Reproductive biology of albacore Thunnus alalunga

Reproductive variables in albacore Thunnus alalunga were evaluated by gonad histology in samples of 132 males (58–118 cm fork length, L_F) and 112 females (59–101 cm L_F) that were collected from the western North Pacific Ocean from 2001 to 2006. In the sex ratio examination, males greatly outnumbered females in large adult fish (L_F > 100 cm). Thunnus alalunga exhibited a protracted spawning period from March to September in the waters off eastern Taiwan and the Philippines, and the peak spawning activity occurred in March and April. Minimum sizes associated with the classification of mature fish were 78 and 83 cm L_F for males and females, respectively. In addition, the largest L_F of immature fish were 93 cm for males and 94 cm for females. The spawning frequency estimate in April was 1·7 days. Batch‐fecundity estimates of 21 females (89–99 cm L_F) ranged between 0·17 and 1·66 million eggs (mean ±s.d . = 0·94 ± 0·43). The relative fecundity estimates of the 21 females ranged between 9·2 and 92·4 oocytes g^?1 body mass (mean ±s.d . = 50·5 ± 22·8). The results presented in this study provide increased information regarding this species' reproductive‐related characteristics than are currently available in stock status determinations.     

Spatial and sex-specific variation in growth of albacore tuna (Thunnus alalunga) across the South Pacific Ocean

Spatial variation in growth is a common feature of demersal fish populations which often exist as discrete adult sub-populations linked by a pelagic larval stage. However, it remains unclear whether variation in growth occurs at similar spatial scales for populations of highly migratory pelagic species, such as tuna. We examined spatial variation in growth of albacore Thunnus alalunga across 90° of longitude in the South Pacific Ocean from the east coast of Australia to the Pitcairn Islands. Using length-at-age data from a validated ageing method we found evidence for significant variation in length-at-age and growth parameters (L(∞) and k) between sexes and across longitudes. Growth trajectories were similar between sexes up until four years of age, after which the length-at-age for males was, on average, greater than that for females. Males reached an average maximum size more than 8 cm larger than females. Length-at-age and growth parameters were consistently greater at more easterly longitudes than at westerly longitudes for both females and males. Our results provide strong evidence that finer spatial structure exists within the South Pacific albacore stock and raises the question of whether the scale of their "highly migratory" nature should be re-assessed. Future stock assessment models for South Pacific albacore should consider sex-specific growth curves and spatial variation in growth within the stock.     

Indications of strong adaptive population genetic structure in albacore tuna (Thunnus alalunga) in the southwest and central Pacific Ocean

Albacore tuna (Thunnus alalunga) has a distinctly complex life history in which juveniles and adults separate geographically but at times inhabit the same spaces sequentially. The species also migrates long distances and presumably experiences varied regimes of physical stress over a lifetime. There are, therefore, many opportunities for population structure to arise based on stochastic differences or environmental factors that promote local adaptation. However, with the extent of mobility consistently demonstrated by tagged individuals, there is also a strong argument for panmixia within an ocean basin. It is important to confirm such assumptions from a population genetics standpoint for this species in particular because albacore is one of the principal market tuna species that sustains massive global fisheries and yet is also a slow‐growing temperate tuna. Consequently, we used 1,837 neutral SNP loci and 89 loci under potential selection to analyze population genetic structure among five sample groups collected from the western and central South Pacific. We found no evidence to challenge panmixia at neutral loci, but strong indications of structuring at adaptive loci. One population sample, from French Polynesia in 2004, was particularly differentiated. Unfortunately, the current study cannot infer whether the divergence is geographic or temporal, or possibly caused by sample distribution. We encourage future studies to include potentially adaptive loci and to continue fine‐scale observations within an ocean basin, and not to assume genome‐wide panmixia.     

南太平洋长鳍金枪鱼渔场CPUE时空分布及其与关键海洋环境因子的关系

根据2009—2012年南太平洋长鳍金枪鱼(Thunnus alalunga)延绳钓生产统计数据及遥感获取的海表温度(sea surface temperature,SST)、叶绿素a浓度(chlorophyll a concentration,Chl-a)和海面高度距平(sea surface height anomaly,SSHA)等环境数据,分析了长鳍金枪鱼单位捕捞努力量渔获量(catch per unit of fishing effort,CPUE)的时空分布及其与环境因子的相关性。结果表明:长鳍金枪鱼作业渔场主要集中在4°S—28°S、158°E—176°E附近海域;长鳍金枪鱼渔场CPUE呈明显的季节性变化,1—3月CPUE值较低(12.5尾·千钩-1),随后逐渐增加,至7月达到最大值为18.1尾·千钩-1,而8—12月基本呈逐渐降低趋势;1月渔场重心位于16°S、168°E附近海域,2—3月向西北偏移,而在3—7月逐渐向东南方向转移,8月以后开始逐渐回撤至西北方向,在9—12月渔场重心变化幅度相对较小,主要位于15°S—16°S、168°E—169°E海域;总体来说,长鳍金枪鱼中心渔场最适SST为27.0~30.5℃,次适SST为20~24℃;最适叶绿素a浓度为0.02~0.08mg·m-3,最适海面高度距平为3~23 cm。     

