Biotic and abiotic controls on body size during critical life history stages of a pelagic fish,Pacific herring (Clupea pallasii)

Variation in growth and body size during critical life history stages can have important implications for life history schedules and survivorship. For Pacific herring (Clupea pallasii), there is still debate as to whether juvenile body size is governed by density‐dependent or ‐independent processes and few have evaluated whether the relative importance of either process shifts over the course of early ontogeny. We used a unique data set consisting of seasonal measurements of abundance, body size, and spatial distribution within a semi‐enclosed basin of Puget Sound (Washington State, U.S.A.) to measure the relative importance of temperature and cohort abundance on body size at distinct time periods, and evaluated whether density‐dependent habitat shifts might be responsible for density‐dependent growth. Over the 9 years of sampling (2001–2010) midsummer body size was positively related to temperatures experienced during the egg/yolk sac and larval stages and unrelated to cohort abundance. However, fall body size was negatively correlated with abundance and uncorrelated with both midsummer body size and temperature, indicating a shift from density‐independent to density‐dependent control over the course of the growing season. Thus, density‐dependent effects may supplant density‐independent effects exhibited early in herring life history. Our data on spatial distributions of herring and their zooplankton prey indicate that density‐dependent reductions in growth may be explained by density‐dependent habitat shifts that lead to reduce overlap of herring with zooplankton. Evidence of density‐dependent growth in marine fish populations is often attributed to exploitative competition, but our results suggest that these patterns may partly be mediated by density‐dependent distribution expansions in to prey‐poor habitat.     

全膜双垄沟播玉米密度对产量及植株性状的影响研究

通过在全膜双垄沟播技术模式下6个耐密型玉米杂交种不同密度（4．5、5．25、6．0、6．75、7．5万株· hm－2）的试验,研究了玉米产量及其性状与种植密度的关系。在本文研究密度范围内,玉米的产量随着密度的增加而增高;当密度达到一定程度之后,随着密度的增加,产量反而下降,二者呈二次曲线模式变化 Y＝－6417．314＋5501．842 X－396．330 X2。结果表明,6个耐密型玉米杂交种在双垄全膜沟播技术模式下最佳密度为6．941万株· hm－2。此密度下各植株性状指标为：穗粒数为499．9粒、百粒重为38．63 g、出籽率为83．71％、穗长为17．5 cm、株高194 cm、茎粗2．14 cm、秃顶长1 cm。株高与密度之间为正相关,函数曲线是幂模型 Y＝140．607 X0．16602,穗粒数、穗粗、茎粗、出籽率4个性状与密度之间为负相关,函数模型均为性状指标随密度的增加而减少的三次曲线。秃顶长、穗长、百粒重与密度的关系呈二次曲线模式变化。密度与秃顶长之间为正相关,与穗长、百粒重之间为负相关。秃顶长随着密度的增大而增加;穗长、百粒重随密度的增加而呈单边下降的变化趋势。穗位高与密度的相关不显著。     

温度和密度对日本医蛭繁殖的影响

在实验室网箱中,研究温度(24±1)℃和(20±1℃)与密度(200尾/箱和100尾/箱)对平均体质量1g左右的日本医蛭Hirudo nipponia亲蛭交配率、减重率、产茧数量和体质量的影响,比较卵茧质量(0.05g、0.05~0.1g和0.1g)对孵出仔蛭数量的影响。结果表明:温度(24±1)℃、密度100尾/箱时亲蛭交配率(86±0.06)%和平均产茧量(0.87±0.14)枚/尾最高;亲蛭产茧后平均体质量下降(32.1±0.059)%;繁殖期间共收集卵茧870枚,孵化率87.47%;平均卵茧质量为(0.11±0.009)g(变化范围0.03g~0.25g);密度和温度对产茧量的影响极显著(P0.01),对卵茧平均质量和长短径的影响不显著(P0.05);(24±1)℃组亲蛭的产茧时间比(20±1)℃组缩短10~15d,单日卵茧最高收集量为43枚,(20±1)℃时单日最高收集量24枚;卵茧共孵出仔蛭5 648尾,随着卵茧质量增加产出的仔蛭数量和质量也增加。     

Effects of stocking density on production and economics of Nile tilapia (Oreochromis niloticus) and freshwater prawn (Macrobrachium rosenbergii) polyculture in periphyton-based systems

The present research investigated the effect of stocking density on pond (75 m², depth 1.2 m) production of Nile tilapia (Oreochromis niloticus) and freshwater prawn (Macrobrachium rosenbergii) stocked at a fixed 3:1 tilapia:prawn ratio. Three stocking densities were tried in triplicate: 20 000 ha⁻¹ (treatment TP‐20), 30 000 ha⁻¹ (TP‐30) and 40 000 ha⁻¹ (TP‐40). The ponds were provided with bamboo as substrate for periphyton development. Bamboo poles (mean diameter 5.5 cm and 5.0 poles m⁻²) were posted vertically into pond bottoms, resulting in 60% additional substrate area in each pond. On average, 43 genera of algae and 17 genera of zooplankton were identified from pond water, whereas 42 genera of algae and six genera of microfauna were attached to bamboo substrates. No differences were observed between treatments in the ash‐free dry matter (AFDM), chlorophyll a and phaeophytin a content of periphyton (P>0.05). Survival of tilapia and prawn and individual weight gain of tilapia were lower (P<0.05) in treatment TP‐40. The net yields were higher (P<0.05) in treatments TP‐30 (2209 and 163 kg ha⁻¹ 105 day⁻¹ of tilapia and prawn respectively) and TP‐40 (2162 and 141 kg ha⁻¹ of tilapia and prawn respectively) than in treatment TP‐20 (1505 and 136 kg ha⁻¹ of tilapia and prawn respectively). The net tilapia yields were quadratic correlated (R²=0.92) with fish stocking density. The cost–benefit analysis shows that the net profit margin was highest in treatment TP‐30 (69%), followed by TP‐20 (50%) and TP‐40 (44%).     

