Search

High larval and frymortality has been amajor challenge to the commercial culture of the African bony-tongue (Heterotis niloticus). Research indicates inadequate feeding to be a possible cause of the high mortality rates of larvae/fry grown in captivity. An experiment was conducted to first describe the developmental stages of H. niloticus eggs and larvae until schooling, 6 days after hatching (DAH), at 26°C. The morphological development, survival, growth (weight gain and length), and swimming behavior of the larvae were monitored. A follow-up feeding trial was conducted with H. niloticus fry from 6 to 27 DAH involving four treatments: feeding with Artemia nauplii; a combined feed of 50% Artemia nauplii and 50% rotifers (w/w); feeding with rotifers; and no feeding. The activities of three digestive enzymes (trypsin, lipase, and amylase)were assessed in fry exposed to the live feed treatments. At hatching, the larvae had a large, vascularized yolk sac filled with yolk platelets, which occupied approximately one-third of the total body length of the abdominal cavity. Yolk platelet reabsorption started at 1 DAH and was complete at 6 DAH. Metamorphosis was completed at 6 DAH, and schooling behavior was observed. For the feeding trial, the fry that received Artemia nauplii underwent the fastest development until 27 DAH. Similarly, the survival rate was considerably higher in fry fed with Artemia nauplii than in those that received a combination of Artemia nauplii and rotifers or only rotifers. Overall, the survival rates for fry fed with Artemia nauplii and larvae co-fed were 72.7% ± 0.9% and 41.2% ± 3.3%, respectively. Fry did not survive until 27 DAH in the rotifer-fed and unfed treatment groups. Digestive enzyme activity differed significantly (p< 0.05) between treatments and sampling dates. All digestive enzymes were detectable at the onset of mouth opening (5 DAH) and fluctuated through the 7 and 9 DAH. Lower enzyme activity was observed when the fry were subjected to starvation or the rotifer treatment. Results indicate that Artemia nauplii is the best live feed organism for H. niloticus larviculture. [ABSTRACT FROM AUTHOR]

Donacidae is a commercially important family of heterodont bivalves and one of the few bivalve lineages that has successfully colonised brackish and fresh waters. However, to date, no phylogenetic hypothesis exists for this widely distributed group. Here we turn to molecular data from the nuclear and mitochondrial genomes and combine these with the extensive fossil record of donacids to propose an evolutionary hypothesis for the family. Our analyses strongly support the monophyly of Donacidae, including Galatea , Iphigenia and ' Plebidonax ' deltoides , but render Donax paraphyletic. The subgenus Latona is therefore elevated to genus to accommodate a clade of Indo-Pacific species, while retaining Donax for a clade of mostly Atlantic and American Pacific species, and a few Indo-Pacific species. This latter clade is sister group to Galatea + Iphigenia. The diversification of Donacidae seems to be tightly connected to the opening of the North and South Atlantic Oceans in the Cretaceous, and to the closing of the Tethys Ocean during the Oligocene. Taxonomic actions: Latona columbella (Lamarck, 1818) comb. nov. , L. deltoides (Lamarck, 1818) comb. nov. , L. dysoni (Reeve, 1854) comb. nov. , L. madagascariensis (W. Wood, 1828) comb. nov. , L. semisulcata semigranosa (Dunker, 1877) comb. nov. , L. spinosa (Gmelin, 1791) comb. nov. , L. sordida (Hanley, 1845) comb. nov. , L. siliqua (Römer, 1870) comb. nov. , L. trifasciata (Linnaeus, 1758) comb. nov. and L. victoris (Fischer-Piette, 1942) comb. nov. Donacidae has colonised brackish and fresh waters. Here we present a molecular phylogeny of Donacidae and use the fossil record to propose an evolutionary hypothesis for the family. Our analyses support the monophyly of Donacidae but render Donax paraphyletic. The subgenus Latona is used to accommodate a clade of Indo-Pacific species. The diversification of Donacidae seems to be tightly connected to the opening of the North and South Atlantic Oceans in the Cretaceous, and to the closing of the Tethys Ocean during the Oligocene. [ABSTRACT FROM AUTHOR]

