African Journals Online
Tropical Freshwater Biology

VOL. 8 1999
ABSTRACTS

Cumulative Impact of Effluents on Plankton Dynamics in Awba Reservoir, Ibadan

G.A. Akin-Oriola ¹ and C.Y. Jeje ²

¹Fisheries and Zoology Department, Lagos State University, Nigeria

²Zoology Department, University of Ibadan, Nigeria

Abstract

The assessment of changes in the biological community of water is a very sensitive measure of its quality. The plankton community structure of Awba reservoir in the University of Ibadan, Nigeria was monitored between April and October 1989 to determine the impact of natural eutrophication and effluent discharge on its dynamics. Generally, the dissolved oxygen content, pH, conductivity and ammonia-nitrogen values indicated a deterioration in water quality at stations receiving organic or chemical effluents. The plankton structure was characterized by a blue-green algae - Protozoa dominated community. The Simpson’s diversity index at all stations was less than one implying a heterogeneous community where a few species dominated.

KEY WORDS: effluents - water quality - Simpson’s diversity index - plankton community structure

Acute Toxicity Of Refined Oil On The Catfish, Clarias gariepinus (Teugels, 1984) (Pisces: Clariidae)

O. Kori-Siakpere & E.E. Akiri,

Department of Zoology, Delta State University, P.M.B. 1, Abraka, Nigeria.

Abstract

Laboratory static bioassays were conducted to determine the 24-, 48-, and 96 -hour LC₅₀ and the lethal levels of concentrations of oil-in-water dispersions (OWD) of used and fresh fuel oil for embryo, fry and fingerlings of the catfish Clarias gariepinus(Teugels, 1984). The most sensitive was the embryonic stage while the fingerlings were most resilient. The LC₅₀ values obtained for treatment with fresh fuel oil were as follows: Embryos (24- and 48 -hour LC₅₀) 0.034 ml/l and 0.042 ml/l respectively. For the fry (24-, 48-, 72- and 96-hour) the LC₅₀ values were 1.22ml/l, 0.85ml/l, 0.83ml/l and 0.70ml/l respectively. The fingerlings had 48-, 72 and 96-hour LC₅₀ values of 5.00 ml/l, 2.30 ml/l and l.78ml/l respectively. The LC₅₀ values for treatment with used fuel oil were as follows: Embryos (24 - and 48 -hour LC₅₀) 0.032 ml/l and 0.04 ml/l respectively. For the fry (24-, 48-, 72-and 96-hour LC₅₀) values were 1.59 ml/l, 1.14 ml/l, and 1.12 ml/1 while the fingerlings had 0.82 ml/l, 1 .37 ml/l and 1.02 ml/l as their 48-, 72- and 96-hour LC₅₀ values respectively. Loss of skin pigmentation was observed in fish exposed to fresh fuel oil and darker pigmentation in fish exposed to used oil. Activity generally decreased with increased concentration of toxicant and longer duration of exposure. A similar trend was observed for hatchability of the embryos. Increased mouth and opercular breathing were also observed.

KEY WORDS: Petroleum-Refined Oil-Toxicity-Behaviour-Clarias gariepinus, Nigeria.

Correlation of Some Environmental Variables with Adaptive Net–Spinning Strategies in Stream Larval Hydropsychids (Trichoptera) in Garhwal Himalaya

(Short Communication)

Neeraj Kumar and Anoop K. Dobriyal

Department of Zoology, HNB Garhwal University Campus, Pauri Garhwal – 246 001, UP., India.

Introduction

The Hydropsychidae (Trichoptera) being the master spinners of freshwater rapids spin the net s of various sizes required during different seasons, and for different instars. Also they adopt strategies for coexistence between similar and different species by selecting various mesh sizes, current regimes, and habitat modes. The paper highlights the results of the study on the various net spinning strategies and associated environmental variables. In two larval hydropsychids from a small stream ‘Malethagaad in the Garhwal, Central Himalaya (India). Among net – spinning Hydropsychidae, the effect of certain seasonal environmental variables was studied and the most influencing ones recognised were water temperature changes, current speed, and increase in resource particulate concentration downstream.

It was observed that in response to increase in all the above parameters (except temperature) net – spinning activity increases, reducing the size of mesh and thus successfully enabling the animal to adjust to the drag of the water current and particle filtration requirements with relation to the body size and microclimate of the dwelling mode.

Certain anomalies were observed in hydropsychid capture nets from lotic sidewater pools and an increase in temperature probably also triggered an increase in net – spinning activity during summer, but the mesh shapes and sizes vary. Also probably the behavioural and morphological differences of various instars considered, facilitated in adaptive strategies for coexistence between similar and different species.

Summary

1.   The Hydropsyche k₁ and Hydropsyche k₂ divide up net spinning sites by partial differences in water velocity preferences, use of different dwelling crevices and modes of habitat.