Nursery rearing of kalbasu, Labeo calbasu (Hamilton), at different stocking densities in outdoor concrete tanks

The growth and survival of kalbasu, Labeo calbasu, was evaluated at stocking densities of 5, 10 and 15 million spawn ha⁻¹ in nursery rearing in concrete tanks of 50 m², each for a period of 25 days. Survival of fry was density dependent and significantly higher (54.5%) at 5 million ha⁻¹ than those at 10 million ha⁻¹ (50.1%) and 15 million ha⁻¹ (46.9%). Similarly, growth and specific growth rate were inversely related to the stocking density and varied significantly among the three densities.     

饵料种类和密度对毛蚶浮游幼虫生长的影响

通过投喂不同种类和不同浓度藻类对毛蚶浮游幼虫的生长进行了研究。结果表明在三种不同的单细胞藻类中湛江球等鞭金藻的效果最好,微绿球藻次之,而小球藻最差。在不同饵料浓度下,表明在初期投喂5×107L-1(cells/L)比较适宜,而后期以10×107L-1比较合适。     

Changes in the density and growth of brown trout (Salmo trutta) after intensive removal of sympatric Arctic charr (Salvelinus alpinus) in the sub‐Arctic lake Møkkelandsvatn,Norway

This study tests the basic hypothesis that the removal of charr, Salvelinus alpinus (L.), would cause an increase in both the growth and density of a sympatric trout population, Salmo trutta L. The charr population was characterised by slow‐growing individuals, with a high proportion of mature fish, that is typical for so‐called overpopulated populations. A total of 31,000 charr was removed from the lake in the period 1990–1992, and the density of younger trout (1+, 2+), but not older trout (3+, 4+), increased. The growth of older trout (3+, 4+) increased, but the evidence for similar growth increases of younger trout (1+, 2+) was limited. From 1989 to 1990, the proportion of trout increased from 30 to only 40% of the total catch, but from 1991 to 1994, it was significantly higher (60–80%) than that of charr. Total trout biomass increased to a maximum in 1992 and then decreased so that the biomass of 1994 was nearly similar to that of 1989, that is before the start of the charr removal. Back‐calculated lengths of trout from otoliths showed that 2+ and 3+ trout caught in the pelagic were growing consistently faster over previous years than those caught in the littoral, while this was not the case for the 4+ fish. Therefore, the hypothesis was partially supported; the growth rate of trout increased (age groups 1+ to 4+), while the density of juvenile trout (1+, 2+), but not the older trout (3+, 4+), increased after the removal of charr.     

Effects of stocking density on survival,growth and biochemical composition of cultured mussels (Mytilus galloprovincialis,Lamarck 1819) from an offshore submerged longline system

This study examined an offshore submerged mussel longline system, in the Black Sea, from May 2009 to May 2010. The system was allowed 1 year for spat collection. After a 1‐year spat collection period, some spat collectors were left untouched (NS), and some spat collectors were grazed and socked (S) for a grow‐out study in May 2009. The effects of stocking density on the growth and survival of the S and NS mussels were examined. The biochemical composition of the mussels was also determined. Environmental factors including temperature, salinity, chlorophyll a, total suspended matter, inorganic matter and organic matter were monitored monthly during the experimental period. In May 2010, the mean length and live weight of the S and NS mussels were 60.46 ± 0.60 mm and 53.34 ± 0.37 mm, respectively, and 20.50 ± 0.50 g and 13.11 ± 0.26 g respectively. Mean moisture and ash were 82.35 ± 0.47% and 6.67 ± 0.44% respectively. Mean carbohydrate, protein and lipid were 27.74 ± 2.40%, 57.68 ± 2.15% and 7.91 ± 0.68% respectively. These results indicate that a submerged offshore mussel culture system in the Black Sea can be commercially convenient. In addition, stock management via thinning out of the spat can considerably increase the marketable size of mussels, reduce harvest time and produce better growth.     

The effect of stocking density and repeated handling on the growth of juvenile mulloway, Argyrosomus japonicus (Temminck & Schlegel 1843)

The effect of stocking density on the growth of mulloway, Argyrosomus japonicus, was tested with 17 g fish stocked at 4.08, 8.16, or 16.32 kg m⁻³ in 50 l aquaria. Weight checks were carried out every 2 weeks to track performance. Each density treatment was also compared to a nonhandled control group to establish if handling during weight checks influenced the growth of mulloway. Mulloway performed poorly at the lowest density and, under the current experiment conditions, growth did not appear to be negatively affected by regular handling.