Feed intake rate and extent relationship to foregut capacity

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Feed intake rate and extent: relationship to foregut capacity

Introduction

Poor food consumption has been identified as a possible reason for the slow growth in spiny lobsters raised on dry formulated diets (Glencross et al., 2001; Johnston et al., 2007; Williams, 2007). For example, no difference in food consumption was found among a range of formulated diets fed to juvenile spiny lobsters Panulirus cygnus (Glencross et al., 2001) and Jasus edwardsii (Ward et al., 2003). It was also observed that P. ornatus juveniles were less inclined to eat after dry formulated feed pellets had been immersed in water for 1-2 h, whereas shucked mussel remained attractive to the lobsters for 10 h or more after immersion (Williams et al., 2005). Poor chemoattraction and palatability of formulated diets compared to fresh mussel have been suggested as being the major causes for the low food consumption and consequently growth of P. ornatus (Williams et al., 2005). However, for the spiny lobster, J. edwardsii, from temperate waters, previous studies have reported very similar dry matter intake for a wide range of formulated diets and fresh mussel, varying from 2% BW day^-1 in small juveniles (2-7 g wet weight) to 1% BW day^-1 in larger juveniles (13-20 g wet weigth) (Crear et al., 2000, 2002; Thomas et al., 2003; Tolomei et al., 2003; Ward et al., 2003). Tolomei et al. (2003) showed that the excitatory capacity of the extracts of a commercial shrimp diet and fresh mussel were similar, and the attractability of a formulated diet was greater than for mussel in J. edwardsii left unfed for 48 h. In addition, other studies have shown that feeding lobsters several meals a day does not improve feed intake or growth (Bordner & Conklin, 1981; Thomas et al., 2003; Cox & Davis, 2006; Jones, 2007; Johnston et al. 2008). This is unusual as theoretically more frequent delivery of feed should increase attraction, palatability and reduce leaching from diets, thereby resulting in higher utilisation, feed intake and growth (Sedwick, 1979).
Nutritional studies have often relied on growth, food consumption, food conversion ratio and behavioural observations to determine the attractiveness and palatability of formulated diets for spiny lobsters (Tolomei et al., 2003; Williams et al., 2005). At present, data relating to food intake rate and maximum consumption in a single feeding event are lacking for spiny lobsters, despite their relevance to optimise formulated diet palatability and to develop effective strategies for delivering feed. Spiny lobsters are intermittent nocturnal feeders and differ fundamentally from penaeid shrimps which display virtually continuous ingestion throughout the day (Nunes & Parsons, 2000; Geddes et al., 2001). Shrimps achieve high levels of food consumption, despite the relatively small capacity of their foregut (2-3% BW), because of high rates of foregut filling (10 min) and emptying (2-4 h) (Nunes & Parsons, 2000). The contrary can be expected for lobsters which display much slower rates of gut clearance (Barker & Gibson, 1977; Kurmaly et al., 1990; Sarda & Valladares 1990). Despite substantial research in diet development for spiny lobsters (Williams, 2007), relatively little is known about the digestive processes occurring after the ingestion of formulated diets and the potential for a negative effect on food consumption. There is a need to determine the relationship between body size and foregut capacity and its potential to limit food intake. It is generally assumed that the higher weight to volume ratio of dry formulated diets compared with fresh food will result in higher dry matter feed intake for a single feeding event (Ruohonen et al., 1997). Yet, cultured fish are known to be able to compensate for large differences in dietary water content so they can achieve similar dry matter intake (Ruohonen et al., 1997). Dry diets generally tend also to require moisturising before digestion can begin, with the moisture coming from internal secretion and ingestion, resulting in higher food volume in the fish stomach (Ruohonen et al., 1997).
This study measures feed intake on three size-classes of juvenile J. edwardsii, fed the flesh from freshly opened mussel (Perna canaliculus) and the dry formulated diet. The aims of the study are to determine; 1) the effect of body size and diet type on the rate of feed intake, and, 2) to establish if the maximum feed intake is limited by the volume of the foregut (i.e., foregut capacity).

Materials and methods

Experimental diets and design

The study used two diets, the dry formulated diet (see Table 3.1. for ingredient composition) and fresh mussel, P. canaliculus, which was held live in tanks of flowing seawater until required for the experiments. The proximate composition of the two diets was broadly similar when expressed on a dry weight basis (Table 2.1.) and previous research has demonstrated that both diets are nutritionally adequate (Simon & James, 2007). However, the formulated diet was more nutrient dense owing to a smaller moisture component compared with wet mussel flesh (Table 2.1.). For the feeding experiments, only the mussel mantle and gonad were used and hereafter referred to as mussel flesh (the same definition is used in the two following chapters as well). These mussel parts were removed from the valves of freshly opened mussels as a single piece of flesh and drained for five min on 250 µm sieves. This allowed minimising fluctuations in moisture level between meals. As a result, the moisture content of the mussel flesh used for experiments (77.0%) was slightly lower than that of the whole mussel (79.8%).
edwardsii juveniles caught yearly between 2004 and 2006 in crevice collectors deployed in Gisborne were grown communally on opened fresh mussel P. canaliculus at ambient seawater temperature (i.e., 9-18 °C). The spiny lobsters were fed a mixed diet of dry formulated diet and fresh mussel three times weekly to satiation for one month before the experiment. Three size-classes of juveniles were established arbitrarily according to their wet body weight: Size one, S1 (initial mean BW ± S.D. 18.8 ± 1.2 g); S2 (42.0 ± 2.6 g); and S3 (82.9 ± 4.9 g). Healthy intermoult lobsters with a complete set of functional feeding appendages were selected and stocked individually in tanks to avoid conspecific interactions. Lobsters were acclimated for 10 days to their respective experimental tank and diet (i.e., mussel flesh or formulated diet) before the start of the experiment. Feeding experiments were performed over three weeks for each size-class consecutively (i.e., a total of nine weeks) in transparent-plastic aquaria: 0.26 m × 0.15 m × 0.18 m (depth), 6 l. Aquaria received flow-through sea-water that had been cartridge-filtered (1 µm) at a constant flow rate of 0.6 l min^-1 and at a temperature of 18 ± 1 ºC. The experimental tanks were illuminated with one 50 W incandescent light bulb (low light levels <0.5 µmol m^-2 s^-1) at a photoperiod of L12:D12 to ensure the feed intake of lobsters would not be negatively affected by bright light levels (Bordner & Conklin 1981). Water quality was similar to previous J. edwardsii growth studies (Crear et al., 2000, 2003; Simon & James, 2007).