2.   The catch net mesh was found to be related to current speeds, resource particle requirements and the morphological stages of various instars and the combination of these variables may be taken as deciding factor as to how the mesh size is determined in a particular species to facilitate coexistence among different and similar instars of the same and different putative species.

3.   Also the correlation of body size and net dimensions along with the distribution on the stream, with the increased resource particle concentration downstream and larger instars downstream point towards a natural distributional strategy enabling a successful species propagation for instars associated.

Invertebrate Fauna Associated with Water Hyacinth (Eichhornia crassipes) in Benin River, Southern Nigeria.

J. K. Ekelemu

Department of Animal Science and Fisheries, Delta State University, Asaba Campus, Asaba Nigeria.

A. B. M. Egborge

Zoology Department, University of Benin, Benin City, Nigeria and

P. A. Ekokotu

Department of Animal Science and Fisheries, Delta State University, Asaba Campus, Asaba Nigeria.

Abstract

The invertebrate fauna associated with water hyacinth (Eichhornia crassipes) in Benin River was studied between February and August, 1990. Water hyacinth along with water samples was collected for analysis. The range of water temperature was 26.0–32.2^oC, dissolved oxygen (D.O) was 1.60–14.98 mgl^-1 and salinity was 0.42-6.84^o/_oo. Twenty-two (22) species of organisms attached to the roots of the plant were recognized. Gastropods, which made up 41.24% of the total faunal population, were the most abundant, while the annelids were the least, numerically making up only 0.08% of the faunal population. Colonisation of the roots of water hyacinth, was multiple factor dependent.

KEY WORDS: nutrients - macrophytes - estuary - brackish water - freshwater - fauna.

Helminth Parasites of Some Tropical Freshwater Fish From Osse River in Benin, Southern Nigeria

C. E. Okaka

Zoology Department, University of Benin, Benin City, Nigeria. and

J. E. Akhigbe

Veterinary Division, Ministry of Agriculture and Natural Resources, Benin City, Nigeria.

Abstract

Investigations into helminth parasites of freshwater fish from Osse River, Benin, revealed an overall 17.1% infection rate. Of the twelve species of fish studied, Barbus sp. had the heaviest infection rate (2.2%) while Xenomystus nigrihad the least (1.0%). Parasites recovered were the tematodes Clinostomum tilapiae, Clinostomum sp, Allocreadium sppand Diplostomum tragenna; the cestodes Polyonchobothrium sp. and Proteocephalus sp; the acanthocephalan Acanthogyrus (Acanthosentis) tilapiae; and the nematodes Camallanus sp; Procamallnus laeviconchus; Spinitectus sp; Spirocamallanus sp; Serradactnitis sp; and Spironoura sp. Nematode infection had the highest prevalence of 7.7% while trematodes recorded the least of (1.9%). A seasonal pattern of infection was demonstrated with a high infection rate in the rainy season months of June to November and a low infection rate in the dry season months of December to May.

KEY WORDS: helminth parasites – prevalence - freshwater fish - seasonal effects.

Temperature, Latency and Incubation Time of Clarias gariepinus, Heterobranchus longifilis and their Hybrids

O. J. Abolagba

Fisheries Department, Faculty of Agriculture University of Benin, Benin City, Nigeria

Abstract

Latency and incubation periods of Clarias gariepinus, Heterobranchus longifilis and the incubation period of C. gariepinuseggs fertilized with sperm of H. longifiliswere studied. There was a negative correlation between the water temperature, latency and incubation periods for the two species and their hybrids.

The latency time for C. gariepinus changed (dropped) at the rate of 1.30 hours for every 1°C raise/increase in water temperature, and for H. longifilis the rate was 1.50 hours for every 1°C. However, the incubation periods showed the rate of change for C. gariepinus to be 3.33 hours; and H. longifilis4.02 hours for every 1°C increase in water temperature.

For the hybrid, the incubation period dropped at the rate of 3.57 hours for every 1°C increases in water temperature.

KEY WORDS: Latency – incubation - Clarias gariepinu - Heterobranchus longifilis – Hybrid - Brood fish.

Digestive Enzymes in the Alimentary Canal of Clarias anguillaris (Pisces: Clariidae)

O. Kori-Siakpere

Department of Zoology, Delta State University, P.M.B 1., Abraka, Nigeria.

Abstract

Three groups of digestive enzymes were observed in the alimentary canals of the fingerlings and adults of Clarias anguillaris. The enzymes were carbohydrases including amylase, sucrase, lactase and maltase, proteases including peptase, tryptase and peptidase, and lipase. The activities of the protease were found to be higher in the fingerlings than in the adults while carbohydrases’ activities were higher in the adults than fingerlings. Amylase was most widely distributed, found in both fingerlings and adults and in every region studied; it was followed by lactase. Of the proteases, peptase was found to have the widest distribution. Lipase activity was found in the alimentary canal of the adults.

KEY WORDS: digestive enzymes – carbohydrases – proteases – lipases - Clarias anguillaris