The potential use of scales for estimating age and growth of Mediterranean albacore (Thunnus alalunga)

The ability to accurately estimate the age of fishes is critical for conducting stock assessments and developing fishery management policies. Scales were collected from albacore, Thunnus alalunga, caught in the Mediterranean Sea during the years 1989–1995 to estimate their age and growth. Ages, which ranged from 1+ to 6+ years, were estimated from the interpretation of the concentric rings on the scales of 473 individuals that ranged in fork length from 55.5 to 89 cm. Males reached a greater size and age than females. The relatively close agreement in the mean lengths at ages estimated by scales and other techniques constituted a preliminary verification of the method. The von Bertalanffy growth model was fitted to mean lengths at estimated ages, resulting in the following growth parameters for the combined sexes: L_∞ = 86 cm, K = 0.4, t_o = ?0.8 years. Parameter estimates were in agreement with what is known about life history of the species in the Mediterranean. Moreover, the growth rates were consistent with length increment observations from five tag returns, which lend support to our working hypothesis that the scale‐rings are annual structures. When the Mediterranean albacore growth parameters were compared with those of Atlantic Ocean albacore using scale age estimates, there were significant differences between the two populations, and Mediterranean albacore remain significantly smaller than Atlantic Ocean albacore.     

Haematological characteristics of albacore, Thunnus alalunga (Bonnaterre), and skipjack, Katsuwonus pelamis (Linnaeus)

Observations on haematological characteristics of albacore, Thunnus alalunga , and skipjack Katsuwonus pelamis , tunas, were made on blood samples collected from specimens immediately after they were caught and from an immobilized, restrained albacore sampled serially over a 24 h period. Results indicated eight types of blood cells in the peripheral circulation of both species. Lymphocytes were the most common leucocyte followed, in decreasing order, by neutrophils, eosinophils and monocytes in fish sampled immediately after being landed. Variations in differential and total white blood cell counts were observed in the immobilized, restrained albacore. High packed cell volumes and haemoglobin concentrations, typical for fast swimming fishes, were found in both species. Red blood cell counts were similar to those of other teleosts, and reticulocytes expressed as a percentage of mature erythrocytes were 6.1% and 5.2% for albacore and skipjack, respectively.     

Age and growth of albacore Thunnus alalunga in the North Pacific Ocean

The age and growth of North Pacific albacore Thunnus alalunga were investigated using obliquely sectioned sagittal otoliths from samples of 126 females and 148 males. Otolith edge analysis indicated that the identified annulus in a sagittal otolith is primarily formed during the period from September to February. The assessments of the fish age at first annulus formation indicated that the first annulus represents an age of <1 year. This study presents an age estimate (0·75 years) for the formation of the first annulus. The oldest fish ages observed in this study were 10 years for females and 14 years for males. The von Bertalanffy growth parameters of females estimated were L(∞) = 103·5 cm in fork length (L(F) ), K = 0·340 year(-1) and t(0) = -0·53 years, and the parameters of males were L(∞) = 114·0 cm, K = 0·253 year(-1) and t(0) = -1·01 years. Sexual size dimorphism between males and females seemed to occur after reaching sexual maturity. The coefficients of the power function for expressing the L(F) -mass relationship obtained from sex-pooled data were a = 2·964 × 10(-5) and b = 2·928.     

Partitioning of caseinomacropeptide in aqueous two-phase systems

This study evaluates the influence of type of salt and temperature on the partition coefficient of caseinomacropetide (CMP) to determine the best conditions for the recovery of CMP in aqueous two-phase systems (ATPS) composed by poly(ethylene glycol) (PEG) 1500 and an inorganic salt (potassium phosphate, sodium citrate, lithium sulfate or sodium sulfate). In all systems, CMP presented affinity for the PEG-rich phase. The PEG1500+lithium sulfate showed the highest values of partitioning coefficient. In addition, thermodynamic parameters (DeltaH degrees , DeltaS degrees , DeltaG degrees) as a function of temperature, were calculated for the system PEG1500-sodium citrate at different PEG concentrations and the results imply thermodynamic differences between partitioning of CMP in this system.     

