Microbial decomposition process of organic matter in sinking particles,resuspendable particles,and bottom sediments at a coastal fish farming area

The possible impacts of resuspension of low-density bottom sediments on the microbial decomposition process of organic matter were investigated at a coastal fish farming area. Hydrolysis and mineralization rates were much higher in sinking particles, resuspendable particles, and bottom sediments than in seawater. The cell-specific mineralization rate of free-living bacteria in seawater was several times higher than that of particle-associated bacteria at the other three sites. Conversely, no significant difference was observed in the cell-specific ecto-enzymatic hydrolysis rate. These results indicated different strategies in the utilization of organic matter: free-living bacteria actively respire low-molecular-weight compounds produced from the high-molecular-weight compounds resulting from extracellular enzyme activity of particle-associated bacteria. Both hydrolysis and mineralization were higher in sinking particles than in the other three sites. Hydrolysis rates were higher in resuspendable particles than in bottom sediments. Furthermore, leucine aminopeptidase and mineralization rates tended to be highest during winter in all four sites within the water column. These results suggest that the microbial decomposition of organic matter is stimulated by the resuspension of bottom sediments, especially during winter, when vertical mixing is relatively strong.     

Heavy metal concentrations and sediment quality of a cage farm on Lake Volta,Ghana

This study involved the determination of sediment quality and heavy metals in the water column and bottom sediment of a selected cage fish farm in Lake Volta, to assess the potential impact of metals and organic matter pollution on the lake due to cage fish farming. Sediment analysis indicated that the texture of all sampling sites was sandy clay loam with sand dominating with a range of 31.5%–81.2%. The organic matter (TOM) ranged from 4.42%–8.89%, while organic carbon (TOC) was from 2.57%–5.22%. Total nitrogen (TN) fluctuated between 0.22% and 0.45%; total phosphate ranged between 0.22% and 5.30%. The TOC, TOM and TN content in the farm sediment were significantly lower than those of the reference sites (ANOVA, p < .05). Lead, copper, cadmium and selenium were not detected in the water. The results revealed that heavy metal concentrations in the water column and sediments were low and within tolerable levels, indicating no influence of metals from fish feed was observed on the lake water quality. However, the farm seemed to have moderate impact on sediment quality from organic matter. Water and sediment quality monitoring should be embarked upon periodically to ensure sustainable cage culture in the Lake Volta.     

A note on the behaviour of adult Atlantic halibut, Hippoglossus hippoglossus (L.), in cages

Abstract. Observations of adult Atlantic halibut, Hippoglossus hippoglossus (L.), behaviour in cages were made with underwater camera and video recording equipment. Significantly more fish ( P < 0·01) were found on the cage bottom than in the water column, fish tending to congregate around the outside rather than in the centre of the cage. During rough weather, the cage bottom was observed to heave violently and proportionately fewer fish remained on the bottom, those which did adopting an arched body posture with heads and tails not in contact with the cage bottom. Around 25% of the caged fish were active at any time, most of the active fish remaining close to the cage surface or bottom, with little use being made of the remaining cage volume. Fish were observed to swim in a circular pattern close to the cage walls (mean velocity 0·53 m/s), maintaining such behaviour for periods of up to 5min with little change in swimming speed. Whilst all food types were ingested, items delivered directly lo the cage bottom were taken only if detected within the first minute or so. The implications for rearing Atlantic halibut in conventional cages are discussed.     

Effects of lining and drying on the chemical composition of sediments and influence of organic carbon on carp growth in aquaculture ponds

Chemical characteristics and P‐fractionation of sediments from the Deroua fish culture farm (Beni Mellal, Morocco) were analysed in 1998 and 1999. The high concentrations of organic N and organic C in the sediments reflect the high productivity of phytoplankton in the lined ponds. Despite the fact that these ponds were not frequently fertilized, inorganic P was more important in the sediments. The P released from CaCO₃≈P was the principal source of P for phytoplankton. The mineralization rate of organic C during the drying period was about 87 µg g^?1 day^?1 in the sediments. The mineralization rate of organic N seems to be less, compared with organic C. The experimental results indicate that the C:N ratio and texture of sediments could explain the immobilization of organic N. All forms of P remained almost unchanged after the drying period except for Fe(OOH)≈P. The ferric (oxy) hydroxides protect NaOH_ext‐P from the bacterial lyses and stabilize therefore their concentration. The inorganic P represented about 88% of Total P in the sediments and may influence the mineralization rate of organic P. The growth of silver carp were reduced in presence of high concentrations of organic C in sediments (> 30 mg/g). Compounds toxic to fish such as Fe²⁺, Mn²⁺, H₂S and CH₄ were then released in the water column.     

