Growth of Hybrids of Sarotherodon melanotheron (Rüppell, 1852) and Oreochromis niloticus (Linnaeus, 1758) in the Area of Lake Ahémé and Its Channels ^†

Abstract

The Ahémé Lake and its channels make up the saline area in Benin and do not facilitate the breeding of freshwater fish. The cross between the parents of Oreochromis niloticus and Sarotherodon melanatheron allowed us to obtain hybrids that grow in brackish water. It is a totally randomized device with four treatments and two repetitions. The larvae were brought back and fed to satiety for 6 weeks. The growth rates of the OS hybrids were 0.38 g/day, while those of the SO hybrids were 0.33 g/day. OS hybrids are an excellent candidate for fish farming in a brackish environment.

1. Introduction

Fishing is a socio-economic activity that plays an important role in human nutrition [1]. Fish, the main source of protein for populations in southern Benin, is provided by water bodies [2]. However, ever-increasing demographic pressure, coupled with the erosion of banks and poor fishing practices have led to a degradation of the aquatic ecosystem and a drop in fish production [3]. Fish farming is, therefore, an essential alternative to meet the dietary needs of populations in fish protein. However, in the area of Lake Ahémé and its channels, the soils are salty for a good period of the year because of the connection of the environment with the sea [4]. However, the fast-growing fish species that are currently farmed in Benin are freshwater [5], which hinders the development of fish farming in the study area. Faced with this situation, the solution found is to cross the parents of a fast-growing freshwater species (Oreochromis niloticus) with the parents of a species supporting brackish water and medium growth (Sarotherodon melanotheron), whose goal is to obtain hybrids with rapid growth and supporting brackish water. However, what are the standards of this crossing? How should the hybrid larvae obtained be followed? This is the purpose of this article, which aims to improve fish production with hybrids resulting from the crossing of S. melanotheron and O. niloticus in the Lake Ahémé area and its channels. Specifically, it involves evaluating the optimal conditions for obtaining hybrids, to analyze the growth parameters of the hybrid larvae obtained and to identify the population of hybrids with the best zootechnical performance for a fish farm.

2. Material and Method

2.1. Study Area

The study area includes Lake Ahémé, the Ahô channel, the coastal lagoon of Grand-Popo, the coastal lagoon of Ouidah and the Tihimey channel. Lake Ahémé receives the waters of the Couffo River and flows into the Ahô channel and the Tihimey channel. The Ahô channel flows into the coastal lagoons of Grand-Popo and Ouidah [6]. The coastal lagoon of Grand-Popo receives the waters of the Mono River and flows into the sea through the mouth “Bocca Del Rio”. The coastal lagoon of Ouidah, for its part, takes its source from the lagoon of Grand-Popo and the Ahô channel. The presence of the mouth makes the study area a very diversified lagoon estuary environment. Rainfall varies from 800 to 1200 mm per year, characterized by the alternation of two rainy seasons (April–July and October–November) and two dry seasons (December–March and August–September).

2.2. Biological Material

Table 1. Broodstock used and their origins.

Parents	Origins	Sex	Numbers	Average Weight (g)
Oreochromis niloticus	Fish pond at the “La main de Dieu” farm in Comê	Male	10	110
		Female	21	150
Sarotherodon melanotheron	Ahémé Lake	Male	50	53.2
		Female	22	45

summarizes the origins and number of broodstock used for the trial. The S. melanotheron come from Lake Ahémé, while those of O. niloticus are purchased from a fish farm located in the study area. They are divided by sex and quarantined for 15 days in small tanks measuring 1 m × 1 m × 0.8 m and fed with 3 mm granulated feed from the “le gouéssant” brand.

2.3. Experimental Apparatus

Two basins 6 m long, 2 m wide with a depth of 1.5 m each were used. Four fish tanks of 1.5 m width with a depth of 1.5 m each were installed in each basin. These tanks were used to serve as protection for the various crossings. It is a totally randomized device with 4 treatments and 2 repetitions [7]. The fish were fed a diet composed of 9.00% fat, 32% crude protein, 2.94% crude ash, 0.88% calcium, 0.91% total phosphate and 0.15% sodium. The ration was 2.5%, served morning and evening. After obtaining the larvae, they were monitored with the same device at a rate of 120 larvae per tank. These larvae were then fed to satiety twice a day over a period of 6 weeks. The Kruskhal–Wallis test was used to verify the degree of significance of the variations. The test is a trial conducted in 2020.