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Feed intake

Feed intake was determined as the amount of dry matter ingested per lobster during a feeding event (i.e., meal). To calculate the rate and extent of feed intake, a total of 30 lobsters per size-class were allowed to feed on their respective diet for different randomly assigned meal durations (i.e., 0.5, 1, 2, 4, and 5 h). A non-feeding period of 48 h between meals was established to stabilise feed intake at each meal and to ensure lobsters returned to a pre-feeding basal metabolic state before the next meal (Crear & Forteath, 2000; Radford et al., 2004). Individual lobsters were re-used several times in the experiment after a four day recovery period during which they were fed twice every 48 h on their respective diet for 5 h. Re-used lobsters were randomly assigned a new experimental meal duration. As feeding declined or completely ceased around ecdysis, data obtained 96 h before and after ecdysis events were not used (14.5% of instances). A total of 366 feed intake measurements were analysed (Table 3.2.).
Weight measurements were determined to the nearest milligram using a precision AG204 Mettler Toledo balance. To calculate feed intake, a known quantity of food was offered above satiety levels (3% BW). Uneaten formulated diet was recovered by micro-filtering the water using 1.2 µm pre-weighed glass microfibre filter papers (GM/C, 47 mm circles). Micro-filtration allowed complete collection of the finest fragments of uneaten food arising from manipulative losses while lobsters were feeding on the dry formulated diet. Filter papers were gently rinsed with distilled water to remove salts (Ward et al. 2003). Uneaten fresh mussel flesh was siphoned directly on allocated 250 µm sieves as no manipulative losses were apparent for this diet. Uneaten feed samples were individually dried in small plastic trays at 75 ºC in a forced-fan oven for at least 20 h to achieve constant weight (Crear et al., 2002; Sheppard et al., 2002). The dry weight of the food provided at the start of a feeding event was back-calculated by accounting for the diet dry matter content and losses during immersion and the recovery procedure (i.e., water stability). Water stability was calculated by introducing a known amount of food in tanks (formulated diet, n=58; mussel flesh, n=45) without lobsters and measuring recovered food after different immersion periods (i.e., 1-5 h) in a similar manner, and with similar water condition, as for feed intake calculation.

1. CHAPTER ONE – GENERAL INTRODUCTION
1.1. Introduction
1.2. Objectives of the present thesis
1.3. Notes on the thesis structure .
2. CHAPTER TWO – PERFORMANCE ASSESSMENT OF FORMULATED DIETS IN A NOVEL SEA-CAGE DESIGN
2.1. Introduction
2.2. Materials and methods
2.3. Results
2.4. Discussion
3. CHAPTER THREE – FEED INTAKE RATE AND EXTENT: RELATIONSHIP TO FOREGUT CAPACITY
3.1. Introduction
3.2. Materials and methods
3.3. Results
3.4. Discussion
4. CHAPTER FOUR – APPETITE REVIVAL AND FOOD CONSUMPTION UNDER DIFFERENT FEEDING FREQUENCIES: RELATIONSHIP TO GUT EVACUATION
4.1. Introduction
4.2. Material and methods
4.3. Results
4.4. Discussion
5. CHAPTER FIVE – POST-PRANDIAL CHANGES IN DIGESTIVE ENZYME ACTIVITIES AND DIGESTIVE GLAND STRUCTURE IN RESPONSE TO FEEDING ON NATURAL AND FORMULATED DIETS
5.1. Introduction
5.2. Materials and methods
5.3. Results
5.4. Discussion
6. CHAPTER SIX – IDENTIFICATION OF DIGESTIBLE CARBOHYDRATE SOURCES: IN VITRO DIGESTIBILITY AND POSTPRANDIAL HAEMOLYMPH GLUCOSE CONCENTRATIONS
6.1. Introduction
6.2. Materials and methods
6.3. Results
6.4. Discussion
7. CHAPTER SEVEN – APPARENT DIGESTIBILITY OF DIFFERENT CARBOHYDRATES, BINDERS AND FISHMEAL PARTICLE SIZES IN FORMULATED DIETS
7.1. Introduction
7.2. Materials and methods
7.3. Results
7.4. Discussion
8. CHAPTER EIGHT – GENERAL DISCUSSION
8.1. The nutritional benefits of biofouling
8.2. Towards the commercialisation of sea-cage technology for spiny lobster ongrowing
8.3. Feeding and its relation to digestive physiology in cultured Jasus edwardsii juveniles
8.4. Carbohydrate digestion in Jasus edwardsii juveniles
8.5. Towards the successful development of formulated diets for spiny lobsters
8.6. Conclusion
LIST OF REFERENCES