The effect of photoperiod on growth, survival, colour and activity of juvenile southern rock lobster, Jasus edwardsii

Juvenile (1–10 g) southern rock lobsters, Jasus edwardsii, were subjected to five photoperiods [0L(light):24D(dark); 6L:18D; 12L:12D; 18L:6D; 24L:0D] during a 112‐day trial, and growth, survival, colour, food consumption and activity were examined. Lobsters grown under the 6L:18D and 24L:0D photoperiods had significantly lower (P < 0.05) final mean weight and specific growth rate than any other treatments. Photoperiod had no effect on survival or colour of lobsters. Food consumption differed significantly during the first week of the trial; after 5 weeks, food consumption was similar in all treatments. Major peaks in activity occurred during dark periods for lobsters exposed to photoperiods that had a light:dark regime. Activity of lobsters exposed to continuous light or dark regimes remained constant and at low levels during the 24‐h period. Food consumption or activity does not appear to determine the rate of growth of lobsters in the different photoregimes. One over‐riding outcome of this and other studies on photoperiod is that the growth and survival response of juvenile J. edwardsii was not significantly better than those of the standard 12L:12D cycle.     

The effect of PUFA enriched Artemia on growth, survival and lipid composition of western rock lobster, Panulirus cygnus, phyllosoma

Western rock lobster, Panulirus cygnus, phyllosoma were grown from hatching to stage IV. Larvae were fed with Artemia enriched with a (i) base enrichment (Base) containing 520 g kg^?1 squid oil or tailor made enrichments in which oils high in polyunsaturated fatty acid (PUFA) have been added at the expense of squid oil. These treatments were (ii) base enrichment supplemented with docosahexaenoic acid (DHA) rich oil, (iii) base enrichment supplemented with arachidonic acid (AA) rich oil, or (iv) base enrichment supplemented with DHA and AA (D + A) rich oils. Total survival of phyllosoma to stage IV was high, with no significant difference between treatments (range 12.3–17.5%). By stage IV, the larvae fed the DHA or AA enriched Artemia were significantly larger (3.33 mm length) than larvae fed the Base or D + A enriched Artemia (3.18–3.24 mm length). Phyllosoma were sampled at stages II and III for biochemical analysis. The major lipid class (LC) in all phyllosoma was polar lipid (PL) (88.9–92.4%), followed by sterol (ST) (6.2–9.7%). Triacylglycerol (TAG), free fatty acid (FFA) and hydrocarbon/wax ester were minor components (≤1%) in all phyllosoma samples. In contrast, the major LC in all enrichments and enriched Artemia was TAG (76.3–85.1% and 53.4–60.2%, respectively), followed by PL (11.4–14.8% and 30.6–38.1% respectively). The main fatty acids (FA) in phyllosoma were 16:0, 18:1n‐9, 18:1n‐7, 18:0, AA, eicosapentaenoic acid (EPA) and DHA. Addition of AA, and to a lesser extent DHA, to enrichments resulted in increased levels of those FA in Artemia and phyllosoma compared with the Base enrichment. This was particularly evident for stage III larvae. Comparatively, elevated growth for phyllosoma to stage IV was achieved with DHA and AA enriched diets. Our findings highlight the importance of lipids and in particular essential long‐chain PUFA, as nutritional components for phyllosoma diets.     

Morphological and biochemical characteristics of phyllosoma after photothermal manipulation of reproduction in broodstock of the spiny lobster, Jasus edwardsii

The consequences of photothermal manipulation of reproduction in Jasus edwardsii broodstock on the morphology of newly hatched larvae and their biochemical characteristics were examined. The treatment of compressed temperature and photoperiod delayed the time of moult, mating and egg extrusion, but reduced the period until larval hatch, and reduced the hatching duration in individual females compared to the ambient treatment of simulated natural photoperiod and water temperature. Thus, the availability of phyllosoma for hatchery rearing was extended. However, the broodstock in the compressed treatment produced smaller phyllosoma and more larvae failed to develop beyond the naupliosoma stage than animals from the ambient cycle. Phyllosoma from the compressed treatment contained a higher proportion of polar and triacylglycerol lipid classes, lower wax esters, elevated levels of the essential fatty acid docosahexaenoic acid, a higher ratio of n-3/n-6 fatty acids, and lower levels of ascorbic acid. The changes in larvae from the compressed treatment may adversely affect their viability, and are probably due to the higher water temperatures experienced during late embryonic development.     