网箱与微流水养殖的齐口裂腹鱼肌肉营养成分的比较与分析

本研究比较和分析网箱与微流水两种养殖模式下体质量(76.5±17.8)g和(67.2±8.1)g的齐口裂腹鱼Schizothorax prenanti肌肉常规营养成分。结果显示:两组齐口裂腹鱼肌肉中一般营养成分含量不存在显著性差异,均含有18种氨基酸;除色氨酸(Trp)和组氨酸(His)外,网箱组齐口裂腹鱼肌肉中其余氨基酸、氨基酸总量、必需氨基酸总量和鲜味氨基酸总量均显著低于微流水组。氨基酸评分(AAS)和化学评分(CS)结果显示:两组齐口裂腹鱼肌肉中必需氨基酸构成合理,色氨酸均为第一限制性氨基酸,赖氨酸在必需氨基酸中评分最高。两组齐口裂腹鱼肌肉中均含有21种脂肪酸,网箱组饱和脂肪酸(SFA)总量和单不饱和脂肪酸(MUFA)含量显著低于微流水组,而多不饱和脂肪酸(PUFA)含量显著高于微流水组,且n-3/n-6比值要高于网箱组。综上所述,微流水养殖的齐口裂腹鱼营养价值更高。     

大亚湾鱼类深水网箱养殖对环境的影响

2016年5月(养殖开始前)和2016年8月(养殖投饵高峰期)对大亚湾大碓鱼类深水网箱区、外围区(网箱外0.1 km)和非养殖区(网箱外10~15 km)的海水和沉积环境进行了调查,采用有机污染指数(A)法、营养状态质量指数(NQI)法对水环境进行评价,用潜在生态危害指数(RI)法对表层沉积物重金属潜在生态危害进行评价。结果显示,与传统网箱养殖化学需氧量(COD)由网箱区中心向四周递减的趋势不同,深水网箱养殖CODMn浓度在3个区域间无显著性差异。深水网箱养殖海域水质较好(A1),水质处于贫营养水平(NQI2)。深水网箱养殖海域表层沉积物重金属铅(Pb)和锌(Zn)含量均符合第一类海洋沉积物质量标准,但铜(Cu)和镉(Cd)含量轻微超标。沉积环境处于轻微生态危害状态(Eir30,RI100),与中国同类型海区相比,污染危害程度相对并不严重。深水网箱养鱼对周围海域环境的影响较小。     

网箱养殖对东湖沉积物有机质含量以及磷的酶促水解与吸附行为的影响

东湖养殖非鱼（Oreochromis niloticus）的网箱下沉积物中有机质和可酶解磷（PHP）含量以及碱性磷酸酶活性（APA）均显示增高,间隙水中的PHP较低,而APA与正磷酸盐的浓度均高,这种现象在垂直与水平两个尺度上均有体现,故由有机物的富集到正磷酸盐的剧增可能受控于酶学机制。Langmuir单分子等温度吸附模型的分析结果表明网箱下表层沉积物的最大吸附量明显较高,面吸附强度明显降低,此亦为正磷酸盐相应剧增的另一重要原因。不同深度间隙水中APA的动力学行为表现出明显的季节性。     

Effect of organic nitrogen and carbon mineralization on sediment organic matter accumulation in fish ponds

In aquaculture, ponds with high loads of organic inputs, organic matter accumulates at the bottom over time. Uneaten feed, senescent phytoplankton and faeces are the principal sources of accumulated material, but quantifications are scarce. The sedimented organic matter develops into a flocculent layer in which different processes transform the material into inorganic forms. A better understanding of factors influencing organic matter accumulation/decomposition in the sediment is needed to better understand and manage the dynamics of nitrogen in fish ponds. In this study, the rate of mineralization of organic nitrogen and the nitrogen flux between the sediment and the water column were measured. Organic matter accumulation in fish ponds was quantified, and the data were used to construct, calibrate and validate a dynamic simulation model of organic matter deposition/decomposition in fish ponds. The accumulating material consisted of dead phytoplankton, fish faeces and uneaten feed. Through model calibration, the proportion of these materials in the total accumulated organic matter was determined. In the model, gross photosynthetic rate was estimated from an empirical relationship with feed input. After calibration, the model was validated using independent data. The model simulated well the concentrations of organic carbon and nitrogen in the sediments but it may be developed further, especially by considering the effects of resuspension.     

