tend to have lower water stability. The water stability decreased from 82.5% to 76.3% as the 3.0 mm pellets were reduced to 0.7 mm crumbles. Stress cracks are created during crumbling, and surface area to volume ratio are increased as larger particles are reduced to crumbles. These would make smaller diet particles more susceptible to disintegration and nutrient leaching. For class 3 shrimp, the largest pellets produced the highest growth rate. This high growth value, however, was not significantly different (P > 0.05) from growth results produced by the crumbled feed sizes. This observation suggests that diet sizes ranging from 0.7 mm crumble to 3.0 mm pellet could be used for a 13 g shrimp, although preference would be given to larger pellets due to higher growth performance and better pellet water stability. Results for shrimp live weights were similar to results obtained for weekly growth rates. FCR and survival of all shrimp sizes did not show any significant response from the effects of various diet sizes. However, larger shrimp were less efficient in their diet utilization than smaller shrimp.     

Effect of proteolytic enzyme addition to a practical feed on growth of the Pacific white shrimp, Litopenaeus vannamei (Boone)

Four commercially available proteolytic enzymes active over a wide pH range were assessed as shrimp feed additives. Feeds were formulated to contain 1% of the test enzymes by weight. A feed of the same composition with no enzyme addition served as a control. In vitro feed protein digestibility of the feeds was determined using a modified pepsin digestibility method. In vitro protein digestibility results indicated that commercially available proteases added to a shrimp feed formulation and then hot pelleted/dried did retain enzyme activity. Feeds exhibited low weight losses through leaching (≤ 10.9%) and low or no losses of protein content (≤ 2.7%), indicating that the test feeds were available in their entirety to the shrimp. An 8-week feeding trial using the enzyme-supplemented feeds was conducted to evaluate shrimp growth. Mean shrimp survival was high for all treatments (> 90%). One-way analysis of variance did not detect significant differences (P > 0.05) among feeds in terms of survival, weight gain, specific growth rates and feed–weight gain ratios. Although in vitro digestibility indicated the presence of active enzymes in the feed, the feeding trial revealed that shrimp growth was not enhanced by the inclusion of proteases in these feeds. This study provides sufficient proof to emphasize the importance of in vivo investigations before enzyme-supplemented feeds are used with shrimp.     

Biosecure Shrimp Feeds and Feeding Practices: Guidelines for Future Development

For the purposes of this paper, biosecure shrimp feeds and on‐farm feeding strategies refer to the “feed, whether live, fresh, or formulated, and the management of the feed on the farm, should not be an entry point of potential pathogens to the shrimp and/or to the culture system.” The paper reviews the different feeds commonly used for the production of farmed shrimp and discusses their potential risks from a disease perspective, including the use of live hatchery and nursery feeds, the use of live and/or fresh food organisms for the production of broodstock, and the use of dry formulated shrimp feeds for shrimp growout operations. In addition, the paper discusses the critical role played by feed‐processing techniques for the pasteurization and destruction of pathogens within shrimp feeds and the need for nutritionists to formulate feeds for optimal nutrition and health, and not just for optimal growth. The importance of the development and implementation of good on‐farm feed management practices by farmers is discussed, including the prohibition of the top‐dressing of pelleted feeds on farm by farmers with unapproved feed additives such as antibiotics. Finally, the paper discusses the responsibilities of farmers, feed manufacturers, and traders regarding the development and use of recommended biosecure shrimp feeds and feeding practices.     

An acoustic based approach to evaluate the effect of different diet lengths on feeding behavior of Litopenaeus vannamei

