Danielle Johnston

Dietary carbohydrate/lipid ratios and nutritional condition in juvenile southern rock lobster, Jasus edwardsii

Abstract The availability of formulated diets is considered economically imperative if rock lobster aquaculture, based on the collection and ongrowing of puerulus, is to progress. Central to the development of diets is an understanding of the nutritional requirements of the species. This study determined the effect of different dietary carbohydrate/lipid ratios (17:1, 5:1, 2:1, 0.8:1) on the growth and nutritional condition of juvenile southern rock lobsters, Jasus edwardsii, by measuring standard growth parameters, proximate composition of the whole body and digestive gland, and from a histological investigation of the digestive gland. Four replicate groups of eight lobsters (initial weight 5.08±0.98 g (mean±S.D.)) per diet treatment were held in 50 l tanks, in a recirculating system at 18 °C for 84 days. Maximum growth and the highest levels of lipid and dry matter in digestive glands and whole bodies was found in lobsters fed a diet containing 27% carbohydrate and 13.5% lipid (2:1 ratio) suggesting that of the four experimental diets, this diet provided the best balance of lipid and carbohydrate. Digestive gland histology supported this conclusion and lobsters fed low carbohydrate, high lipid diets were in the best nutritional condition, with high lipid accumulation, and structurally sound epithelial cells. Digestive gland epithelial cells of lobsters fed the high carbohydrate, low lipid diets were compressed, of inconsistent shape and size, with low lipid accumulation. Histology is therefore seen as a feasible method, in addition to growth and proximate composition data, to further examine the effect of diets in nutritional studies of crustaceans.

Feeding Biology of Spiny Lobster Larvae and Implications for Culture

Concern for the sustainability of spiny lobster (Decapoda: Palinuridae) fisheries has created significant interest in their aquaculture. However, attempts to culture spiny lobsters from eggs to puerulus have been largely unsuccessful, hampered by provision of unsuitable diets during the long phyllosoma larval phase. This review summarizes the current understanding of phyllosoma feeding and digestive biology, and collates the findings of previous culture trials. It draws attention to gaps in our knowledge and suggests avenues for future research aimed at bridging these gaps. Finally, it makes recommendations for culture diets based on our current understanding. Problems associated with the provision of live feeds such as Artemia salina (e.g., bacterial contamination) suggest that formulated diets may be most appropriate. An improved understanding of the feeding behavior, natural dietary preferences, nutritional profiles, and digestive capabilities of phyllosoma will identify the size, texture, and nutritional characteristics of a suitable formulated diet. Based on recent morphological and behavioral evidence presented in this review, soft, possibly microencapsulated diets (gelatin/alginate coated) appear to be the most promising formulated diet for early stage larvae, followed by fleshier prey (such as fish larvae) in later stages.

Mouthpart and foregut ontogeny in phyllosoma larvae of the spiny lobster Jasus edwardsii (Decapoda; Palinuridae)

Mouthpart and foregut structure indicates that Jasus edwardsii phyllosomas ingest soft fleshy foods such as gelatinous zooplankton. Mouthpart morphology changes little during larval development, indicating that ingestive capabilities and external mastication are well developed from an early age. However, the density and complexity of setation and robustness of individual mouthparts increases with age, suggesting a greater capacity to ingest larger prey during development. The foregut consists of a single chamber with a number of well-developed grooves, ridges, and setae but lacking a gastric mill. The primary role of the foregut is mixing, sorting, and filtering particles, preground by the mouthparts. Phyllosomas have been divided into early (stage I-III), mid (IV-V), and late (VI-X) stages based on the development of the filter press and main brushes. Increasing robustness of setation and complexity of the foregut suggest that the texture of prey becomes more muscular (fibrous) with larval development. The results presented here suggest that early-stage phyllosoma would benefit from a diet comprising soft gelatinous items, whereas late-stage phyllosomas are better prepared to deal with larger, fleshy prey. The changes in structural characteristics with age should also serve as a guide in the development of formulated diets.

