Differences in the total lipid and lipid class composition of larvae and metamorphosing sea lampreys, Petromyzon marinus

This study compared the alterations in total lipid and lipid class composition of kidney, liver, and intestine from sea lamprey, Petromyzon marinus, during their nontrophic metamorphosis with these parameters in unmetamorphosed larvae. Total lipid in kidney and liver initially was higher by 104 and 66%, respectively, in the earliest metamorphic stage (3) examined compared to larvae and then decreased by 73 and 37%, respectively, from stage 3 to stage 7. Total lipid in intestine, on the other hand, was 53% lower at stage 3 compared to larvae and then significantly increased by 260% from stage 3 to stage 7. Large amounts of triacylglycerol (TG) in kidney and liver implicate these organs as lipid depots; much of the change in total lipid content of kidney and liver could be explained by alterations in TG, although significant variations in other lipid classes (e.g., phospholipid, cholesterol) also were noted. These results suggest that lamprey metamorphosis may proceed in two metabolic phases in a tissue-specific manner and that lipid depletion results from specific catabolism of stored TG reserves.     

Late winter larval mesopelagic fish assemblage in the Kuroshio waters of the western North Pacific

The larval mesopelagic fish assemblage and its distribution patterns were investigated in the Kuroshio region off southern Japan in late winter. A total of 8690 fish larvae was collected, 85.8% of which were mesopelagic fish larvae. Mesopelagic fish larvae were significantly more abundant in the area east of the Kuroshio axis than west of the Kuroshio axis (660.6 versus 194.5 ind 10 m^?2). Sigmops gracile, Bathylagus ochotensis, Notoscopelus japonicus, Diaphus slender type and Myctophum asperum were the five most abundant larvae and accounted for 16.9, 16.4, 15.2, 13.9 and 9.3% of the total catch in numbers, respectively. We conclude that these larvae were transported by the Kuroshio Current to the more productive transition waters, where they spend their juvenile stage from spring to early summer. The possibility of expatriation and southward long‐distance spawning migrations of N. japonicus and B. ochotensis are discussed, based on the geographic distribution patterns of their larvae, juveniles and adults.     

Spatial and temporal distribution and abundance of European hake, Merluccius merluccius, eggs and larvae in the Catalan coast (NW Mediterranean)

Plankton hauls were conducted on five surveys from November 1998 to November 1999 to study the spatial distribution of eggs and larvae of European hake off Catalonia (NW Mediterranean Sea). Also CTD casts to record hydrographic parameters were carried out on a closely spaced station grid. Merluccius merluccius eggs and larvae appeared mainly in late spring, summer and autumn surveys and were very scarce in winter. Strong differences in terms of egg and larval densities were observed between the two November surveys, which could be attributed to the anomalous hydrographic situation during November 1998. M. merluccius egg and larvae were mainly distributed over the continental shelf, with peak abundances between the 100 m isobath and the edge of the shelf. On the evidence of larval size frequency distributions in the different sampling sectors and the closely overlapping distribution patterns for the eggs and the adult spawning stock, drifting of hake eggs and larvae was not a major factor. The larval distribution extended only slightly further offshore than the egg distribution. Using the hydrographic information and the larval distribution data, an attempt was made to relate the different seasonal productivity levels over the spawning period and the distribution of the larvae.     

Development of microparticle diets for Japanese flounder Paralichthys olivaceus larvae

ABSTRACT:   Two newly designed microparticle diets (MD), with two kinds of peptide (C700 and C800) as a protein source were developed. Microparticle diet Q (MD-Q) contained C700 (molecular weight ∼30 000 Da) and C800 (molecular weight 1000–2000 Da); in contrast, microparticle diet T (MD-T) contained C700 only. Two separate trials, representing larvae from different hatches, were conducted. Japanese flounder Paralichthys olivaceus larvae were fed newly designed MD or a combination of them with live food (LF) between 3 and 10 days after hatching (d.a.h.) in experiment I, or between 11 and 20 d.a.h. in experiment II, and compared them to LF and a commercial diet (CD) feeding groups. The growth and survival rates in both experiments were the highest in the LF treatment. But in the microparticle treatment larvae fed MD-Q had a higher survival rate and better growth than those fed MD-T, either alone or in combination with LF. First-feeding larvae fed on MD-Q had a 20.5% survival rate and 1.12 mm gain by 10 d.a.h. Unfed larvae died within 6 d.a.h. These results indicate that using a mixture of different molecular weight peptides is good protein sources and also this type of microparticle diet can be applied to flounder from larval to juvenile stages.     

鳀鱼仔鱼饥饿试验及不可逆点的确定

2000年6月26日8-10时在35°00′N、121°00′E周围海域利用大型浮游生物网采集了大量鳀鱼的天然受精卵,11时受精卵开始孵化,12时收集初孵仔鱼进行饥饿试验。试验结果表明:在培养水温为23.0～24.8℃条件下,鳀鱼仔鱼的混合营养期仅1d多时间;仔鱼的不可逆点发生在孵化后第6天。鳀鱼后期仔鱼发育阶段都具有胸角这一形态特征,其胸角不能作为鉴别健康仔鱼和饥饿仔鱼的依据。这一发现补充和完善了鱼类学上关于仔鱼胸角的理论。     

The effect of tank colouration on survival, metamorphosis rate, growth and time to metamorphosis freshwater prawn (Macrobrachium rosenbergii) rearing