The fate of organic matter derived from small-scale fish cage aquaculture in coastal waters of Sulawesi and Sumatra, Indonesia

To determine the fate of organic matter derived from fish cage aquaculture, carbon and nutrient cycling processes in waters and sediments, and water circulation, were examined at two fish cage farms of different size and utilizing different food types, on Sulawesi and Sumatra islands, Indonesia. Mass balance models of C, N and P were constructed to assess the pathways of waste utilization and dispersal. At the smaller farm in Sulawesi (64.5 m² cage area; 3 t annual net production) using pelleted food, there was proportionally less waste (≈ 40% of total C input) than at the larger Sumatran farm (2432 m² cage area; 9 t annual net production) using trash fish (≈ 70% of total C input) as food. At the small farm, the mass balance and hydrographic models indicated a maximum dispersal area of 1180 m², equivalent to 18 times the farm area. Within this area, 30% of total organic matter input (farm waste + fixed phytoplankton carbon) was buried in sediments with 30% mineralized in the water-column and 40% mineralized in the seabed. At the larger Sumatran farm, the models indicated a maximum dispersal area of 29  220 m², roughly 12 times the farm area. Within this area, 30% of total organic matter input (farm waste + natural pelagic input) was buried in sediments with 50% mineralized in the water-column and 20% mineralized on the seabed. There was some evidence of benthic enrichment at both farms, mostly as enhanced dissolved nutrient release, but sulfate reduction accounted for < 25% of total C flux, and denitrification/ammonium oxidation accounted for only 4–17% of N lost from sediments. There was no clear evidence of impact with distance from the cages at either farm. Phytoplankton gross primary production accounted for 60–77% of the total organic input to the receiving environment, suggesting that the relative importance of fish cage wastes must be assessed against natural inputs of organic matter.     

Bioturbation of sediments by benthic macroinvertebrates and fish and its implication for pond ecosystems: a review

Bioturbation of bottom sediments at the sediment–water interface is currently gaining more attention in studies dealing with the functioning of aquatic ecosystems. Such bioturbation can be caused by a variety of benthic macroinvertebrates or benthivorous fish that forage and burrow various bottom tubes, holes and pits. Thus, the processes involved may either be a result of direct interception by benthic animals, e.g., through bioresuspension of particles or through food ingestion and biodeposition, or of other indirect effects, e.g., changes in the physical properties of sediments or through the constructions mentioned above, along with corresponding changes in pond ecosystem functioning. The most distinct effect of benthivorous fish bioturbation activities is an increase in the turbidity of the water, which can lead to many subsequent knock-on effects, including inhibition of phytoplankton and submersed macrophyte growth with resulting alterations in physico-chemical water conditions. The importance of benthic macroinvertebrates and fish in bioturbation processes is also indicated by an increase in the numbers of resting cyanobacterial colonies recruited due to bioturbation of bottom sediments.     

Nutritional quality of amino acid in farmed,farm‐aggregated and wild Axillary seabream (Pagellus acarne) with implications to Human Health

This study evaluated the nutritional quality of farmed and wild axillary seabream (Pagellus acarne R., 1827) focusing on amino acid profiles, with regards to possible interactions with wild fish aggregating around the cage facility. Total amino acids (∑AA), essential amino acids (∑EAA), non‐essential amino acids (∑NEAA) and neutral amino acids (∑NAA) in farmed fish were lower than those in the wild individuals (p > .05). Amino acid pattern in cage‐aggregated fish showed a slight decline from the wild populations, but still higher than the farmed fish. Based on the amino acid scores (AAS), lysine and leucine could be underlined as the ‘first limiting amino acids’, but all other AASs were over ‘1’, in accordance with reference amino acid contents of FAO/WHO (>1.00), showing that farmed axillary seabream provides high nutritional quality and can be considered as a favourable protein source. The ratios of ∑EAA/∑AA (44%–46%) and ∑EAA/∑NEAA (79%–86%) exceeded the minimum recommendation of 40% and >60% by FAO/WHO for all three groups. It can be concluded that axillary seabream either farmed, farm‐aggregated or distant wild fish presented high‐quality protein generating a healthy source for human food.     

