Effects of Rearing Conditions on Growth, Development and Moulting in European Lobster (Homarus Gammarus)
Middlemiss, Karen Lewanne
Date: 20 August 2014
University of Exeter
MbyRes in Biosciences
Chapter 2: Bacterial pathogens are a leading cause of disease in hatchery aquaculture systems and preventative methods such as probiotics as feed supplements and water additives is well documented. However, comparisons between the effectiveness of using probiotic water additives over traditional biocontrol methods are less understood. ...
Chapter 2: Bacterial pathogens are a leading cause of disease in hatchery aquaculture systems and preventative methods such as probiotics as feed supplements and water additives is well documented. However, comparisons between the effectiveness of using probiotic water additives over traditional biocontrol methods are less understood. This study assessed the effects of ultraviolet irradiation (UV), ozonation and Bacillus spp. as a water additive (probiotic), in the culture of European lobster in a semi-closed recirculation system. Stage I larvae were assigned to one of six treatment groups consisting of 1) ozone, 2) probiotic, 3) probiotic + ozone, 4) probiotic + ozone + UV, 5) ozone + UV, or 6) probiotic + UV, for 18 days. Growth and survival at stages I-V were measured on 1, 6, 11, 18, 24, 31 days post hatch and 1, 18, 24 and 31 days post hatch respectively. Bacterial counts of pathogenic Vibrio spp. in culture water were measured at 1, 4, 9, 14, 18 days post hatch. Lobsters were also exposed to a physiological fitness test (low salinity challenge) at megalopa stage IV, 7 days post treatment. Ozone was comparatively more beneficial than probiotic with increased live weight gain in the ozone treatment over probiotic between zoea stage IV-V (>5 mg). Survival rates were higher in the ozone treatment than probiotic on days 18, 24, and 31 (~66, ~117 and ~120%, respectively). There was a greater biomass in the ozone treatment than probiotic on days 18 and 31 respectively (~60 and ~116%, respectively). Total Vibrio spp. present in the ozone treatment was 99% less than in the probiotic treated culture water (day 18). Results between UV treatment groups showed significantly lower numbers of Vibrio spp. present in probiotic + ozone + UV culture water 4 days post hatch than ozone + UV (~10 fold higher) or UV + probiotic (~15 fold higher) and by day 18 probiotic + ozone + UV was significantly higher than ozone +UV (~8 fold higher). Osmoregulatory challenge test resulted in no significant differences in physiological fitness between any treatment groups. The present study clearly shows the effectiveness of O3 in aquaculture facilities for control of pathogens in the rearing of European lobster over either a probiotic water additive or UV irradiation. Chapter 3: The functional morphology of gill cleaning mechanisms is not well described in European lobster (Homarus gammarus). Brush like cleaning appendages called setae have evolved in many decapod crustacean species to control the accumulation of epibionts on gill structures that are vital for respiration, osmoregulation, acid-base balance and excretion of metabolic end products. Scanning electron microscopy was used to investigate structural development of the setae during larval and early juvenile stages of H. gammarus (larval stages I-III, megalopa stage IV and first juvenile stage V). Branchial cleaning mechanisms were further assessed by quantifying and classifying the progression of the microbial biofilm throughout a complete moult cycle from the megalopa (stage IV) to the first juvenile (stage V). Results showed denticulate (serrated) scales arranged along the distal end of a smooth setal shaft originating proximal to epipodite attachment. Setae occur only from larval stage III. Immediately after shedding (ecdysis) of the old exoskeleton, no epibionts were visible on the new cuticle. Microbial development was first evident on the gill filaments from day 10 postmoult, showing a significant 16-fold increase from day 10 to 15. This research provides new insights into the functional morphology of gill grooming in early developmental stages of H. gammarus and the role of moulting in microbial control. Chapter 4: Availability of calcium and carbonate ions from surrounding seawater influences the rapid calcification required by newly moulted marine crustaceans for survival postmoult. Calcium content of juvenile European lobster Homarus gammarus) was determined during intermoult, immediately postmoult and 24 hours postmoult. The fluxes (excretion or uptake) of NH4+ and HCO3- were measured at intermoult, 3, 6 and 24 hours immediately postmoult in high and low alkalinity seawater (2000 and 1000 µeq/l). Of the combined total of calcium in the newly moulted animal and shed exoskeleton (exuvia), ~80 % of the calcium was found in the exuvia. The total calcium content of animal and exuvia combined was 44 % less than the intermoult total body calcium. At 24 h postmoult total body calcium was 50 % of the intermoult stage. Net flux of NH4+ was the same in both alkalinity treatments groups. Postmoult uptake of HCO3- was substantially reduced in the low alkalinity seawater treatment at all three time points (32, 29 and 42 % at 3, 6 and 24 h postmoult, respectively). HCO3- uptake in high and low alkalinity seawater peaked at 6 hours with a decrease between 6-24 h postmoult (~20 and 16 % respectively). Exoskeleton calcification was still taking place 24 h postmoult. Net acid excretion (equivalent to net base uptake) was significantly lower in low alkalinity seawater treatments at 3, 6 and 24 h postmoult (~26, 23 and 26 %, respectively). High and low alkalinity seawater treatment net acid fluxes increased over the first 6 h postmoult with a decrease between 6 and 24 h postmoult (~23 and 26 % respectively). Within intensive aquaculture systems, reduced alkalinity is a common occurrence and results showed that low alkalinity substantially slows the calcification rates in juvenile H. gammarus after a moult.
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