Seedstock‐costs of the freshwater prawn Macrobrachium rosenbergii can represent >50% of the total production costs. The purpose of this study was to evaluate the effect of culture tank colouration on survival, metamorphosis rate, weight and time required to reach the postlarval (PL) stage. Newly hatched prawn larvae were stocked into eighteen 16‐L plastic culture tanks at a density of 30 L^?1. Tank colours evaluated were red, black, white, blue, green and yellow. Larval prawns were fed brine shrimp (Artemia franciscana) nauplii and a supplemental diet. Data indicated that larval tank colour had no significant impact (P>0.05) on the final PL size or days required to reach PL stage. However, total survival was significantly higher (P<0.05) in red and green tanks (84% and 78% respectively) than in white and blue tanks (56% and 44% respectively). Survival in the yellow and black tanks (71% in both) was not significantly different (P>0.05) from the red, green or white treatments, but was significantly higher (P<0.05) than the blue treatment. This could have a significant financial impact on commercial hatchery, and growout production, as most larval tanks currently in use are blue or black.     

Ontogenetic diet shifts in a neotropical catfish, Sorubim lima (Schneider) from the River Paraná System

This study examines the diet of Sorubim lima (Schneider) during its early life stages and compares it with available food resources. Prey species preference was estimated by computing the Strauss index. The diet was diverse, and rotifers and cladocerans were the most important items. Pre-flexion larvae ate rotifers and cladocerans. Around flexion, cladocerans were dominant and the ingestion of fish also began. As larvae grew, the percentage of rotifers diminished. In post-flexion larvae, cladocerans were also dominant, and the ingestion of insects and fish was more frequent. The Strauss index showed negative selection for rotifers, positive values for cladocerans and neutral for copepods. The role of the lotic habitats as nursery areas for fish larvae was discussed.     

Effects of acute and chronic toxicity of unionized ammonia on mud crab, Scylla serrata (Forsskål, 1755) larvae

While the effects of ammonia on fish and prawn larvae are well documented, little is known of its effect on mud crab (Scylla serrata) (Forsskål, 1755) larvae. Two experiments were conducted in 5 L hemispherical plastic bowls, containing 3 L of ultra‐filtered and settled seawater and various larval stages of mud crab to (1) determine the acute median lethal concentration (LC₅₀) of unionized ammonia and (2) to determine the chronic effects of unionized ammonia on survival and percentage moulting to zoea and megalop stages. The larval stages that exhibited the highest tolerance to ammonia over 24 h were zoea 1 (LC₅₀ of 4.05 mg L^?1 of unionized ammonia) and zoea 5 (LC₅₀ of 6.64 mg L^?1 of unionized ammonia). The megalop stage had the lowest total ammonia LC₅₀ at both 24 and 48 h, making it the larval stage most susceptible to total ammonia. Exposure to 6.54 mg L^?1 of unionized ammonia resulted in 100% death of all larvae within 24 h. The tolerance of S. serrata larvae to total ammonia did not appear to increase with ontogenetic development. The results indicate that the concentrations at which total ammonia produces an acute or chronic response in mud crab larvae are far higher than those experienced in current larval production systems (0–0.5 mg L^?1 of total ammonia) used as industry standards in Australia.     

Urea and ammonia excretion by embryos and larvae of the African catfish Clarias gariepinus (Burchell 1822)

Yolk-sac larvae and starved larvae of Clarias gariepinus (Burchell 1822), reared at 28°C, were predominantly ammonotelic, but urea excretion contributed about 19±7% to the total nitrogen excretion. Exogenously feeding larvae of C. gariepinus were mainly ammonotelic until 180-205 h post fertilization, but from then on the relative urea excretion stabilized at 44±13%. The contents of total free amino acids (FAA) and ammonia in C. gariepinus peaked around complete yolk absorption. During the first period after hatching 64% of the FAA and 60% of the total ammonia were located in the yolk compartment. The body compartment contained the highest amount of FAA and total ammonia at the end of the yolk-sac period (65 and 77%, respectively). The amount of nitrogen originating from catabolism of amino acids was balanced within 6% by the excreted sum of ammonia and urea. The high degree of ureotelism in C. gariepinus larvae may constitute an adaptive mechanism to a habitat of temporal water shortage.     

饵料卤虫的营养强化对黑斑口虾蛄(Oratosquilla kempi) 幼体消化酶活力及其抗逆性的影响

用扁藻、酵母和"鱼油 酵母"强化3种方式处理的卤虫无节幼体投喂黑斑口虾蛄幼体,对各组黑斑口虾蛄幼体消化酶活力和抗逆性差别分析。结果显示,经过"鱼油 酵母"强化的幼体对氨氮、福尔马林、饥饿和盐度的耐受性均强于对照组。经过扁藻和"鱼油 酵母"强化的第Ⅲ相幼体脂肪酶活力是对照组的3倍,经过酵母和"鱼油 酵母"强化的仔虾蛄幼体脂肪酶活力较高。在第Ⅲ相幼体中淀粉酶活力为扁藻>酵母>对照>"鱼油 酵母"强化,仔虾蛄中酶活力为扁藻>对照>酵母>"鱼油 酵母"强化。在酵母强化第Ⅲ相幼体和对照组仔虾蛄中纤维素酶活力最高。第Ⅲ相幼体对照组的胃蛋白酶和类胰蛋白酶活力均为最高,而"鱼油 酵母"强化仔虾蛄幼体的胃蛋白酶和类胰蛋白酶活力均高于对照组。黑斑口虾蛄幼体消化酶活性和抗逆性能力的变化趋势与其成活率、变态率、生长速度、EPA和DHA含量变化趋势相同,可以作为评价饵料质量好坏的重要指标。