Partial and complete replacement of fish meal with gambusia meal in diets for red tilapia 'Oreochromis niloticus × O. mossambicus'

A 12‐week experiment was conducted to evaluate the suitability of gambusia (Gambusia affinis) fish meal (GFM) as a partial and complete substitute for the protein supplied by herring fish meal (HFM) in diets for red tilapia fingerlings (mean weight 0.42 g). Seven isonitrogenous (35% crude protein), isolipidic (9% fat) and isoenergetic (15.9 kJ DE‐g^?1 diets were formulated in which GFM replaced 0.0, 10, 25, 50, 75, 90 and 100% of the protein supplied by HFM. In general, GFM exhibited good potential as a substitute for HFM in red tilapia diets with no adverse effects on growth, feed efficiency, body composition, blood parameters or apparent digestibility of dry matter, protein and gross energy compared with the HFM‐based control diet. Growth performance (in terms of final weight, weight gain, per cent increase in weight and growth rate) of fish fed diets containing GFM at 25 or 50% level of replacement for HFM‐protein (diets 3 and 4) was statistically higher than for fish fed diets containing GFM at replacement levels >50%. Diet 4 had the best economic efficiency of fish weight gain. Partial or complete substitution of GFM for HFM did not affect feed utilization efficiency (in terms of FCR, FER, PER and APU) or digestibility coefficients of dry matter, protein and gross energy compared with those of the HFM‐based diet. Apparent protein digestibility varied little between diets, ranging from 84.2 to 87.3% with no significant differences. Survival of fish fed all the experimental diets (except for fish fed GFM at 90 or 100% level of replacement for HFM‐protein) was comparable with that of fish fed the control diet and ranged from 91.7 to 98.3%.     

Management of interactions between endangered species using habitat restoration

Commonly used conservation strategies may be insufficient when deleterious interactions between co-habiting endemic species occur. The decline in the population size of the endangered Leon Springs pupfish, Cyprinodon bovinus, in Diamond Y Spring, Texas has been partially attributed to egg-predation by the endangered Pecos gambusia, Gambusia nobilis. This interaction is related to changes in habitat availability; therefore, we aim to manage the conflict via restoration of the breeding habitat. We hypothesized that altering the habitat to expand shallow breeding areas would result in a decrease in the number of gambusia preying on the eggs of spawning pupfish pairs and an increase in the number of males defending territories. In 2 years following the habitat modification, we observed resurgence in the pupfish breeding population and a decrease in egg-predation pressure around spawning pupfish pairs. Additionally, after altering the habitat, gambusia were more dispersed throughout the habitat, as the low numbers of gambusia in a territory were stable regardless of spawning or aggressive behaviors by pupfish. To our knowledge, this is the first empirical example of effective management of deleterious interactions between two endangered species by means of habitat restoration.     

Postflood movements and population connectivity in gambusia (Gambusia holbrooki)

Abstract –  A population of the exotic pest fish Gambusia holbrooki inhabiting a drainage channel was sampled regularly to record responses to flooding and subsequent population reestablishment. The flood reduced numbers in the channel to near-zero levels. After remaining very low for 2 months, densities increased steadily through juvenile recruitment and the concentration of fish in drying pools. Tagging revealed that in general, movements between pools separated by only a few metres were relatively limited. There was evidence for habitat segregation and population subdivision, as fish from different pools varied markedly in terms of mean population density, movement behaviour, sex and size composition and juvenile recruitment. The most favoured pool was relatively deep, well lit and had the greatest habitat diversity. Gambusia control measures are likely to be most effective if timed to coincide with floods (which reduce local population densities) and/or droughts (which concentrate fish and allow targeting of source populations).     

利用食蚊鱼目标基因转录水平评价四会市 邓村河雌/雄激素物质污染现状

利用西部食蚊鱼(Gambusia affinis)的雌/雄激素受体(ER α/ARα)基因和卵黄蛋白原(VTGα)基因的转录水平为生物学指标,对广东省四会市邓村河的雌/雄激素物质污染现状进行评价.结果显示,与未受造纸废水污染的对照点REF相比,受造纸废水污染位点A、B、C中雌性食蚊鱼臀鳍中的雄激素受体ARα mRNA转录水平均比对照点显著升高(P＜0.05),雄性食蚊鱼臀鳍的雌激素受体ERα转录水平不明显(P＞0.05).造纸废水暴露位点A、B、C中雄性食蚊鱼肝脏中的VTG受体VTGα mRNA转录水平均比对照点显著升高(P＜0.05).结果表明,生活在受造纸废水污染的邓村河中的食蚊鱼受雌/雄激素物质干扰明显,且受雄激素物质污染更严重.鱼类肝脏VTGα基因和臀鳍ARα基因转录水平可适合作为监测水体环境雌/雄激素物质的生物标志物.