The effect of temperature on the growth, survival and food consumption of the east coast rock lobster Panulirus homarus rubellus

The successful culture of the east coast rock lobster Panulirus homarus rubellus is reliant, among other factors, on the provision of optimal water quality for growth and survival. This study investigated the effect of temperature over a range of 9.7 °C (18.9 ± 0.7 °C to 28.6 ± 1.5 °C) on the growth and survival of juvenile (40.4 ± 9 mm CL; 63.64 ± 12.05 g) P. h. rubellus fed a diet of fresh mussel flesh. Specific growth rate (SGR) was significantly different between temperatures (p = 0.01), with the highest values recorded for the 24 and 28 °C treatments. There was no significant difference in moult increment (MI) between temperatures in terms of both an increase in weight (p = 0.83) and carapace length (p = 0.54). Intermoult period (IMP) differed significantly between temperatures (p = 0.0015) with mean IMP lowest at 24 °C, although not significantly different from the means of the 26 and 28 °C treatments. IMP was highest at 19 and 21 °C. Apparent feed intake was significantly different between treatments (p < 0.0001) and exhibited a strong positive correlation with increasing temperature (y = − 1.67 + 0.16x ; r² = 0.81). Food conversion ratio (FCR) differed significantly between temperatures (p = 0.02) with 24 °C exhibiting the most efficient FCR. Results indicate that efficient growout of juvenile P. h. rubellus, in terms of both growth and food conversion efficiency, is obtainable at 24 °C.     

The effects of temperature and diet on the survival, growth and food uptake of aquarium-held postpueruli of the rock lobster Jasus lalandii

Aquaculture of the rock lobster Jasus lalandii has been considered, but is hindered by a paucity of knowledge about conditions that promote yields. This study investigated the influences of temperature and diet on the growth of aquarium-held postpueruli of J. lalandii. First, postpueruli (11.5±0.2 mm CL) were exposed to temperatures spanning 12–24 °C for a total time period of 77 days, while being given a constant diet of mussel flesh. Under these conditions, intermoult period (IMP) was longest at 12 °C (50.6±1.2 days) and at 24 °C (>57 days), and shortest at 18 °C (35.5±1.1 days). Growth increments (GI) were large at 12–18 °C, smaller at 21 °C and negative at 24 °C. Survival was 100% at 12–16 °C, above which mortalities rose to 70% at 24 °C. Food consumption, body mass and condition all peaked at 18 °C. Thus, growth was optimal at 18 °C, but survival greatest at 12–16 °C.

Second, diet-controlled experiments examined the effects of three different diets (blue mussel, commercial shrimpfeed or an alternation of the two) on survival, growth (IMP and GI) and food uptake of postpueruli (11.0±0.3 mm CL) held at 18 °C for a total time period of 77 days. Feeding rate, average growth, body mass and condition were all highest on the mussel diet, and lowest on the shrimpfeed, and the postpueruli consumed more mussel flesh than shrimpfeed. There was little difference in survival of postpueruli subjected to the three diet treatments.

A diet of exclusively blue mussel yielded higher growth, body mass, condition and food uptake than a diet of either shrimpfeed alone or an alternation of mussel and shrimpfeed. The postpueruli acclimated well to culture conditions and survived on a diet of artificial pellets, thus showing good potential for mariculture. On the present evidence, greatest returns are likely at 16–18 °C and with a diet of mussel flesh.     