Effects of restricted feeding on growth of red sea bream and sedimentation of aquaculture wastes

For improving the economic and environmental sustainability of fish farming, it is necessary to optimize feeding regimes. From this viewpoint, we monitored the growth and mortality of red sea bream (Pagrus major), C and N fluxes and sediment chemistry at 2 commercial fish cages; cage 1 (conventional satiation feeding) and cage 2 (restricted feeding: same feeding frequency but 18% reduction in the feed amount) for 276 days. The similar specific growth rates (0.43% in cage 1 and 0.39% in cage 2) but different feed conversion efficiencies (0.54 in cage 1 and 0.62 in cage 2) and mortality (> 2-times higher in cage 1) between the 2 cages, indicate overfeeding in cage 1 culture. Elemental and stable isotopic analyses of sediment trap materials enabled the quantification of waste feed- and fecal matter-derived organic matter (OM) separately. The results shows that (1) aquaculture-derived OM comprised most of the fish-farm settling OM, excluding the period from January to April, when natural OM often accounted for a half of the bulk OM, (2) there was a difference in the seasonal trend between the fluxes of waste feed and fecal matter, and (3) there were no differences in the percentage compositions and fluxes of waste feed and fecal matter between the 2 cages. The isotopic analysis showed that the waste feed-derived OM in the sediment below cage 2 was 24% less than that below cage 1, suggesting effect of restricted feeding. Determining the relative amount of waste feed and fecal matter in settling and sedimentary OM is an effective method to evaluate the optimum feeding regime.     

沉积环境对鱼类网箱养殖的响应

网箱养殖是鱼类集约化养殖的主要方式,近年来得到大力发展,但是网箱养殖也带来诸多的环境问题。本文从沉积环境改变的角度阐述了网箱养殖对环境的影响,包括底层水环境要素、底质理化环境要素和底栖生物环境要素对网箱养殖的响应,并探讨了有机负荷的消减对策。网箱养殖区水环境中溶解氧(DO)通常下降,而化学耗氧量(COD)、氨氮(NH4-N)和无机磷(D IP)增多;底泥沉积物中N、P、硫化物、有机质等大量富集,其中富集现象最明显的是P、硫化物和NH4-N,其次是总氮(TN)和有机质;一般情况下,网箱养殖区底栖生物尤其是多毛类增加,而当污染严重时,会使底栖生物缺失。有机负荷的消减对策包括收集残饵粪便等沉积物、利用生物方法去除有机碎屑和加强养殖管理提高饲料利用率等。     

Water temperature regimes affect cataract development in smolting Atlantic salmon, Salmo salar L.

The effect of fluctuation in water temperature during the freshwater rearing stage on cataract development in Atlantic salmon was investigated. Presmolts were exposed to either constant low or high temperatures, or high temperature with cold-water fluctuations. Temperature fluctuations caused the fastest growth rate and most severe cataracts, whilst low temperature resulted in slow growth and minor cataracts. The fish were then individually marked and maintained together in a seawater net pen for 7 months. Cataract progressed in all groups, fish from the low temperature group showed the fastest subsequent growth, and developed cataracts to the same degree as fish from the other groups. There were no statistically significant differences in selenium-dependent glutathione peroxidase levels in pooled samples of aqueous humour, lens and plasma from fish with or without cataract, except from the last freshwater samples, where cataractous fish showed lower plasma activity. Plasma cortisol and glucose levels did not differ, nor did whole eye riboflavin levels. Higher concentrations of some free amino acids in whole eyes were found in fish with cataract. This study shows that fluctuation in water temperature may cause both increased growth rate and cataract development in Atlantic salmon and that cataract development initiated in the freshwater rearing phase continues after transfers to seawater.     