Studying shrimp feeding behavior is challenging and, traditionally, studies have been using direct visual observation or video recordings with image analysis under laboratory conditions. Passive acoustics monitoring (PAM) is a non-invasive approach to study feeding behavior of penaeids, as their mandibles emit clicking sounds during feed ingestion. Considering the wide variation available in shrimp diet lengths, our knowledge is still limited about their effects on feeding behavior. The present study was designed to use acoustics to evaluate the feeding behavior of Litopenaeus vannamei fed different diet lengths. A commercial pelleted diet with similar diameter (2.4 mm) and three different lengths was used as treatments “small” (2.35 mm), “medium” (4.26 mm) and “large” (8.42 mm). Three separate trials were performed with fastened shrimp (20 g), using omnidirectional hydrophones and external audio recorders. Our approach started with the characterization of the click acoustic parameters produced by three shrimps when fed the different diet lengths in anechoic chambers (15 L). We then analyze the number of clicks produced per pellet and duration of the clicking activity when shrimp fed a single pellet in individual tanks (1 L). Finally, the acoustic energy of feeding activity and feed consumption, as well as theirs relationship to predict feed intake was evaluated in aquaria (70 L) with five shrimps. The acoustic parameters of isolated clicks were not affected by the different diet lengths, however, doubling the length of the pellet resulted in doubling the number of clicks emitted during feeding activity. The duration of clicking activity per pellet indicated that small pellets are consumed 2.9 and 4.7 times faster than medium and large pellets, respectively. Furthermore, feeding acoustic energy of small pellets decreased rapidly after feed offer, as their faster consumption probably contributed to shrimps achieved satiety earlier than larger diets. Feed consumption was similar among diets length, but significantly correlated with the feeding acoustic energy emitted by L. vannamei, which is a breakthrough in feeding behavioral research. The results highlight the potential and possibilities of an acoustic approach to estimate feed consumption, as well as an alternative to traditional methods in feeding behavioral studies to improve efficiency of feed management.     

Improvement of the stability of commercial feed pellets for the giant shrimp (Macrobrachium rosenbergii)

Different feed pellets for the giant shrimp, Macrobrachium rosenbergii, were compared with respect to water stability, food conversion ratio and growth rate. Pellet stability was observed under tank conditions with and without animals, and leaching rates were measured. Purina Marine Ration M20 was repelletized with Kelco HV algin binder at 0.5% level (designated RM20-0.5%), 1.0% level (RM20-1.0%), and 2.0% level (RM20-2.0%). The base commercial pellet was also tested unaltered and with 0.5% Kelco HV algin encapsulation. Recording of pellets presented and pellets apparently consumed by individual animals was maintained on a daily basis for each treatment.The RM20-2.0% bound pellet gave the best results in both physical stability and efficient biological utilization. The RM20-2.0% was followed in quality by the 0.5% encapsulated and 1.0% bound pellets. The unaltered M20 commercial pellet and 0.5% bound pellet were deemed unsatisfactory by the same criteria.     

Dissolved nutrient release from solid wastes of southern bluefin tuna (Thunnus maccoyii, Castelnau) aquaculture

Finfish pens are point sources of dissolved nutrients released from fish metabolism or degradation of solid wastes. Nutrients leaching from uneaten feed and faeces are not usually quantified in mass budgets for these systems, leading to an overestimation of fish retention or deposition to the seabed. In this study, we investigated nutrient leaching from pellets and baitfish feed as well as faeces of southern bluefin tuna (Thunnus maccoyii) into seawater. Faeces were nitrogen depleted (51–54 mg N g⁻¹ dw) and phosphorus enriched (62–72 mg P g⁻¹ dw) compared with feeds (83–111 mg N g⁻¹ dw and 17–21 mg P g⁻¹ dw). Less phosphorus was available for leaching from pellets and faeces of pellet‐fed tuna (5–6%) than from baitfish and faeces of baitfish‐fed tuna (17–21%). The proportion of soluble nitrogen in pellets (15%) was also lower than in baitfish and faeces (35–43%). Leaching loads for a feed conversion ratio of 5 were estimated as 22 and 26 kg N tonne⁻¹ growth when baitfish or pellets were used as feed respectively. Phosphorus loads were estimated as 15 and 4 kg P tonne⁻¹ growth respectively. More than 90% of nitrogen loads, and approximately 50% of phosphorus, are likely to be released into seawater before solid wastes reach the seafloor.     

Effect of organic fertilizer and formulated feed in pond culture of the freshwater prawn, Macrobrachium rosenbergii (de Man): pond productivity

Abstract. The application of different combinations and levels of pellet formulated feed and chicken manure to ponds stocked with Macrobrachium rosenbergii (de Man) did not result in any significant differences in water quality, sediment chemistry, or benthic macroinvertebrate populations. Water chemistry data indicated that all ponds were eutrophic. Chlorophyll was strongly correlated with total nitrogen, but not with total phosphorus, suggesting that nitrogen limited algal biomass. There was evidence that added organic matter was rapidly decomposed and mineralized. The sediments appeared to act alternately as sources and sinks of nutrients, although there was least variation in sediment nutrient levels in the treatment which received manure only. Applied pelleted feed was directly consumed by the prawns. In the absence of pelleted feeds, macrobenthos appeared to limit prawn growth after 1 month of culture. Simple nutrient mass-balance equations indicated that the losses of nitrogen, phosphorus and carbon from the treatments receiving feed were not dissimilar to previously reported values in finfish culture.     

