Glyphosate‐resistant Italian ryegrass (Lolium multiflorum) on rice paddy levees in Japan

The rapid range expansion of naturalized Italian ryegrass (Lolium multiflorum Lam.) in farmland is a serious problem in Fukuroi city in Shizuoka Prefecture, Japan. Glyphosate has been used to control Italian ryegrass in the levees of rice paddy fields and wheat fields for ～20 years, but this weed in Fukuroi city is poorly controlled by glyphosate. In order to elucidate the level of resistance to glyphosate in Italian ryegrass populations, seed bioassays and a foliar application experiment, using seeds collected from 16 wild populations in and around Fukuroi city and from three susceptible cultivars, were conducted. For the susceptible cultivars and one population from a site where glyphosate had not been applied for >10 years, the shoot length in the seed bioassays was greatly suppressed at a glyphosate concentration of 10 mg ai L^?1 and no seedling survived after the foliar application of glyphosate at a rate of 2.3 kg ai ha^?1. Nine wild populations from levees in the southern part of Fukuroi city showed vigorous shoot growth at a glyphosate concentration of 10 mg ai L^?1 and had at least a 78% survival rate after the application of glyphosate at 2.3 kg ai ha^?1. Four wild populations from levees in the northern part of Fukuroi city showed a slight suppression of the shoot growth as a result of the glyphosate treatment and their survival rates ranged from 20 to 64%. The results suggested that resistance to glyphosate has evolved in the wild populations of Italian ryegrass that are growing on the levees. This is the first report of a glyphosate‐resistant weed in Japan.     

Genotyping‐by‐sequencing for construction of a new genetic linkage map and QTL analysis of growth‐related traits in Pacific bluefin tuna

Pacific bluefin tuna (Thunnus orientalis) has high market value, but its wild populations have decreased in recent years. The broodstock of Pacific bluefin tuna that were hatched artificially and reared under aquaculture conditions is beginning to be used for production. The creation of broodstock with commercially valuable traits, such as rapid growth, is therefore of great interest. Genetic linkage map‐based identification of markers associated with quantitative trait loci (QTLs) facilitates marker‐assisted selection (MAS) breeding and allows efficient genetic improvement of broodstock. Single nucleotide polymorphism (SNP)‐based genetic linkage map construction using the genotyping‐by‐sequencing method can expand the number of mapped markers and help identify growth‐related QTLs. In this study, we constructed sex‐specific maps for 24 linkage groups consisting of 677 SNP and 651 microsatellite markers. The total lengths of 93 progenies in the mapping population followed normal distribution, with an average length of 9.4 mm. We performed composite interval mapping in the mapping population. QTL analysis revealed one significant QTL in LG10 on the female linkage map. The genetic linkage map—the second such map generated for Pacific bluefin tuna—and the growth‐related QTLs detected in this study will be useful for tuna aquaculture MAS programs.     

Positive phototaxis as the cause of jaw malformations in larval greater amberjack,Seriola dumerili (Risso, 1810): Mitigation by rearing in tanks with low‐brightness walls

Jaw malformations are a serious problem in fingerlings of the greater amberjack, Seriola dumerili. To establish a countermeasure against these malformations, we conducted a larval behavioural test to identify their root cause, and we investigated the ability of low‐brightness rearing tank walls to control their occurrence. Larval distribution was examined in a horizontally illuminated rectangular transparent aquarium (20 cm × 100 cm × 25 cm), and their distribution was biased towards the light source after this lighting was provided from 3 to 13 days post hatching (dph), indicating positive phototaxis; this response disappeared on 22 dph (there are no data between 13 and 22 dph). Larvae were observed to swim phototactically towards the light source and repeatedly collided with the tank wall (walling behaviour). To investigate the ability of wall brightness to control the incidence of jaw malformations, we compared their incidence in a rearing trial with different Munsell colour values for the tank walls: 2.11 (black), 5.85 (grey) and 9.52 (white). The incidence rate of jaw malformations at 25 dph was significantly lower in the tanks with lower‐brightness walls, that is, 5.8%, 22.5% and 26.8% for black, grey and white respectively. Larval walling behaviour was most intense for white, followed in order by grey and black. These results indicate that positive phototaxis elicits larval walling behaviour, causing jaw malformations, and that low‐brightness tank walls control this process.     

Effect of dietary taurine enhancement on growth and development in red sea bream Pagrus major larvae

This study investigated the effect of feedings taurine‐enriched rotifers on the growth and development of larval red sea bream (RSB). Rotifers incubated in taurine‐enriched water at a taurine concentration of 800 mg L^?1 (T‐800) and 0 mg L^?1 (T‐0) were fed to larvae from 3 to 20 days after hatching (DAH). Notochord length, body weight and specific growth rate of T‐800 group were significantly greater than those of T‐0 at 14, 17, 9–11 and 18–20 DAH. Taurine content of larvae in the T‐800 group increased rapidly from 11 DAH and thereafter remained significantly higher than T‐0. Flexion larvae firstly appeared in both groups at 8 DAH, however, at 20 DAH post‐flexion larvae were significantly more abundant in T‐800 than T‐0. While nucleic acid and protein contents (μg mg^?1 wet fish) showed remarkable changes, ontogenetic growth in RSB larvae stage was observed to switch from hyperplastic growth to hypertrophic growth with the start of the flexion stage. Although a similar change in nucleic acid contents was observed between the two groups, the protein content (μg fish^?1) and protein/DNA ratio of T‐800 remained higher than that of T‐0 during the hypertrophic growth period. These results suggest that dietary taurine accelerates the growth and development in RSB larvae especially during hypertrophic growth (flexion stage) after the early hyperplastic growth.     

Single spaghetti tagging as a high-retention marking method for Japanese common sea cucumber <Emphasis Type="Italic">Apostichopus japonicus</Emphasis>

Populations of sea cucumbers, including the Japanese common sea cucumber Apostichopus japonicus, have been seriously depleted worldwide due to overfishing. Mark–recapture study is an efficient means of collecting ecological data. However, the use of such a method in sea cucumbers is difficult because they lack hard tissues in the body wall. Here we tested the viability of various tagging methods on A. japonicus. First, we applied conventional tags using four different methods [single spaghetti (T-bar) tagging, double spaghetti tagging, ribbon tagging, and Atkins tagging] to ten individuals per method in aquaria for 14 days. Of the methods used, single spaghetti tagging had the highest retention rate. Then we examined the retention rate of single spaghetti tags on ten individual sea cucumbers for up to approximately 6 months in rearing conditions. The single spaghetti tagging method showed a retention rate of 100% over at least 7 days, and 50% of the tags remained embedded after 56 days. The longest duration of tag retention was 174 days, at which time the experiment was terminated. These results indicate that single spaghetti tagging is reliable for both short- and longer-term studies, making it a useful tool for ecological and conservation studies in sea cucumbers.