Shrimp yields and harvest characteristics of mixed shrimp-mangrove forestry farms in southern Vietnam: factors affecting production

Shrimp yields and harvest characteristics were monitored at mixed shrimp–mangrove forestry farms in two state forestry–fisheries enterprises, Tam Giang 3 and 184, in Ca Mau province, southern Vietnam. The aim was to identify key factors contributing to poor and declining shrimp production in the region over recent years. Shrimp yields were highly variable between farms but were generally low with mean annual yields of 286±106 kg ha−1 yr−1 and income of 388±146 USD ha−1 yr−1. Secondary fisheries products, such as fish and mud crabs, increased total farm production by 24% (54 kg ha−1 yr−1) and income by 14% (71 USD ha−1 yr−1). Shrimp yields peaked between July–October and March–May, which is consistent with the traditional “Mua” and “Tong” harvest seasons, respectively. Yields were significantly higher at enterprise Tam Giang 3 and were generally higher at extensive farms than traditional farms. A correlation analysis of water quality and technical parameters revealed that pond depth (r=0.62), maximum fluctuation in pond depth (r=−0.55) and ammonia concentration (r=−0.63) were significantly correlated with shrimp yields (P<0.05). Stepwise multiple regression revealed the model: Yield=1.73–7.8*NH3–N+0.03*Pond Depth (r2=0.63). Metapenaeus ensis and M. lysianassa are the dominant shrimp species cultured, representing 48–50% and 31–32% of harvests, respectively. Penaeus indicus is the third most important species, although it represents a much smaller proportion (6.7–9.7%) of total harvest. All three species vary in abundance with season, with M. ensis being dominant in the wet and M. lysianassa dominant in the dry. The size of shrimp harvested is small, with a mean total length of 49.7±0.18 mm and 50.6±0.2 mm for M. ensis and M. lysianassa, respectively. Key factors contributing to poor and declining shrimp yields in Ca Mau province include inappropriate management techniques and pond design, poor wild seed recruitment, and reliance on small, low-value Metapenaeids as culture species. Recommendations to improve current farm production are presented.

Diet immersion time: effects on growth, survival and feeding behaviour of juvenile southern rock lobster, Jasus edwardsii

Abstract The effect of water immersion time of a formulated shrimp diet on growth, survival, food conversion and carapace colour of juvenile southern rock lobster, Jasus edwardsii , was determined during a 16 week growth trial. Lobsters were fed one of five diets: pre-soaked shrimp diet (0.5, 2, 4 and 8 h) or non-soaked shrimp diet (0 h). Despite a significant loss in dry matter, protein, ash and astaxanthin from the diet as a result of pre-soaking, there was no effect on the growth, survival, food conversion or carapace colour of lobsters. Feeding behaviour of juvenile J. edwardsii was assessed using glycine, taurine and betaine, previously identified as strong chemoattractants to other crustaceans. Quantification of the antennular grooming frequency (AGF) was identified as the best method of assessing chemoattractant detection in J. edwardsii . The highest rate of AGF was observed in response to glycine at concentrations of 10 −4 to 10 −6 mol l −1 . AGF was subsequently used to assess the excitatory capacity of shrimp diet extract and fresh mussel ( Mytilus edulis ) extract. Two separate experiments were performed to determine the influence of water immersion on the excitatory capacity (ability to detect the source-(AGF)) and the attractability (capacity to attract to the source-(foraging preference)) of the shrimp diet in comparison to that of fresh mussel flesh. The excitatory capacity of the non-soaked shrimp diet, soaked shrimp diet and fresh mussel extracts were similar. However, the attractability of the non-soaked shrimp diet was greater than soaked shrimp diet and mussel flesh. Lobsters are capable of detecting the shrimp diet regardless of prolonged exposure to water; however, they will selectively move towards a “fresh” rather than a “stale” diet. The results of this study show that the loss of chemoattractants and nutrients from a shrimp diet, caused by leaching, had little impact on the culture performance of J. edwardsii . Thus, even though some lobsters have a slow feeding response and may not feed for several hours after being fed, the dispensation of feed only once per day will not impact on culture performance. However, the influence of leaching on the performance of diets specifically developed for J. edwardsii will need to be re-assessed.