Impact of the Leeuwin Current on the spatial distribution of the puerulus settlement of the western rock lobster (Panulirus cygnus) and implications for the fishery of Western Australia

Previous studies have shown that the strength of the Leeuwin Current is correlated with the level of the puerulus (post-larval stage) settlement in the western rock lobster ( Panulirus cygnus ). The level of puerulus settlement has also been shown to be a reliable predictor of catch in the rock lobster fishery in Western Australia, 3 and 4 yr later. This study examines the impact of the south-flowing Leeuwin Current on the spatial distribution of the puerulus settlement along the coast based on information from 10 settlement sites. In years of strong Leeuwin Current, the location of the peak settlement occurs further south by up to 2° latitude compared with years of weak Leeuwin Current. The key months of Leeuwin Current strength that affect the abundance of the puerulus settlement are generally February to April, during the early larval stages. However, the months that affect the spatial distribution are from June onwards, which is closer to the period of puerulus settlement that starts in about August each year. The mean latitude of puerulus settlement shows a very good relationship with Leeuwin Current strength in June to December ( r  = 0.86, P  < 0.001). The variation in spatial distribution in puerulus settlement can be used to predict the spatial distribution of fishing effort and catch, 3 and 4 yr later ( r  = 0.78 and 0.84, respectively, P  < 0.001).     

饥饿及恢复投喂对刺参生长、耗氧率和排氨率的影响

在水温(16±1)℃、盐度27.6±0.5、pH值7.5~8.3条件下,将体重为(28.47±2.02)g的刺参Apostichopus japonicus分别饥饿0(空白对照)、5、10、15和20d(分别记为T0、T5、T10、T15和T20)后再饱食投喂至40d。实验结果表明,随着饥饿时间的延长,刺参的耗氧率呈急速下降、上升、再下降的变化规律;排氨率呈先上升、后下降的变化规律;氧氮比呈先下降、后上升的变化规律。饥饿结束时刺参的体重,除T5组外,其余各组均显著小于T0组(P0.05),且各自均有不同程度的下降,耗氧率和排氨率与T0组比较均呈显著性差异(P0.05)。饥饿对刺参O/N比值的影响显著(P0.05),饥饿初期刺参O/N比值平均为10左右,随着饥饿时间的延长,刺参O/N比值降为小于7。实验结束时,各饥饿组刺参的体重和特定生长率均小于T0组(P0.05),除T5组外,各组的耗氧率和排氨率,均未能恢复至T0组水平(P0.05)。可见,饥饿后恢复投喂的刺参不具有补偿生长的特征。     

Effects of body weight, water temperature and ration size on ammonia excretion by the areolated grouper (Epinephelus areolatus) and mangrove snapper (Lutjanus argentimaculatus)

The effects of body weight, water temperature and ration size on ammonia excretion rates of the areolated grouper Epinephelus areolatus and the mangrove snapper Lutjanus argentimaculatus were investigated. Under given experimental conditions, L. argentimaculatus had a higher weight-specific ammonia excretion rate than E. areolatus. Weight-specific ammonia excretion rates of fasted individuals of both species showed an inverse relationship with body weight (W, g wet wt.), but a positive relationship with water temperature (t, °C). The relationships for total ammonia nitrogen (TAN) were: E. areolatus: TAN (mg N kg⁻¹ d⁻¹)=21.4·exp^0.11t·W^−0.43 (r²=0.919, n=60); L. argentimaculatus: TAN (mg N kg⁻¹ d⁻¹)=121.5·exp^0.12t·W^−0.55 (r²=0.931, n=60). Following feeding, the weight-specific ammonia excretion rate of E. areolatus increased, peaked at 2 to 12 h (depending on temperature), and returned to pre-feeding levels within 24 h. A similar pattern was observed for L. argentimaculatus, with a peak of TAN excretion being found 6 to 12 h after feeding. Stepwise multiple regression analysis indicated that weight-specific TAN excretion rates of both species increased with increasing temperature and ration (R, percent body wt. d⁻¹): E. areolatus: TAN (mg N kg⁻¹ d⁻¹)=22.8·t−28.8·R−378.2 (r²=0.832, n=24); L. argentimaculatus: TAN (mg N kg⁻¹ d⁻¹)=22.9·t−25.4·R−216.4 (r²=0.611, n=24). The effect of body weight on weight-specific postprandial TAN excretion was not significant in either species (p>0.05). This study provides empirical data for estimating ammonia excretion of these two species under varying conditions. This has application for culture management.     

