Effects of Stocking Density on Growth of Tilapia nilotica Cultured in Cages in Ponds

Reported maximum carrying capacities of Tilapia nilotica reared in cages are Iow ranging from 10 to 70 kg/m³. This may be related to total numbers of caged fish reared in a body of water and not simply density per cage volume. An experiment was conducted to demonstrate such effects.
Sixteen cages in a 0.77 ha pond were stocked with T. nilotica at either 250, 500, 750, or 1,000 fish/cage for a total of 12,987 fish/ha. One cage in each of four 0.13 ha ponds was stocked with either 250 or 1,000 fish/cage for a total of 1,923 or 7,692 fish/hectare, respectively. Fish were fed a 32% protein diet at equal rates for 169 days. In the 0.77 ha pond, yield per cage was positively correlated with stocking density, while individual mean weights were negatively correlated with stocking density. However, among equal densities per cage between ponds, fish in the 0.13 ha ponds gained about 26% more than in the 0.77 ha pond. An interaction of the effects of density per cage volume and per pond area may have occurred.     

Agroforestry adoption and maintenance: self-efficacy, attitudes and socio-economic factors

Agroforestry is a key land use in the development of ecological corridors in tropical rainforests biomes. This research tested the social dimensions of agroforestry adoption and maintenance in the Atlantic rainforest of Southern Bahia, Brazil. A quasi-experiment research design compared a group of farmers who participated in an agroforestry development program with a group of similar farmers who were not participants in the program. The effects of the program on the participants’ self-efficacy, attitudes and intentions to adopt or maintain agroforestry were tested. The effects of socio-economic factors and attitudes were also compared to self-efficacy in terms of farmers’ intentions to adopt or maintain agroforestry. Results indicate that the program neither raised nor lowered the farmers’ attitudes, self-efficacy or intentions to adopt or maintain agroforestry. However, multiple regression and logistic model analyses indicate that perceived behavioral control, attitudes about conservation and available labor contributed most significantly to farmers’ intentions to adopt or maintain agroforestry. Overall, perceived behavioral control proved to have the most significant correlation with farmers’ intentions to adopt or maintain agroforestry. Therefore, agroforestry development programs could benefit from focusing on farmers’ perceived control of certain behaviors to enhance the persistence of agroforestry practices.     

Cover Image,Volume 76, Issue 11

The cover image is based on the Research Article First case of glyphosate resistance in weedy sunflower (Helianthus annuus) by Vijay Singh et al., https://doi.org/10.1002/ps.5917 .

     

PLASMA PROTHROMBIN CONCENTRATION IN DOGS GIVEN 3,3'-METHYLENEBIS(4- HYDROXYCOUMARIN) AND PURIFIED BEEF PROTHROMBIN

Purified beef prothrombin will antidote the hypoprothrombinemia induced in dogs by oral administration of 3,3'-methylenebis (4-hydroxyeoumarin). If the hypothesis is proven that this chemical compound acts only by preventing the production of prothrombin in the liver then the life of injected beef prothrombin is probably of the same duration as that of the dog's own plasma prothrombin; namely, 2 to 3 days.     

Effects of predation by largemouth bass in fish production ponds stocked with Tilapia nilotica

Triplicate ponds (0.07 ha) were stocked with either 0, 29, 86, or 143 largemouth bass fingerlings and 9500 Tilapia nilotica fingerlings (90% males) per hectare. Fish were fed a 32% protein ration for 6 months and then harvested. Average weight of largemouth bass declined as their stocking density increased. Average weight and total biomass of originally stocked tilapia increased with increasing predator stocking density. Total yields of tilapia were not different and averaged 4203, 4355, 4583 and 4230 kg/ha, of which recruits accounted for 28, 29, 26 and 8% for the above respective predator densities. Stocking 143 largemouth bass per hectare was an effective means of decreasing recruitment and increasing yields of larger sized male tilapia.