Comparison of Ulva clathrata and the kelps Macrocystis pyrifera and Ascophyllum nodosum as ingredients in shrimp feeds

Three experimental diets were formulated to contain 33 g kg⁻¹ seaweed meals, made of wild brown algae (kelps) Macrocystis pyrifera (MAC) and Ascophyllum nodosum (ASC) or of a cultivated green alga Ulva clathrata (ULVA). The diets were fed to juvenile white shrimp Litopenaeus vannamei (1.6 g) for 28 days. Loss of dry matter (LDM) and loss of protein (LP) after 1 hour immersion in seawater, and distilled water absorption (WA) were analyzed in the pelleted diets, as well as shrimp weight gain, feed intake, feed conversion ratio (FCR), survival, protein efficiency ratio (PER) and body pigmentation. Feed intake, FCR and PER were corrected for nutrients preprandial losses in seawater. ULVA diet resulted in lower LDM, but a higher LP and also higher WA, indicating a modification of the pellet physical quality (better hydro stability). No significant differences in feed consumption and survival were found, but ULVA diet resulted in a slightly higher final weight (4.8 for ULVA versus 4.6 and 4.3 g for ASC and MAC), and better FCR (1.7 versus 1.9 and 2.1) and PER (2.0 versus 1.7 and 1.5), the differences with MAC diet being significant (Duncan, α = 0.05). Red color after cooking was markedly darker in the ULVA fed shrimp.     

Nutritional responses in rainbow trout (Oncorhynchus mykiss) fed diets with different physical qualities at stable or variable environmental conditions

Rainbow trout with initial body weight 1144 g were fed two diets with high (feed A) or low (feed B) water stability for 6 weeks. During the last 2 weeks either stable or fluctuating oxygen saturation, salinity and temperature was introduced. High water stability of the feed was associated with harder pellets, less dust formation and less broken pellets compared to feed with low water stability. During the first 4 weeks, feed intake was 23% higher in trout fed diet B than in those fed diet A. Fluctuating environment resulted in a severe drop in feed intake for both dietary groups. At termination of the trial, stomachs of trout fed feed B contained mashed pellets and free water and oil. Stomachs of trout fed feed A contained more intact pellets and little fluid. The apparent digestibility of protein, starch, dry matter and energy was highest in feed A. The apparent digestibility of P and Zn was highest at stable environment, and the absorption of P was highest from feed A. In conclusion, physical quality affected the nutritional value of the feeds, and differences in nutritional value at stable or fluctuating environment appeared to be related to feed intake.     

Comparative survival and growth performance of European lobster Homarus gammarus post‐larva reared on novel feeds

One approach to ongrow juvenile European lobster, Homarus gammarus, is to utilize land based rearing systems, incorporating automated feeding, individual culture and provision of stable pelleted feeds, preferably using sustainable ingredients. We initiated three feeding experiments to investigate the general suitability of ingredients produced from seafood by‐products as novel feeds for H. gammarus, in terms of promoting survival, development and growth of post‐larval lobsters from post‐larvae (PL) stage IV to the first juvenile stage (stage V). The first experiment was designed to screen an array of candidate, locally produced, novel protein sources on growth performance parameters. This initial experiment revealed that PL reared on a raw (i.e. wet, unprocessed shrimp) feed used as a reference showed superior performance to those reared on experimental feeds containing fishmeal, herring protein isolate or mussel meal; however, a novel type of shrimp meal, produced by flocculation from waste water, promoted the best PL performance of any experimental feed. A second experiment was designed to test the effect of drying method and to optimize the form of a wet shrimp reference feed used by lobster hatcheries. This showed that the performance of PL reared on experimental freeze‐dried shrimp feed was not significantly different to those reared on the wet, unprocessed shrimp used as a reference feed. However, lobsters offered experimental oven‐dried shrimp feed (with or without an immune supplement) resulted in significantly lower survival or growth performance. A third and final experiment was designed in an attempt to improve a candidate herring‐based protein source, by supplementing with nutrients found in shrimp. However, the results showed that PL reared on the wet reference shrimp feed still showed superior growth and survival than those reared on a herring feed alone, or supplemented with additives found in shrimp meal (either glucosamine, astaxanthin or both supplements combined). The high survival and growth, low incidence of moulting problems and high availability of waste shrimp material, suggest that non‐heat‐treated shrimp products are a promising feed ingredient for post‐larval European lobsters.     