Biofilm development within a larval rearing tank of the tropical rock lobster, Panulirus ornatus

The role of bacterial biofilms in disease processes is becoming increasingly recognised in both clinical and environmental settings. Biofilm development within a rearing tank of the tropical rock lobster Panulirus ornatus was studied to evaluate if the biofilm is a reservoir for potentially pathogenic bacteria that cause mass larval mortalities. Within a 5000 L larval rearing tank, fiberglass microscope slides were systematically distributed during a standard rearing attempt to assess biofilm development. Culture-based counts for two media types, TCBS and Marine Agar (MA), demonstrated increased bacterial densities until days 11 and 13 respectively. For both media types, a drop in the plate counts was followed by a subsequent increase towards the end of the experiment. Scanning electron microscopy (SEM) confirmed that cell densities decreased between days 13 and 17, most likely due to sloughing of the biofilm into the water column. SEM images revealed distinct changes in dominant morphologies reflecting a succession of bacterial populations. A dynamic succession of microbial species during biofilm development was also demonstrated using denaturing gradient gel electrophoresis (DGGE) profiling of bacterial 16S rRNA genes in combination with statistical ordination analysis. Prominent changes in the DGGE profiles coincided with the decrease in bacterial numbers observed by SEM and plating on MA between days 13 and 17. Fluorescence in situ hybridization (FISH) identified -Proteobacteria as being numerically abundant in the biofilm. This was supported by results from DGGE analysis, which retrieved only sequences affiliated with - and γ-Proteobacteria. DGGE bands affiliated with Vibrio became dominant towards the end of the larval run (days 21 to 24). A Vibrio harveyi strain isolated from the biofilm late in the larval rearing trial (day 24) demonstrated increased larval mortality in small scale phyllosoma survival studies. The detection of Vibrionaceae at the end of the larval trial coincided with mass phyllosoma mortality and show that the biofilm is a reservoir for potentially pathogenic bacteria.     

The effect of environment on puerulus settlement of the western rock lobster (PanuUrus cygnus) in Western Australia

The level of puerulus settlement has proven to be a reliable predictor of the recruitment to the western rock lobster (Panulirus cygnus) fishery three and four years later. It is generally accepted that the early larval stages are moved offshore by wind-driven surface currents. Previous studies have shown that coastal sea level, used as an indicator of the strength of the Leeuwin Current flowing down the west coast of Australia, was positively related to the level of puerulus settling on the inshore reefs after a 9- to 11-month larval life. In this paper a significant relationship is also demonstrated between winter/spring storms, which are usually associated with onshore westerly winds, and the level of puerulus settlement (multiple correlation of 0.83, R¹= 0.68, n = 22). Rainfall from coastal localities was used as an index of the storms. The residuals from this relationship showed a significant positive autocorrelation. The autocorrelation was incorporated into the relationship by using time series analysis with a transfer function model and a first-order autocorrelation (R²= 0.76). The possible relationship between storms and the Leeuwin Current and their effect on the puerulus settlement are considered, and the potential for the environmental variables to bias or obscure the spawning stock recruitment relationship is discussed.     

Effect of body size, photophase, feeding and emersion on the oxygen consumption of the east coast rock lobster Panulirus homarus rubellus

An understanding of the effect of key intrinsic and extrinsic factors on the oxygen consumption of Panulirus homarus rubellus is imperative for the development of optimized transport, holding and growout protocols. This study investigated the effect of body weight, photophase, feeding and emersion on the oxygen consumption rate of P. h. rubellus . Body weight was positively correlated to both standard and active oxygen consumption (mg O₂ h⁻¹) while body weight was negatively correlated to mass-specific standard oxygen uptake (mg O₂ g⁻¹ h⁻¹). Diurnal rhythm exhibited a strong effect on the lobsters' oxygen consumption, with average nighttime values 67% greater than those recorded during the day. This was related to activity driven by intrinsic nocturnal foraging behaviour. Feeding resulted in a classic specific dynamic action response, with postprandial oxygen consumption increasing to a peak before decreasing gradually to preprandial levels. Emersion caused a significant increase in oxygen consumption following re-immersion. Lobsters rapidly recovered to pre-emersion levels after 4 h following a 1-h emersion and after 13.3 h following an emersion period of 6 h. The implications of these results with regard to the holding/culture system and protocol design are discussed.     