This study assessed the physical characteristics, faecal, ammonia and phosphorus waste production rates of mixtures of groundnut, cottonseed, copra and soybean meals as a replacement for fishmeal in Nile tilapia diets. Six experimental diets were formulated such that the oilseed mixtures contributed 80% of total dietary protein. A fishmeal-based diet served as the control. The diets were randomly assigned in triplicates to the experimental tanks, containing 15 juvenile tilapia with a bulk weight of ~1 kg. Ammonia and phosphorus excretion rates of the diets were monitored at 3-hour intervals over 24 h. The pellet characteristics, faecal and nutrient waste production were assessed. The control diet recorded a mean bulk density of 376.00 ±5.19 g L-1 which was lower than the oilseed-based diets which ranged from 550.67 ± 3.06 g L-1 to 614.27 ± 2.08 g L-1. There was a positive correlation (p < 0. 0001; r = 0.93) between the sinking rates of pellets and their bulk densities. The oilseed-based diets recorded 4-45% higher faecal matter production compared to the control diet. Fish fed Diet 3 had the lowest Total Ammonia-nitrogen (TAN) excretion rate of 106.14±1.95 mg kg-1 while the control diet recorded the highest TAN excretion of 162.31 ±4.39 mg kg-1. Accumulated dissolved phosphorus was 64.52-74.09% lower in the oilseed-based diets compared to the control. [ABSTRACT FROM AUTHOR]

The study assessed the effect of oilseed meal mixtures on the biological value, faecal matter output, ammonia excretion rates and serum biochemistry of Nile tilapia over 63 days. The experimental diets (PPB 1, PPB 2 and PPB 3) were formulated using four selected oilseed meals that were mixed in different protein proportions to contribute 80% of total dietary crude protein. In each diet, either one or two of the oilseed meals were the dominant protein contributor. A commercial tilapia feed was used as the control diet (CTRL). Sex‐reversed Nile tilapia fingerlings (35 g) were stocked at 20 fish per tank in a recirculation system and fed at 3% body weight of their respective diets. At the end of the study, ADCs of dry matter, crude lipid and ash were significantly (p <.05) lower in all the plant‐based diets compared with the control diet. Fish fed the control diet had significantly higher weight gain and SGR compared with the plant‐based diets. Egesta output was 127% higher in the plant‐based diets compared with the control diet. All dietary treatments exhibited a similar trend in changes in ammonia nitrogen. Nevertheless, serum metabolites levels indicated no significant differences among treatments. Although the PPBs did not affect ADC of protein and serum profile, fish growth was reduced while faecal output increased. [ABSTRACT FROM AUTHOR]

Coastal erosion is a serious problem that affects the safety and livelihoods of many coastal dwellers along Ghana's coast. Despite the fact that coastal erosion is a natural phenomenon, erosion trends have been largely aggravated by human-induced factors. This study analyzed shoreline change rates for three neighbouring coastal communities in the Central region of Ghana; Elmina, Cape Coast and Moree. Two epochs were analyzed, 1974–2012 (medium-term) and 2005–2012 (short-term), using ArcGIS and Digital Shoreline Analysis System. Overall, the entire study area recorded average shoreline change rates of −1.24 myear−1and −0.85 myear−1in the medium-term and short-term period respectively. Less consolidated shoreline segments recorded higher erosion rates in both periods while cliffs and rocky segments experienced very little erosion or high stability. Because shorelines undergoing chronic erosion do not fully recover after short-term erosion events such as storms, facilities located close to such shorelines are threatened. Taking a proactive approach to coastal erosion management, such as coastal sand mining prevention, inter-sectoral land use management and adopting a construction setback approach may be prudent for the long-term management of the coast since this recognizes future shoreline changes and safeguards coastal landscape for other uses. [ABSTRACT FROM PUBLISHER]

The reproductive biology, sexual strategy and sex ratio of the freshwater donacidGalatea paradoxain the Volta River estuary, Ghana, was studied from March 2008 to February 2010. Histological observations of the gonads showed thatG. paradoxais gonochoristic with dominance by females (80%) and a high incidence of hermaphrodites (9.4%) for individuals ranged between 20 and 82 mm in shell length. There was a single spawning event between July and October. Gametogenesis started in December, progressing steadily to a peak in June–July when spawning began, until November when individuals were spent. The dominance of females coupled with the high incidence of hermaphroditism may be a reflection of populations subjected to increasing fishing pressure and over-exploitation. [ABSTRACT FROM AUTHOR]

Mining of sand and stone from the coasts provides an inexpensive source of materials for the construction industry while providing income to contractors. However, these activities come at a cost to the coastal environment and pose a threat to the tourism industry along the Ghanaian coast. This paper identified the various types of coastal sand and stone mining activities, the level at which they are undertaken and covers the trends in coastal erosion along the coast of Cape Coast, Ghana. ArcGIS (ESRI, Redlands, CA, USA) and Digital Shoreline Analysis System (DSAS; ESRI) tools were used to determine short-term (2005–2012) coastline changes using 2005 and 2012 coastlines data. This study estimates that tipper-truck-based beach sand mining activities alone account for the loss of about 285,376 m3/year of sand from the littoral zone in the Cape Coast area. It was also established that the average erosion rate for the Cape Coast area within the seven year period is 0.85 m/year with two areas recording high erosion rates of 4.35 m/year and 4.25 m/year. The study concludes that sand mining is the main cause of erosion along the coastline of Cape Coast. [ABSTRACT FROM PUBLISHER]