Replacement of Soybean Meal by Lupin Meal in Practical Diets for Juvenile Penaeus monodon

The potential of lupin meal as an alternative protein source to soybean meal in isonitrogenous practical diets for the juvenile black tiger shrimp Penaeus monodon was evaluated through the studies of growth, digestibility and pellet water stability. Five isonitrogenous diets were formulated to contain 40% protein. Protein from dehulled Lupinus albus seed meal replaced 0, 25, 50, 75 and 100% of the protein from defatted soybean in the diets. Juvenile P. monodon (4.35 × 0.31 g) were assigned randomly and fed each test diet at a daily feeding rate of 5 % body weight for 42 d in triplicate tanks equipped with a flow-through sea water system. No statistically significant differences were observed in weight gain, feed intake, feed conversion ratio (FCR), protein conversion efficiency and apparent protein utilization of shrimp fed diets with 0, 25, and 50% replacement. Shrimp fed the diet with total replacement of soybean meal by lupin meal had the poorest performance (P < 0.05) with regard to the above parameters. Survival was similar (87%) for all dietary treatments. The apparent dry matter digestibility and apparent protein digestibility were similar for all diets ranging between 70.5 and 72.8% and 89.7 and 90.8%, respectively. There was no significant difference in whole body composition (dry matter, lipid, protein and ash) of shrimp on the various diets. The poorest pellet water stability was displayed by the diet with 100% replacement while the diet containing a combination of soybean meal and lupin meal (50% replacement) was the most stable. The results have demonstrated that dehulled lupin seed L. albus meal has good potential as a substitute protein source for up to 50% of the protein from defatted soybean meal and could be included up to 17% inclusion level in juvenile P. monodon practical diets with no adverse effects on growth, feed intake, FCR, survival, feed utilization, body composition, and digestibility coefficients of dry matter and protein.     

Effect of microencapsulated thyme essential oil on white spot virus-infected <Emphasis Type="Italic">Litopenaeus vannamei</Emphasis>

The present work was performed to investigate if feeding Litopenaeus vannamei with microencapsulated thyme essential oil (TEM, 1.05 g thyme essential oil per 100-g powder) adsorbed on commercial pellet feed was able to protect shrimps against white spot syndrome virus (WSSV) disease. Five treatments were tested: uninfected shrimp fed with commercial pelleted feed (T_C, negative control), WSSV-infected shrimp fed with commercial pelleted feed (T₁, positive control), WSSV-infected shrimp fed with commercial pelleted feed with 0.1% TEM (T₂), WSSV-infected shrimp fed with commercial pelleted feed with 0.5% TEM (T₃), and WSSV-infected shrimp fed with commercial pelleted feed with 1% TEM (T₄). At 72 h post infection, phenoloxidase activity of shrimps treated with 1% TEM did not show significant differences with T_C values but it was significantly higher than that of the other treatments (T₁, T₂, and T₃). Moreover, shrimps treated with T₄ presented absence of clinical signs of WSSV infection and their survival rate was significantly higher than that of T₁, T₂, and T₃ treatments. Therefore, 1% TEM seemed to protect shrimps against WSSV symptoms. Using microencapsulated thyme essential oil may help to fight against WSSV in shrimp farms.     