Effect of light on oxygen consumption and ammonia excretion in Haliotis discus discus, H. gigantea, H. madaka and their hybrids

Oxygen consumption and ammonia excretion rates of three abalone species, Haliotis discus discus, H. gigantea, H. madaka and their hybrids were measured at 20 °C by incubating for 3 h under dark and light (N = 9–13 for each species and hybrid). Animals were fasted before and during the experiment and measurements were made first under dark followed by light on the next day. The rates increased with the increase in body weight and were higher under light than dark. On average, H. discus discus had higher oxygen consumption (DD; dark = 0.039, light = 0.04 ml/g/h) than H. gigantea (G; D = 0.033, L = 0.036) and H. madaka (M; D = 0.034, L = 0.035); the hybrids had varied patterns with respect to their parental species [DD × M (D = 0.032, L = 0.038); M × DD (D = 0.03, L = 0.038); G × DD (D = 0.035, L = 0.04) and DD × G (D = 0.03, L = 0.034), mother first]. M (0.261, 0.298 μmol/g/h) had the highest ammonia excretion rate while G (0.162; 0.264) and DD (0.229; 0.232) had the lowest under dark and light, respectively. The hybrids had varied patterns in comparison with their parents (DD × M = 0.247, 0.32;M × DD= 0.177, 0.28; DD × G = 0.249, 0.364 and G × DD = 0.116, 0.155). The O/N ratios under both conditions in all species and hybrids indicated that they had carbohydrate dominated metabolism. Results demonstrated physiological variability among the species and hybrids indicating necessity of different strategies for their management and aquaculture.     

Effect of ammonia on the growth rate and oxygen consumption of juvenile greenlip abalone, Haliotis laevigata Donovan

Juvenile greenlip abalone, Haliotis laevigata, (mean whole weight 4.48±1.9 g, mean±s.d., n=953) were highly sensitive to ammonia as indicated by depressed growth rate and food consumption measured over 2–3 months in bioassay tanks. For growth rate expressed on a whole weight basis, the EC₅ and EC₅₀ values (5 and 50% growth reductions) were 0.041 mg FAN l⁻¹ (Free Ammonia–Nitrogen) and 0.158 mg FAN l⁻¹, respectively. Shell growth rates declined over the entire experimental range (0.006–0.188 mg FAN l⁻¹). At the end of the bioassay, groups of abalone were transferred to respiratory chambers. Oxygen consumption rate increased to a maximum of 188% of control values at 0.235 mg FAN l⁻¹ and decreased slightly at the highest concentration of 0.418 mg FAN l⁻¹.     

pH、盐度和温度对海蜇耗氧率和排氨率的影响

为探究环境因子对海蜇耗氧率(oxygen consumption rate,OCR)和排氨率(ammonia excretion rate,AER)的影响,实验通过室内培养,测定了不同pH值、盐度和温度条件下,海蜇幼蜇和成蜇的OCR和AER的变化特征。结果显示,海蜇伞径与干重可用W=0.002 2e^0.1248D表示,R²=0.972 4。海蜇幼蜇和成蜇的OCR和AER受pH值、盐度和温度影响显著。海蜇幼蜇和成蜇的AER和OCR随pH值的升高呈现先增大后减小的趋势,幼蜇和成蜇的2种代谢率分别在pH值为7.0和7.5时达到最大值,同时收缩次数最多。海蜇幼蜇和成蜇的AER和OCR随盐度的升高呈现先增后减的趋势,分别在盐度为25和20时达到峰值;盐度为20时收缩力最强。不同规格海蜇的OCR随温度升高而增加;AER则随温度升高呈先增大后减小的趋势,25°C达到峰值。海蜇在21°C时运动和进食最快,温度低于3°C或高于35°C海蜇则停止运动。幼蜇的AER Q₁₀值为0.767～4.362,OCR Q₁₀值为1...     