3. Results

3.1. Obtaining Hybrid Larvae

The first larvae obtained are those of the control crosses; O. niloticus after 7 days and S. melanotheron, 15 days after crossing. As for the hybrid larvae, they are obtained 45 days after crossing.

3.2. Growth Parameters

Table 2. Results from analysis of average fry growth.

Variables	Minimum	Maximum	Moy	StDev	Variance	CoefVar
OO	9.50	29.00	22.83	7.29	53.17	31.93
SS	10.00	20.25	16.49	3.63	13.18	22.01
OS	9.90	24.75	18.54	5.29	27.93	28.50
SO	9.85	22.50	17.58	4.45	19.81	25.32

OO = larvae from the control cross O. niloticus; SS = larvae from the control cross S. melanotheron; OS = hybrids from the OS test cross; SO = hybrids from the SO test cross; CoefVar = Coefficient of variation Avg. = Average; StDev = Standard Deviation.

presents the evolution curves of the average growth of the larvae harvested after the various crosses carried out. We noticed:

• OO the fry from the control cross of the parents of O. niloticus.
• SS the fry from the control cross of the parents of S. melanotheron.
• OS the fry from the test cross “male S. melanotheron crossed by female O. niloticus”.
• SO the fry from the test cross “male O. niloticus crossed by female S. melanotheron”.

This table shows an almost similar upward evolution of the growth curves. Nevertheless, we found that the fry growth curve of O. niloticus (OO) is well above the other three. It is followed by that of the hybrids from the test cross “male S. melanotheron crossed by female O. niloticus” (OS) then by that of the hybrids resulting from the test cross “male O. niloticus crossed by female S. melanotheron” (SO), and finally, that of the fry of S. melanotheron (SS). The results given by the statistical analysis also showed that the average growth of the OO fry (23.83 g) is higher than that of the other fry. That of OS fry (18.54 g) comes in second position followed by that of SO fry (17.58 g), which is ahead of SS fry (16.49 g).

4. Discussion

Regarding reproduction, crosses took a long time to produce larvae (45 days). This situation is due to S. melanotheron, which are found in a controlled environment. This time is greater than that observed by Chowdhury [8] in pure breeding ponds for the species. The survival rate of OS hybrid fry is higher than that of SO hybrid fry, which are 88.83% and 85%, respectively. These survival rates show us that the OS hybrid fry would have inherited a better survival performance from their parents, the females of O. niloticus and the males of S. melanotheron. In other hybrid growth monitoring studies, the survival rate of O. niloticus fry is relatively lower than that of S. melanotheron fry and SO and OS hybrids [9]. This is because the monitoring was carried out in the water of the lagoon in Côte d’Ivoire at a salinity higher than that of fresh water (0 to 5 g/L). In this case, we can say that the hybrids inherited the best adaptability from their S. melanotheron parents, which resist salinities ranging from 5 to 110 g/L. The calculated growth parameters show that during the 42 days of rearing, the fry of O. niloticus had a better average daily gain (0.46 g/d), the OS hybrids followed with an average daily gain of 0, 38 g/d, then the SO hybrids (0.33 g/d), and finally, the fry of S. melanotheron, with a daily weight gain of 0.29 g/d. Previous studies show strong growth of O. niloticus in ponds with an average daily gain (ADG) of 0.70 g/d [10]. The growth of the hybrids was, on the other hand, stronger than that of S. melanotheron. It was intermediate between those of O. niloticus and S. melanotheron, which confirms the previous work of Amon [11]. This last result is also in line with that of Toguyéni [12], on hybrids resulting from artificial insemination between O. niloticus and S. melanotheron.

5. Conclusions

The growth of Sarotherodon melanotheron (Rüppell, 1852) and Oreochromis niloticus (Linnaeus, 1758) hybrids in the Lake Ahémé area and its channels shows that these species manage to reproduce to provide hybrids that constitute a solution to the development of aquaculture in salty areas in Benin. In terms of survival in a lagoon environment, we can, therefore, conclude that the hybrids resulting from the crosses of O. niloticus and S. melanotheron will have a better survival performance compared to their O. niloticus parents. We can, therefore, affirm that the male hybrids result from the cross ♀ O. niloticus × ♂ S.