Pelagic processes in extensive shrimp ponds of the Mekong delta, Vietnam

Rates of pelagic primary production, respiration, and bacterioplankton dynamics were measured in relation to water quality parameters in three extensive shrimp ponds in the Mekong delta, Vietnam. There were few consistent differences in pelagic characteristics among different locations within these ponds, among the three ponds, or between the ponds and adjacent river water. Rates of primary production ( uptake) ranged from <1 to 94 mg C m−3 d−1. Rates of gross primary production (light–dark bottle technique) ranged from −184 to 2697 mg C m−3 d−1. Rates of pelagic respiration ranged from 60 to 3783 mg C m−3 d−1. Primary production rates measured by oxygen flux were greater than those measured via uptake, with P/R ratios varying widely (−0.45 to 3.4), but the mean P/R at each site was <1 with a grand mean among ponds of 0.7. Bacterioplankton numbers (mean range: 0.2 to 27.2×108 cells ml−1) and productivity (range: 2.5 to 297.3 mg C m−3 d−1) did not vary consistently among ponds with season. Mean bacterioplankton growth rates were fastest (μ=0.29 d−1) in the pond with highest shrimp production and slowest in the poorest yielding pond (μ=0.08 d−1). The primary production and respiration rates, and bacterioplankton dynamics, indicate that these pond waters are net heterotrophic. Plankton measurements rarely correlated with changes in physicochemistry (pH, dissolved O2, salinity, temperature) or nutrient concentrations as within-site and temporal variability were large for most parameters. The diurnal cycles of physicochemical characteristics were similar to those measured in other unfertilized, low-alkalinity ponds, but these cycles were dampened by intense rainfall. Our data indicate that low net primary production, high rates of respiration, moderate rates of bacterioplankton production, high suspended solid and nutrient concentrations, low and very variable pH and dissolved O2 concentrations, and variations in salinity due to intense rainfall episodes limit shrimp production in these extensive ponds.

Developmental changes in the structure and function of mouthparts of phyllosoma larvae of the packhorse lobster, Jasus verreauxi (Decapoda: Palinuridae)

Abstract Mouthpart morphology and feeding behaviour of Jasus verreauxi phyllosomas (instars 1–13) were examined using scanning electron microscopy and video analysis, respectively, to better understand ingestion and processing mechanisms and to identify developmental changes in feeding biology. The density, robustness and complexity of mouthpart setation increased with development, oral field increased and there were a greater number of spinose projections on maxillae 1 in mid and late instar phyllosomas. The second and third maxillipeds were able to sweep a larger area due to their increased length, which effectively increased the size of the oral field. Changes in feeding behaviour were consistent with these morphological differences between instars. In late instars, the shredding and tearing efficiency of maxillae 1 increased, larger pieces of prey were pushed between the mandibles, and the mandibles were able to effectively grind food due to a slight rotation away from the transverse plane. Both morphological and behavioural observations suggests that the absolute size range of prey increases with phyllosoma body size and the prey processing (i.e. ability to capture, manipulate and grind prey) becomes more efficient with development. We suggest early instar phyllosoma are most suited to a diet comprising softer prey items, whereas later-instar phyllosoma are better equipped to deal with larger, fleshier prey.