温度和盐度对红刺参(Apostichopus japonicus)耗氧率与排氨率的影响

采用室内实验生态学方法,研究了不同温度(7、12、17、22、27℃)、盐度(23、26、29、32、35、38)对两种体重S组(1.68–3.48 g)和L组(15.78–20.79 g)红刺参(Apostichopus japonicus)耗氧率(OCR)和排氨率(AER)的影响。结果显示,温度对红刺参OCR和AER均有极显著影响(P<0.01);体重对红刺参OCR无显著影响(P>0.05),而对AER有极显著影响(P<0.01)。温度和体重交互作用对红刺参OCR和AER有极显著影响(P<0.01)。S组红刺参的OCR和AER随温度的升高而增加;L组红刺参OCR和AER均随温度的升高而升高,而在22℃有所降低后又升高。盐度、体重对红刺参OCR和AER均有显著影响(P<0.05)。盐度和体重交互作用对红刺参OCR和AER均无显著影响(P>0.05)。S组和L组红刺参的OCR和AER均随盐度的升高而呈M形变化,在盐度为29和32时较低,而在盐度为26和35时较高。红刺参OCR和AER与体重呈负相关的幂函数方程R = aW b。不同温度下S组和L组红刺参O : N范围分别为4.75–11.74和10.71–15.52;不同盐度S组和L组红刺参O : N范围分别为6.37–12.29和8.24–12.10。综上所述,L组红刺参对高温的耐受能力较S组弱;S组和L组红刺参对低盐和高盐的耐受性较差,其最适盐度范围为29–32。     

北部湾鲔(Euthynnus affinis)的摄食习性及其随生长发育的变化

基于2008年9月-2009年9月在北部湾逐月采集的435尾鲔(Euthynnus affinis)生物学数据,对鲔生长、摄食习性及其随生长发育的变化进行了分析。结果显示,北部湾鲔属于广食性鱼类,主要摄食中上层小型鱼类,另外还包括底栖鱼类、甲壳类和头足类等。少鳞犀鳕(Bregmaceros rarisquamosus,45.50%)、青带小公鱼(Stolephorus zollingeri,11.81%)和长颌棱鳀(Theyssa setirostris,5.89%)为鲔优势饵料生物种类,并且其主要饵料生物种类随采样时间的不同而有所差异,如金色小沙丁鱼(Sardinella aurita,1月)、未能鉴定鱼类(4-7月)、长颌棱鳀(8月)、条鲾(Leignathus riviulatus,9月)、青带小公鱼(10月)、少鳞犀鳕(11–翌年3月)。体长小于340 mm的鲔个体随体长的增加其平均摄食饵料生物的个数与质量呈上升趋势;体长在341-520 mm范围内的鲔个体,随着体长的增加其平均摄食饵料生物的个数与质量总体上呈现下降趋势。鲔产卵主要集中在4-8月,根据雌性GSI(性腺成熟度指数)分析,具有两个产卵高峰期(6月、8月),产卵高峰期和中上层水温的升高有密切关系。鲔的摄食强度在性腺发育过程中波动较大,但在产卵期间,其摄食强度并未明显降低。     

Effects of pond preparation and feeding rate on production of Penaeus monodon Fabricius, water quality, bacteria and benthos in model farming ponds

Fibreglass pools with sediment were used as model farming ponds to investigate the interactive effects of pond preparation and feeding rate on prawn production, water quality, bacterial dynamics, abundance of benthos and prawn feeding behaviour. Pools were either fertilised 1 month (prepared) or 2 days (unprepared) prior to stocking and either ‘high’ or ‘low’ feeding rates were used. The ‘high’ rate was 5.0% (range 4–8%) wet prawn biomass/day and was similar to that recommended for commercial farms. The ‘low’ rate was 2.5% (range 2–4%) wet prawn biomass/day. Juvenile Penaeus monodon (2.0–7.5 g) were stocked at 15 prawns/m² and were cultured for 71 days. With the exception of one prepared, high feeding-rate pool where mass mortality (> 80%) of prawns occurred following an interruption to aeration, prawn survival was high (> 86%) and was unaffected by preparation, feeding rate or their interaction. Pond preparation improved growth and biomass gain by about 20%. Growth was 4% higher with the higher feeding rate but biomass gain was not affected and, as food conversion ratio was much worse, use of the lower feeding rate offers considerable scope to reduce production costs, especially during cooler periods. There was no interaction in relation to growth between pond preparation and feeding rate. Meiofauna were more abundant, and prawns grew faster, in prepared pools than unprepared pools at the start of the experiment. However, changes in bacterial dynamics or meiofauna abundance over time did not explain reductions in prawn growth over time. In general, water quality was reduced in pools receiving the high feeding rate compared with low feeding rate pools. Other interactive effects of pond preparation and feeding rate on water quality, bacteria, benthos and prawn feeding behaviour are discussed.     