The trajectory of aquaculture growth in sub-Saharan Africa has necessitated closer attention to the use of environmental best management practices (BMPs). Two BMPs in particular, water reuse and floating feeds, are being promoted for adoption by pond fish farmers in sub-Saharan Africa. In this study, we investigated: (1) the effect of water source and feed type on water quality; (2) the effect of water source and feed type on tilapia growth; and (3) the quality of potential effluents from ponds using different water source and feed types. The study was conducted in Ghana using on-farm experiments involving monitoring of water quality and growth of Nile tilapia Oreochromis niloticus for 160 days. Although considered low-intensity production systems, nutrients and solids in the study ponds exceeded levels expected in intensive culture ponds by wide margins, whereas BOD5 was within the range for semi-intensive ponds. Floating feed was associated with higher water quality, especially dissolved oxygen, and higher growth, but water source did not significantly affect growth. Water reuse appears to be a viable BMP for sustainable aquaculture in the region, but the use of floating feed as BMP will depend on the economic profitability of floating feed use. [ABSTRACT FROM AUTHOR]

This study was conducted to assess the optimum clam size and substratum type for the culture of G alatea paradoxa. The experiment was conducted over a 90-day period at the Volta Estuary, Ghana. Three size classes of G . paradoxa categorized as small (27.6 ± 0.4 mm), medium (36.8 ± 0.4 mm) and large (50.0 ± 0.6 mm), were used to ascertain the effect of a sandy and muddy substratum on growth performance and survival. Growth increased from the small-sized clams to the large-sized clams at 2.54, 3.03 and 3.43 g, respectively, over the experimental period. Growth was higher ( P < 0.05) in the muddy substratum (3.58 g) compared with sandy (2.41 g). Similarly, the specific growth rate increased from 0.99% day−1 in the small-sized clams to 1.36% day−1 in the large-sized clams. Survival rates were significantly higher (99.4%) for the large-sized clams compared with the medium (78.8%) and the small-size clams (74.1%). There was significant interaction between the size class and the substratum type with a trend towards increasing survival rate from the small to the large size clams in both substrata. The survival rate was lower in the muddy substratum (71.4%) compared with the sandy substratum (96.7%). The yield was significantly higher in the muddy (2.01 kg m−2 90 day−1) compared with sandy substratum (1.87 kg m−2 90 day−1). The results of this study indicate that the culture of small-sized clams is best practiced on sandy substratum due to their elevated survival rates, whereas the muddy substratum appears most suitable for the culture of larger clams (>40 mm) because of their relatively higher survivorship and better growth performance. [ABSTRACT FROM AUTHOR]

This study was conducted to determine the effect of a sandy and muddy substrate on the growth and survival of three size-classes of Galatea paradoxa (Born 1778). The experiment was conducted over a 6-month period in a 1000 m2 pond at the research farm of the Faculty of Renewable Natural Resources. Three size classes (shell length) of G. paradoxa categorized as small (20–30 mm), medium (31–40 mm) and large (>40 mm) were used to ascertain the effect of a sandy and muddy substrate on growth performance. Growth in general was very slow, between 1.4 and 2.4 mm over the 6-month experimental period. The lengths measured at the end of the experiment were also significantly different. However, the mean length gained and the specific growth rate for the three size classes in the two substrates (sandy and muddy) were not significantly different ( P>0.05). The results of this study indicate that the pond environment is not suitable for the culture G. paradoxa as the species is adapted to life in a river with its filter-feeding activity dependent on the water current. The effect of the substrate type on growth was not significant. However, the substrate type did affect survival, with sandy substrates yielding in better survival than muddy ones. [ABSTRACT FROM AUTHOR]

The effects of processing by autoclaving (AC), soaking (SK), short-term fermentation (S-TF, 4 d) and long-term fermentation (L-TF, 14 d) on the nutritional composition, amino acid profile and some antinutrients were determined for cottonseed meal (CSM), groundnut meal (GNM) and groundnut husk (GH) in this study. After processing, crude protein content improved by 11% after L-TF, and crude lipid content 25% after SK for CSM; crude protein content improved by 27% after S-TF and L-TF, and crude lipid content 13% after SK for GNM. Soaking and fermentation were shown to significantly increase essential amino acid contents by 44% (SK, methionine) in CSM and 46% in GNM (L-TF, histidine). Phosphorus content was reduced by 59% in CSM and 57% in GNM by L-TF. All processing techniques, with the exception of AC, reduced phytic acid and gossypol contents in CSM and GNM. It was concluded that SK and fermentation were simple, cost-effective, and efficient ways to improve the nutritional value of the selected oilseed by-products.