Partitioning of glycomacropeptide in aqueous two-phase systems

The partition behavior of glycomacropeptide (GMP) was determined in polyethylene glycol (PEG) and sodium citrate aqueous two-phase systems (ATPS). It was found that the partitioning of GMP depends on PEG molar mass, tie line length, pH, NaCl concentration and temperature. The obtained data indicates that GMP is preferentially partitioned into the PEG phase without addition of NaCl at pH 8.0. Larger tie line lengths and higher temperatures favor GMP partition to the PEG phase. Furthermore, it was verified that PEG molar mass and concentration have a slight effect on GMP partition. The increase in the molar mass of PEG induces a reduction of the protein solubility in the top PEG rich phase, being shown that the use of PEG1500 is beneficial for the extraction of GMP. A protein recovery higher than 85% was obtained in the top phase of these systems, clearly demonstrating its suitability as a starting point for the separation of GMP.     

Cumulative effect of the North Atlantic Oscillation on age‐class abundance of albacore (Thunnus alalunga)

The aim of this study was to look into possible relationships between climate and the inter‐annual variability of albacore (Thunnus alalunga) catch rates by age class observed during a recreational fishery tournament at the spawning grounds of S’Estanyol (Balearic Islands, Spain) in the years 2004–2009. The mean capture per unit effort (CPUE) was significantly higher when the mean of the North Atlantic Oscillation (NAO) experienced by the albacore in winter and spring of its life history (NAO_life) was negative than when the NAO_life was positive. A statistically significant negative relationship was obtained between NAO_life and the probability of a CPUE value for an age class and year being higher than the average CPUE for all the cohorts in that age class. The results suggest that local abundance of albacore in a spawning grounds could be related to environmental factors dependent on the NAO and that there may be a cohort‐age effect. It is hypothesized that factors dependent on the NAO, such as the abundance variation of small pelagic fishes as a response to the NAO variability, could have a cumulative effect over the good biological condition (fitness) of a long‐living fish predator such as the albacore.     

Testes development and maturity classification of albacore (Thunnus alalunga ( Bonaterre, 1788)) from the Eastern Mediterranean Sea

The criteria of testicular maturity during the spawning season and for maturity rates are described according to age for 140 male albacore (Thunnus alalunga, Bonnaterre, 1788) sampled between April and August, 2002–2008 in the Eastern Mediterranean Sea. Histology of gonad samples was used to determine maturity status. Spermatogenesis and its relation to reproductive biology are reported. Fish ranged in fork length (FL) from 63 to 90 cm. The reproductive classes were based upon changes in the testicular morphology and stages of the germinative cells, i.e. immature, developing, maturing, spawning, and spent. Mature stages of testes including the smallest sample of a 63 cm male were observed from May to August of each year during the study. The reported evidence indicates that the size and age of first sexual maturity values of males of the Eastern Mediterranean population are nearly the same as in the Western Mediterranean population, but lower than in the Atlantic stock. The results of this histological investigation, conducted for the first time on this species in the Mediterranean Sea, will enable more precise future estimations for sustainability of the male albacore stock in the Eastern Mediterranean.     

Ovarian development of albacore (Thunnus alalunga Bonnaterre, 1788) in the Eastern Mediterranean Sea: a histological characterisation

In order to investigate the stages of oogenesis in the albacore Thunnus alalunga, 129 females (64.0?83.5 cm fork length‐FL) were captured by gill nets from April to August 2002–2008, in the eastern Mediterranean Sea. Based on histological examination of the ovaries, a total of seven ovarian developmental stages were identified: perinucleolar, lipid, early vitellogenesis, late vitellogenesis, migratory nucleus, pre‐hydrated and hydrated. The monthly gonadosomatic index values and the results of the histological analysis indicated that the females mature in May. The spawning stage becomes predominant in June and reaches a maximum in July. The evidence reported here indicates that the size of females at first sexual maturity was lower for the Mediterranean albacore stock than for the Pacific and Atlantic stocks.     

Autoxidation of myoglobin from bigeye tuna fish (Thunnus obesus)

Native oxymyoglobin (MbO2) was isolated directly from the skeletal muscle of bigeye tuna (Thunnus obesus) with complete separation from metmyoglobin (metMb) on a CM-cellulose column. It was examined for its stability properties over a wide range of pH values (pH 5-12) in 0.1 M buffer at 25 degrees C. When compared with sperm whale MbO2 as a reference, the tuna MbO2 was found to be much more susceptible to autoxidation. Kinetic analysis has revealed that the rate constant for a nucleophilic displacement of O2- from MbO2 by an entering water molecule is 10-times higher than the corresponding value for sperm whale MbO2. The magnitude of the circular dichroism of bigeye tuna myoglobin at 222 nm was comparable to that of sperm whale myoglobin, but its hydropathy profile revealed the region corresponding to the distal side of the heme iron to be apparently less hydrophobic. The kinetic simulation also demonstrated that accessibility of the solvent water molecule to the heme pocket is clearly a key factor in the stability properties of the bound dioxygen.     

