Structural variability and distribution of cells in a posterior gill of<i>Carcinus maenas</i>(Decapoda: Brachyura)

Gill number 8 of intermoult maleCarcinus maenas(L.) (Decapoda: Brachyura) was used to study the morphological variation and distribution of the major gill cells. Three gill regions (proximal, mid and distal) were sectioned and examined by light and transmission electron microscopy. The ultrastructure of the three epithelial cell types (striated, chief and pillar) was similar to previously published descriptions, but some variations in cell form and distribution were observed. In all gill regions, striated and chief cells were larger towards the lamellar raphe than near the marginal canal. In the proximal gill region, the epithelium consisted almost exclusively of striated cells, implying an osmotic/ionic role for this region. In the mid gill region, the epithelium comprised a mixture of chief and striated cells. In the distal region, chief cells predominated, implying a respiratory role for this region. Pillar cells exhibited no clear distributional pattern within the gill and, although their shape varied with position, their involvement in ionic regulation, osmoregulation, respiration, structural support or the flow of haemolymph through the gill is not clearly defined. Nephrocytes, thought to be involved in gill defence mechanisms, occurred in the haemolymph space or attached to the intralamellar septum and showed no structural variability. Glycocytes were always associated with the intralamellar septum, implying that there are specific gill regions for glycogen storage. Haemocytes showed some structural variation but there was no obvious correlation with gill region; small-granule haemocytes were the most common haemocyte type in the gill.</jats:p

A universal equation to predict methane production of forage-fed cattle in Australia

The methods for estimating methane emissions from cattle as used in the Australian national inventory are based on older data that have now been superseded by a large amount of more recent data. Recent data suggested that the current inventory emissions estimates can be improved. To address this issue, a total of 1034 individual animal records of daily methane production (MP) was used to reassess the relationship between MP and each of dry matter intake (DMI) and gross energy intake (GEI). Data were restricted to trials conducted in the past 10 years using open-circuit respiration chambers, with cattle fed forage-based diets (forage >70%). Results from diets considered to inhibit methanogenesis were omitted from the dataset. Records were obtained from dairy cattle fed temperate forages (220 records), beef cattle fed temperate forages (680 records) and beef cattle fed tropical forages (133 records). Relationships were very similar for all three production categories and single relationships for MP on a DMI or GEI basis were proposed for national inventory purposes. These relationships were MP (g/day) = 20.7 (±0.28) × DMI (kg/day) (R2 = 0.92, P < 0.001) and MP (MJ/day) = 0.063 (±0.008) × GEI (MJ/day) (R2 = 0.93, P < 0.001). If the revised MP (g/day) approach is used to calculate Australia’s national inventory, it will reduce estimates of emissions of forage-fed cattle by 24%. Assuming a global warming potential of 25 for methane, this represents a 12.6 Mt CO2-e reduction in calculated annual emissions from Australian cattle