Efficacy of various coated materials to prevent nutrient leaching for Pacific white shrimp Litopenaeus vannamei commercial diets

The physical characteristics and leaching rates of water‐soluble compounds from shrimp feeds are major considerations in nutrient delivery. Yet, there is limited information on nutrient leaching from feeds or the mechanisms to minimize leaching. This study evaluated the efficacy of various coating agents on the physical characteristics and leaching of nutrients from commercial feeds for Litopenaeus vannamei. A series of diets were top coated with two lipid sources (fish or stearin oil) and two additives to the oil (5% wax or gelatin) at three levels (0, 1.5, and 3%). Physical characteristics and leaching of water‐soluble compounds were then characterized. The reduction of leaching was seen with the diets that were top coated with 1.5 or 3% oil, which significantly decreased the leaching of phenylalanine (Phe) after 30 min and 60 min of immersion. Adding 1.5 and 3% oil coating significantly decreased the pellet durability index. Adding gelatin as an additive to the oil significantly slowed sinking velocity and improved water stability and the pellet durability index of the diets. In all, results demonstrated that coating 1.5 or 3% fish or stearin oil decreases the leaching rate. Supplementing 5% gelatin in the coating material for diets can improve the performance of the diets.     

Digestibility of the defatted microalgae Nannochloropsis sp. and Desmodesmus sp. when fed to Atlantic salmon,Salmo salar

The aim of the study was to investigate the apparent digestibility coefficient (ADC) of defatted biomass derived from microalgae Nannochloropsis sp. and Desmodesmus sp. when fed to Atlantic salmon postsmolts in seawater. Two experiments, one employing cold‐pelleted and the other employing extruded pellets, were carried out to determine the ADC of dry matter (DM), protein, ash and energy. The test feeds consisted of a fishmeal‐based reference feed and the algal biomass, at a ratio of 70:30, and yttrium oxide as the inert marker. The ADC of DM and protein in fish fed microalgae‐incorporated cold‐pelleted feeds were significantly higher for Nannochloropsis sp. compared with Desmodesmus sp. The Nannochloropsis sp. inclusion in extruded feeds also led to higher ADCs of DM and energy compared with Desmodesmus sp. The extrusion processing significantly increased the ADC of ash in both defatted microalgae biomass, as well as ADCs of DM in Nannochloropsis and protein in Desmodesmus sp. In conclusion, the microalga Nannochloropsis sp. was more digestible than Desmodesmus sp., and extrusion processing can be used as a means to improve digestibility of certain nutrients.     

Effect of culture system on the nutrition and growth performance of Pacific white shrimp Litopenaeus vannamei (Boone) fed different diets

Two 8-week feeding trials were conducted with juvenile Pacific white shrimp, Litopenaeus vannamei (Boone) to compare the growth and performance of animals fed a series of experimental and commercial pelleted shrimp and fish feeds and dietary feeding regimes within an indoor running-water culture system and an outdoor zero-water-exchange culture system. The best overall shrimp growth performance was observed for animals fed the experimental shrimp diet and all-day feeding regime under outdoor zero-water-exchange culture conditions. Final body weight and average weekly growth rate under these conditions were 2.8 and 3.4 times greater, respectively, than animals of similar size fed with the same diet under indoor running-water culture conditions. Although direct comparison between indoor and outdoor culture systems is difficult because of the lower indoor water temperatures, and consequently lower mean daily feed intake of animals, it is believed that the higher growth and feed performance of animals reared under outdoor `green-water' culture conditions was primarily due to their ability to obtain additional nutrients from food organisms endogenously produced within the zero-water-exchange culture system. The most promising features of zero-water-exchange culture systems are that they offer increased biosecurity, reduced feed costs and water use for the farmer, and by doing so provide a potential avenue of moving the shrimp culture industry along a path of greater sustainability and environmental compatibility.     

Real‐time measurement of protein leaching from micro‐particulate larval fish feeds

The small size and high surface area to volume ratio of larval fish feed presents challenges for nutrient retention in micro‐particulate diets. A method for the accurate and rapid measurement of nutrient retention or loss from micro‐particulate feed in water is needed to help develop micro‐particulate feeds with good nutrient retention characteristics. The present study developed and validated an instrument method using fibre optic technology that measures protein leaching in real time. Larval fish feed particles of different sizes (100–500 μm) and formulations were measured. Under consistent experimental conditions, a feed could be assayed for the rate of mass loss and the half‐life or time of 50% total soluble mass loss. The results closely approximated natural decay models with coefficients of determination (r²) >0.95. The end result is a fast and accurate method to quantify and provide solid reference data for a feed formulation or particle size. Using this method allows different feeds to be compared and conclusions drawn for relative performance.