The e¡ects of aquarium background colour and feed colour on survival, growth rates and feed utilization ef-¢ciency of thinlip mullet (Liza ramada) larvae (0.035 g) were investigated in two experiments. In the aquarium background colour trial, 50 larvae were stocked in duplicates in 120 L glass aquaria ¢lled with dechlorinated tap water. The outside walls and bottoms of each pair of the aquaria were covered with coloured paper sheets to achieve one of six colours (white, black, red, green, yellow and blue), while noncoloured aquaria served as a control. The ¢sh were fed an experimental diet (35% crude protein) at a daily rate of 5% of their body weight (BW), twice a day for 8 weeks. The best growth rates, feed e⁄ciency and survival were achieved in larvae reared in light-coloured aquaria (white, noncoloured and yellow). Fish performance was signi¢cantly retarded in larvae reared in dark-coloured aquaria (red, green, black and blue). Bodycomposition was not significantly a¡ected by aquarium colour. In a feed colour trial, duplicate groups of larvae (0.035 g) were stocked at 50 ¢sh per 120 L aquarium and fed a test diet (35% crude protein) with six di¡erent colours [dark blue, red, yellow, light brown (control), light green and dark brown] at a daily rate of 5% BW, twice a day for 8 weeks. The best performance and survival were achieved in ¢sh fed on dark-coloured diets (red, dark blue and dark brown). Light-coloured diets (yellow, light green and light brown) resulted in inferior performance. Body composition was not signi¢cantly a¡ected by feed colour. These results suggest that light-coloured tanks should be used for rearing thinlip mullet, L. ramada larvae, while dark-coloured diets are more preferable to light-coloured diets.

No abstract

The effects of varying water depths and temperature on the growth, feed utilization, mortality rates and body composition of Nile tilapia, Oreochromis niloticus (L.), were evaluated. Triplicate groups of 20 fish (mixed‐sex) m‐3 were stocked into 200‐m2 freshwater earthen ponds maintaining four water depths: 50, 100, 200 and 300 cm. The fish were fed on commercial fish pellets (23% protein), twice a day for 10 months (May 1991‐February 1992). Water temperatures ranged from 5 oC to 33 oC. Growth performance and survival were significantly affected by pond depth and water temperature. Fish weight gain was lowest (250 g per fish), feed conversion poorest (3.15), and mortality highest (41.5%) at 50 cm depth, whereas 100‐200 cm depth produced the best growth rates at warm water temperatures (> 21 oC). At 100‐200 cm depth, weight gain was significantly (P<0.001) increased to 348‐362 g per fish, feed conversion improved to 2.53‐2.59 (P<0.01) and mortality reduced to 21‐27% (P<0.001). Fish growth was significantly reduced (P<0.001) below 21 oC. Below 10 oC, fish stopped feeding and developed severe stress, fungal infection and high mortality. However, mortality rate was significantly reduced at 300 cm depth. Body lipid and protein were sharply decreased (P<0.001) with decreasing water temperature and pond depth, whereas body ash showed irregular patterns.

Abstract.— The effects of thermal and thermo/haline shocks on the tilapias Oreochromis mossambicus and O. aureus × O. niloricus hybrids were investigated. Fingerlings were transferred abruptly from 25 C fresh water to fresh water or salt water (26 ppt) maintaining temperatures of 15, 20, 30 and 35 C. In fresh water, fish survival was not affected by temperature shock, but they suffered from a chill coma and developed fungal infection at 15 C. In salt water, thermo‐haline shock did not affect the survival of O. mossambicus, while the survival rates of tilapia hybrids were 6.7, 100, 100, 70 and 59.7% at 15, 20, 25, 30 and 35 C, respectively. Plasma osmotic concentrations of O. mossambicus transferred to 15 and 35 C salt water were quickly and sharply increased, but gradually decreased to lower levels. Osmotic concentrations of tilapia hybrids were also increased, but never returned to their initial (lower) levels over one week. This study revealed that these fishes are more tolerant to high rather than low temperature shocks and O. mossambicus are more resistant to thermo‐haline shocks rather than tilapia hybrids. It also indicated that thermo‐haline shocks should be minimized during fish transportation and acclimation.

Coastal aquaculture is faced with extreme variation in water quality. The Deeba Triangle on Lake Manzala is the largest marine coastal aquaculture-producing area on the Egyptian Mediterranean. Samples from 16 ponds were taken during four seasons (2014-2015), to investigate the variation of 12 water quality parameters at that region. We tested the hypothesis that there is no spatial or temporal variation in water quality of the fish ponds. Fish ponds were statistically clustered into three groups (p = 0.0005) coincident with their geographical location. Hypersaline and transparent waters characterized the western ponds; higher dissolved oxygen and higher nutrients characterized the central region. These spatial differences were principally due to variations in salinity and nutrients of the water sources used for irrigation of the ponds and to differences in the aeration management styles. Strong seasonality was seen in water temperature (following air temperature), nutrients, and turbidity (following the seasonal cycles of various water sources from the Lake Manzala and the seasonality of the petrochemical plants effluents close to these ponds). We conclude that municipal effluents significantly affected, spatially and temporally, the quality of the irrigation water used for coastal aquaculture purposes, which consequently might affect fish yield.