Ontogeny of swim bladder inflation and caudal fin aspect ratio with reference to vertical distribution in Pacific bluefin tuna Thunnus orientalis larvae

It is necessary to understand the processes involved in sinking death in Pacific bluefin tuna Thunnus orientalis aquaculture in order to develop methods to prevent or minimize this problem. We observed the nighttime vertical distribution of Pacific bluefin tuna in the water column on 2–9 DAH and the morphological characteristics of the larvae, in order to clarify the processes involved in sinking death. A cuboid tank (height 300 cm) was used to measure vertical distribution. The number of larvae was counted in each of 4 regions in the observation tank: upper layer (water depth 0–100 cm), middle layer (100–200 cm), lower layer (200–300 cm), and bottom area. The distribution of larvae in these regions at 4 days after hatching was polarized to the upper layer and bottom area. Individuals with inflated swim bladders were observed in the upper layer 3 days after hatching. No larvae with inflated swim bladders were observed in the bottom area on any day after hatching. Total body length and caudal fin aspect ratio of larvae with both inflated and un-inflated swim bladders were greater in the upper layer than those of larvae in the bottom area. Larvae with un-inflated swim bladders that failed to develop sufficiently for swimming sank to the tank bottom and died. Swim bladder development and caudal fin swimming ability are strongly related to sinking death.     

Assessment of the removal efficiency of fish farm effluents by grey mullets: a nutritional approach

A field study was carried out to assess the use of the bottom‐feeding grey mullet (Mugil cephalus) within benthic enclosures as a means to reduce the benthic impacts of a net cage fish farm in the Gulf of Aqaba, Red Sea. Five experimental 1‐m³ net‐cage enclosures were stocked with 12 grey mullets each (fish weights 50, 70 or 144 g). The enclosures had no bottom and the mullets had access to the enclosed organically enriched sediments and to particulate matter (PM) falling from the overlying cages. Sediment traps were used to quantify and qualify the PM falling from the fish farm to the sea floor. Simultaneously, a feeding trial was performed with mullets (50 and 70 g) in experimental tanks. In order to estimate the potential growth rate and to quantify energy and protein requirements, the fish were fed a formulated diet with known composition. After approximately 70 days at sea, mullets in the enclosures had used up all the available food in the sediment and gained up to 0.78 g day^?1 fish^?1. Applying the values for energy and protein requirements for maintenance and growth derived from the experimental trial, estimates indicated that the grey mullets effectively removed 4.2 g organic carbon, 0.70 g nitrogen and 7.5 mg phosphorus kg^?1 mullet m^?2 day^?1 from the organically enriched sediment. Thus deployment of grey mullets may be an efficient means to improve the quality of sediments below intensive net‐cage fish farms.     

Amino acids composition and protein quality evaluation of marine species and meals for feed formulations in cephalopods

The amino acid composition and protein levels of three species of cephalopods (Octopus vulgaris, Loligo gahi and Todarodes sagittatus), the natural diets of common octopus (O. vulgaris) and different kinds of meals were determined in order to optimise the content of these nutrients in artificial feeds. Arginine, leucine and lysine were the most abundant essential amino acids in cephalopods, while glutamate and aspartate represented the main non-essential amino acids. Arginine and leucine were the limiting amino acid in most samples, with maximum Chemical Score values for mussel (79–98 %), squid (84 %) and crustaceans (65–91 %); medium for fish (41–70 %); and minimum for meals (29–64 %). Mussel, squid, crustaceans and fish showed a high essential amino acid index according to Oser (OI: 88–99 %) suggesting a suitable amino acid balance. The protein from animal meals (fish and krill) covered all the essential amino acids except arginine and lysine in fish meal. The vegetable meal presented the worst amino acid balance (OI: 74–89 %) with several deficiencies in essential amino acids, including arginine, threonine, lysine and methionine. Supplementation with arginine or leucine and protein complementation of crustaceans and bivalves with fish or animal meal are proposed as alternatives for improving the performance of protein in feed for cephalopods.     