水产品鲜活品质评价体系研究进展

探究虾夷扇贝 (Patinopecten yessoensis) 保活运输前的最佳诱导休眠方式,可为其保活流通提供理论依据。参考产业实际流通,采用散冰降温和急性降温和梯度降温3种低温诱导休眠方式处理虾夷扇贝,探讨了不同降温休眠方式对虾夷扇贝无水保活期的成活率、生命特征及营养品质的影响。结果表明：梯度降温组在4 ℃条件下保活3 d后的成活率为93.33%,明显高于急性降温和散冰降温组;在降温休眠过程中,散冰降温和急性降温组由于温度骤变,无法检测到规律的心电图,梯度降温组的心率呈规律性缓慢下降趋势;保活期间,各组扇贝的心率均呈下降趋势,保活3 d后,散冰降温组已无规律心率,梯度降温和急性降温组仍有规律心率;3组降温方式的缩边率和外套膜响应时间均呈逐渐上升的趋势,其中散冰降温和急性降温组的缩边率和外套膜响应时间显著高于梯度降温组,且心率与外套膜响应时间呈负相关关系;水分、粗蛋白、粗脂肪和肌糖原含量均呈下降趋势,其中对肌糖原的消耗最大,梯度降温组相较于其他组在保活期营养成分损失较少,且梯度降温组的闭壳肌在微观组织结构上排列紧密整齐,无明显断裂。研究表明,采用梯度降温诱导扇贝进入休眠或半休眠状态后开始无水保活,有利于提高活体扇贝的成活率,减少其在流通过程中营养成分的损失,进而保持其活力,更有利于其无水保活。     

The effect of plant protein‐based diets on apparent nutrient digestibility,growth response,egesta quantity,postprandial ammonia excretion rate and serum quality of Nile tilapia

The study assessed the effect of oilseed meal mixtures on the biological value, faecal matter output, ammonia excretion rates and serum biochemistry of Nile tilapia over 63 days. The experimental diets (PPB 1, PPB 2 and PPB 3) were formulated using four selected oilseed meals that were mixed in different protein proportions to contribute 80% of total dietary crude protein. In each diet, either one or two of the oilseed meals were the dominant protein contributor. A commercial tilapia feed was used as the control diet (CTRL). Sex‐reversed Nile tilapia fingerlings (35 g) were stocked at 20 fish per tank in a recirculation system and fed at 3% body weight of their respective diets. At the end of the study, ADCs of dry matter, crude lipid and ash were significantly (p < .05) lower in all the plant‐based diets compared with the control diet. Fish fed the control diet had significantly higher weight gain and SGR compared with the plant‐based diets. Egesta output was 127% higher in the plant‐based diets compared with the control diet. All dietary treatments exhibited a similar trend in changes in ammonia nitrogen. Nevertheless, serum metabolites levels indicated no significant differences among treatments. Although the PPBs did not affect ADC of protein and serum profile, fish growth was reduced while faecal output increased.     

The effect of freezing on the length and weight measurements of ruffe (Gymnocephalus cernuus)

The ruffe is a percid native to Europe and Asia that has invaded several new areas in the last several decades. For population studies ruffe are often frozen en masse after collection in the field and thawed at a later time for measurements of length and weight. I determined the effect of freezing and thawing on ruffe total length (TL) and weight (W) by making these measurements on freshly caught ruffe and ruffe that had been frozen and thawed. Frozen and thawed fish generally shrank by between 1.25% and 1.63% (95% CI) of their fresh TL and approximately 5–10% of their fresh W. Shrinkage in W increased as the length of time being frozen increased. The log_e(W)– log_e(TL) relationship differed between fresh and thawed ruffe. Relative underestimation of actual fresh W using thawed TL and a log_e(W)– log_e(TL) relationship constructed from thawed fish was 7.50%. All observed shrinkage amounts were substantially different than within-technician measurement variability. These results suggest that fresh specimens should be used if it is important to understand the true fresh measurements of ruffe. In the absence of being able to do this, (provided) corrections for errors due to thawing should be used.