Partitioning of host and recombinant cells in aqueous two-phase polymer systems

The separation of host and recombinant Escherichia coli bacterial cells has been studied using the surface-sensitive technique of partitioning in aqueous two-phase polymer systems. Experiments were designed to probe charge-and hydrophobicity-related property differences of antibiotic-resistant recombinant cells and their antibiotic-sensitive hosts. Differential partitioning was observed in both charge-sensitive and non-charge-sensitive phase systems for three host-recombinant cell systems, but the non-charge-related effects appear to have a greater impact on partitioning behavior. This result suggests that plasmid-encoded products related to antibiotic resistance modify the surface hydrophobicity of the E. coli bacterial cell and that these differences can be exploited for cell separation.     

Partitioning of acid proteases in aqueous two-phase systems containing a charged polymer

Summary A preparation of DEAE-dextran was described, which can form an aqueous two-phase system with hydroxypropyldextran. Acid proteases showed strong partition in this system due to its large interfacial electrical potential. Partition coefficients of the enzymes changed rapidly when salts were added.     

Partitioning and characterization of tyrosine-tagged green fluorescent proteins in aqueous two-phase systems

The green fluorescent protein GFPuv has been genetically engineered to investigate the influence of N-terminal tyrosine extensions in aqueous two-phase systems. Fusions in the N-terminus affected the protein expression, and tags containing three tyrosines and prolines influenced the expression favorably. This effect is probably due to changes in mRNA stability, because the amounts of corresponding mRNAs correlated with the amounts of GFPuv proteins. The partitioning was investigated in two different aqueous two-phase systems, a two-polymer system composed of EO30PO70/dextran and a PEG/salt system with potassium phosphate. Partitioning in the PEG/salt system generally was more favorable than in the EO30PO70/dextran system. Tags with three tyrosines resulted in higher partitioning toward the EO30PO70- and PEG-rich phases, respectively. The effect of adding proline residues to the tag was also investigated, and the partitioning effect of the tag was enhanced when prolines were included in the tags with three tyrosines. The best tyrosine tag, Y3P2, increased the partition coefficient 5 times in the PEG/salt system. Thermoseparation of the EO30PO70 phase allowed recovery of 83% Y3P2-GFPuv protein in a water phase.     

Partitioning of amylase produced by Aspergillus niger in solid state fermentation using aqueous two-phase systems

Equilibrium data of aqueous two-phase systems composed of polyethylene glycol (4000 g mol⁻¹ or 6000 g mol⁻¹) and Li₂SO_4, (NH₄)₂SO₄ or Na₂SO₄ at pH 6.5 and 25 °C were obtained. The efficiency of these in the partition of amylases derived from Aspergillus niger was determined. The experimental data of binodal curves and tie lines were used to estimate the group interaction parameters using the UNIFAC model. Additionally, the influence of phases on the activity of the enzymes was investigated. The results indicate that the polymer molar mass did not influence the biphasic region size. However, the cations under study presented differences in induction to phase formation. It was verified that the systems formed with the Na⁺ presented a larger biphasic region. The increase in the molar mass of the polymer caused the increase in the exclusion volume from 3970.732 g mol⁻¹ to 5700.873 g mol⁻¹. The transfer Gibbs free energy of enzymes presented values between −1296.30 kJ mol⁻¹ and −2867.70 kJ mol⁻¹, that is, the process was spontaneous for all systems studied. The systems formed by (NH₄)₂SO₄ and PEG 4000 g mol⁻¹ presented the best K_e result (3.421) and theoretical recovery of 80.35 %.     

A unique selenoprotein isolated from yellowfin tuna (Thunnus albacares) liver

A selenoprotein, with an approximate molecular weight of 2000, was isolated from yellowfin tuna (Thunnus albacares) liver. The selenium (Se) content of this selenoprotein fraction represented greater than 50% of the Se in the original liver extract. Most of the unrecovered Se was left in the pellet following homogenization. Although the protein was very sensitive to oxidizing conditions, it remained stable in the presence of reducing agents such as glutathione and dithiothreitol under a nitrogen atmosphere. After preparative isoelectric focusing of the purified selenoprotein, selenium was detected in three distinct bands, with the predominant band occurring at pH 6.2.