Shrimp seed recruitment in mixed shrimp and mangrove forestry farms in Ca Mau Province, Southern Vietnam

Abstract The densities of shrimp seed recruited into ponds at mixed shrimp and mangrove forestry farms in Ca Mau province, southern Vietnam, were monitored semi-continuously from 1996 to 1998 to determine whether shrimp culture in the region is recruitment-limited. The numbers of shrimp seed lost during harvests were also monitored to assess whether current management strategies contribute to low stocking densities and pond production. Shrimp seed recruitment densities were low and highly variable with farms recruiting less than 1 postlarva m−3 between August 1996 and May 1997. Recruitment varied significantly with season (P=0.0014), with peaks in October to November and April to May, the former having the highest recruitment densities. This trend is consistent with seasonal offshore spawning events in southern Vietnam. Recruitment did not vary significantly between day and night (P=0.8), although data suggest that recruitment may be higher at night during peak recruitment months (November, February). Postlarval densities were significantly higher on the first day (24 h) of each spring tide period (P=0.0046). Mean total length of shrimp seed was 13.72±0.35 mm, which indicates that farms are recruiting postlarvae approximately 15–20 days post-metamorphosis (PL15–20), or 35 days post-hatch, into ponds. Recruitment densities were higher at farms on rivers than at farms on small canals during March/April 1998, which corresponded with peaks in immigration of postlarvae into estuaries on tidal currents at this time. The numbers of shrimp seed lost during harvests were high, reducing net recruitment and net stocking densities to 0.15 postlarvae m−2 from a potential gross stocking density of 0.35 postlarvae m−2. Shrimp culture in Ca Mau province is recruitment-limited. This is a major factor contributing to low shrimp yields in the region. Current harvesting techniques need to be modified to reduce postlarval losses and improve overall stocking densities and pond production.

Developmental changes in foregut functioning of packhorse lobster, Jasus (Sagmariasus) verreauxi (Decapoda : Palinuridae), phyllosoma larvae

The development of foregut structure and digestive function was examined in Jasus (Sagmariasus) verreauxi phyllosomas (instars 1-13) using resin histology and video analysis. Early instar (1-3) phyllosoma had very simple anterior foreguts with little differentiation into ventral and dorsal chambers, no filter press and small lateral comb-row setae. By mid instars (4-7), the filter press had developed and ventral and dorsal chambers of the foregut were distinct. The number and robustness of lateral setae had increased and a dense mat of anterior floor setae had formed. The filter press became increasingly complex in later-instar (8-13) larvae and dense robust lateral comb-row setae, main brushes and a thick mat of anterior floor setae forming longitudinal channels had developed by this stage. The mechanism of food digestion remained similar between instars but changes in foregut structures suggest that the degree of internal mastication, filtration and capacity to sort and mix particles improved with age. This research has implications for artificial diet development in crustacean culture and understanding dietary shifts during larval development.

ONTOGENETIC CHANGES IN THE STRUCTURE AND FUNCTION OF THE MOUTHPARTS AND FOREGUT OF EARLY AND LATE STAGE PANULIRUS ORNATUS (FABRICIUS, 1798) PHYLLOSOMATA (DECAPODA: PALINURIDAE)

Abstract Structure of the mouthparts and foregut of Panulirus ornatus phyllosomata (stages I-VI hatchery reared, IX-X wild caught) were examined using scanning electron microscopy and histology to gain an understanding of ingestive and digestive processing mechanisms, to identify potential shifts in diet during development, and to suggest appropriate physical characteristics for the development of a suitable formulated diet for commercial aquaculture of this species such as size, texture, and buoyancy. Mouthpart and foregut structure indicates that P. ornatus phyllosomata are capable of ingesting zooplankton of any hardness during this life history stage and are only limited by their ability to capture and manipulate prey as the mandibular molars are well developed to masticate prey further. Mouthpart morphology changes little during development, however, the disposition of the mouthparts and size of the mouth aperture increases with each successive stage of development, suggesting a greater capacity to manipulate and ingest larger prey. The foregut of all developmental stages consists of a single chamber, with well-developed grooves, channels and setae, but lacks a gastric mill. Presence of well-developed main brushes, lateral setae, and development of a functional filter press at stage IV suggests an increased ability to triturate and filter prey internally, reducing both the time spent externally manipulating prey with the mouthparts and the vulnerability to predation in the open ocean. The results presented here suggest that formulated diets larger than > 428 μm, with a firm/hard consistency that allow the dactyli of the second and third maxillipeds to penetrate the diet without causing fouling of the setae would be suitable.