Phosphorus release rates from freshwater sediments affected by fish farming

The main wastes from fish production are fish faeces and uneaten feed, rich in nitrogen and phosphorus (P), which have the potential to alter the trophic state of the water body. It has been estimated that about 66% of P in fish feed accumulates on the bottom sediments. The P associated with these sediments can be released to the water column. The objectives of this work were to: (a) assess the release of phosphorus from sediments affected by intensive production of salmonids in two lakes in Patagonia, Argentina: Lago Moreno (PMOR ) and Alicura Reservoir (PALI ) ; (b) evaluate the efficiency of anionic exchange membranes (AEMs) for the determination of P release rates from sediments and compare this technique with the traditional chemical method; and (c) assess the usefulness of AEMs in estimating the labile fraction of phosphorus from sediments affected by fish farms. For all the conditions assayed, the release rates estimated with AEMs were higher than those estimated by syringe (n = 23, P= 0.001). The AEMs appear to have higher sensitivity than chemical methods, particularly at low concentrations. The AEMs are more reliable for the estimation of labile P, particularly in sediments low in labile P concentration. The difference between the release rates estimated by the AEMs and the syringe are indicative of the amount of labile P that will be available in the water over the short term. The release rates were higher under anaerobic conditions than under aerobic conditions for the two types of sediments affected by fish farms. The calcium and organic matter content of sediments, rather than the iron concentration, appears to control the availability of P.     

Benthic microbial indicators of fish farm impact in a coastal area of the Tyrrhenian Sea

We studied the impact of organic loads due to the biodeposition of a fish farm in a non-impacted coastal area of the Tyrrhenian Sea (Western Mediterranean). Sediment chemistry and benthic microbial community were investigated from July 1997 to February 1998 on monthly basis at two stations: one was located under the fish farm, while the second was about 1 km away, and served as a reference site. The presence of the cage induced rapid changes in the benthic conditions: the sediments were rapidly (after 6 weeks) reduced. A significant accumulation of biopolymeric carbon was observed beneath the cage both 2 weeks after the initial cage deployment, on non-impacted sediments, and 5–7 months after, and appeared to be related to the fish farm production cycle. The density of microbial communities beneath the fish farm increased only during the first month of farming activity (July) and partially 7 months after cage disposal (i.e. in January), when there was a significant sediment organic enrichment. Additional evidence of rapid impact of the fish farm on the benthic bacterial communities is provided by the increase in the numbers of autofluorescent microbial cells. The photosynthetic eukaryotic cells displayed a highly reduced contribution to total autofluorescent microbial density, indicating that their decrease is related with biopolymeric carbon accumulation, and probably was due also to “shadow effect” induced by suspended material, coming from the fish farm, on the environment below. We propose here, to apply the ratio of culturable heterotrophic bacteria to microbial direct counts (CFU/MDC) to detect fish farm impact. In cage sediments, organic enrichment and the consequent modification of the characteristics of the benthic environment, determined an increase in aerobic heterotrophic bacteria and vibrio density indicating that they are efficient colonizers of organic-rich sediments. Densities of Escherichia coli and Enterococci were not significantly higher than in the reference site, and are likely of terrestrial origin. Thus they cannot be used as specific indicators of fish farm impact.     

Sedimentation and Resuspension in Earthen Fish Ponds

Resuspension of particles from pond sediment into the water column may be an important nutrient transfer mechanism in aquaculture ponds. However, the magnitude of sediment re-suspension cannot be determined directly because sediment traps collect particles settling from the water column as well as those re-suspended from the pond bottom. We developed a dilution analysis method to differentiate the magnitude of the two particle source fluxes based upon the concentration of soil-derived elements (Si, Al, and Fe) and water-derived elements (C, N) in material collected by sediment traps placed in earthen ponds. Estimated organic C sedimentation from feed residues and algae was compared with trapped organic C as an independent and approximate measure of resuspension. Resuspension fluxes based independently on analyses of three soil-derived elements and on the estimation of expected C sedimentation were similar and accounted for 60–90% of the total solids flux (121–2,676 g/m² per d) in most ponds sampled. The proportion of total flux that was derived from resuspension in ponds stocked with common carp Cyprinus carpio and tilapia Oreochromis spp . was modeled as a hyperbolic function of fish size and density, with a threshold fish size of 200–300 g. Resuspension flux was conservatively estimated to be equivalent to the daily suspension of a few mm of the pond bottom. These results indicate that sediment resuspension is a major process in carp and tilapia ponds, suggesting that the exchange of nutrients between the sediment and overlying water is intensive.